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sqlite/src/wal.c
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dan 05573e41a8 Lock the wal file for all snapshot transactions, even if they would not 
otherwise require this, preventing checkpointers and writers from wrapping the
wal file. This means that if one connection has an open snapshot transaction
it is guaranteed that a second connection can open a transaction on the same
snapshot.

FossilOrigin-Name: b81a31495bd27c1d96f7df653da3502054240cb5acf66b860da7f0f9b422a524
2017-11-28 13:39:41 +00:00

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/*
** 2010 February 1
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file contains the implementation of a write-ahead log (WAL) used in
** "journal_mode=WAL" mode.
**
** WRITE-AHEAD LOG (WAL) FILE FORMAT
**
** A WAL file consists of a header followed by zero or more "frames".
** Each frame records the revised content of a single page from the
** database file. All changes to the database are recorded by writing
** frames into the WAL. Transactions commit when a frame is written that
** contains a commit marker. A single WAL can and usually does record
** multiple transactions. Periodically, the content of the WAL is
** transferred back into the database file in an operation called a
** "checkpoint".
**
** A single WAL file can be used multiple times. In other words, the
** WAL can fill up with frames and then be checkpointed and then new
** frames can overwrite the old ones. A WAL always grows from beginning
** toward the end. Checksums and counters attached to each frame are
** used to determine which frames within the WAL are valid and which
** are leftovers from prior checkpoints.
**
** The WAL header is 32 bytes in size and consists of the following eight
** big-endian 32-bit unsigned integer values:
**
** 0: Magic number. 0x377f0682 or 0x377f0683
** 4: File format version. Currently 3007000
** 8: Database page size. Example: 1024
** 12: Checkpoint sequence number
** 16: Salt-1, random integer incremented with each checkpoint
** 20: Salt-2, a different random integer changing with each ckpt
** 24: Checksum-1 (first part of checksum for first 24 bytes of header).
** 28: Checksum-2 (second part of checksum for first 24 bytes of header).
**
** Immediately following the wal-header are zero or more frames. Each
** frame consists of a 24-byte frame-header followed by a <page-size> bytes
** of page data. The frame-header is six big-endian 32-bit unsigned
** integer values, as follows:
**
** 0: Page number.
** 4: For commit records, the size of the database image in pages
** after the commit. For all other records, zero.
** 8: Salt-1 (copied from the header)
** 12: Salt-2 (copied from the header)
** 16: Checksum-1.
** 20: Checksum-2.
**
** A frame is considered valid if and only if the following conditions are
** true:
**
** (1) The salt-1 and salt-2 values in the frame-header match
** salt values in the wal-header
**
** (2) The checksum values in the final 8 bytes of the frame-header
** exactly match the checksum computed consecutively on the
** WAL header and the first 8 bytes and the content of all frames
** up to and including the current frame.
**
** The checksum is computed using 32-bit big-endian integers if the
** magic number in the first 4 bytes of the WAL is 0x377f0683 and it
** is computed using little-endian if the magic number is 0x377f0682.
** The checksum values are always stored in the frame header in a
** big-endian format regardless of which byte order is used to compute
** the checksum. The checksum is computed by interpreting the input as
** an even number of unsigned 32-bit integers: x[0] through x[N]. The
** algorithm used for the checksum is as follows:
**
** for i from 0 to n-1 step 2:
** s0 += x[i] + s1;
** s1 += x[i+1] + s0;
** endfor
**
** Note that s0 and s1 are both weighted checksums using fibonacci weights
** in reverse order (the largest fibonacci weight occurs on the first element
** of the sequence being summed.) The s1 value spans all 32-bit
** terms of the sequence whereas s0 omits the final term.
**
** On a checkpoint, the WAL is first VFS.xSync-ed, then valid content of the
** WAL is transferred into the database, then the database is VFS.xSync-ed.
** The VFS.xSync operations serve as write barriers - all writes launched
** before the xSync must complete before any write that launches after the
** xSync begins.
**
** After each checkpoint, the salt-1 value is incremented and the salt-2
** value is randomized. This prevents old and new frames in the WAL from
** being considered valid at the same time and being checkpointing together
** following a crash.
**
** READER ALGORITHM
**
** To read a page from the database (call it page number P), a reader
** first checks the WAL to see if it contains page P. If so, then the
** last valid instance of page P that is a followed by a commit frame
** or is a commit frame itself becomes the value read. If the WAL
** contains no copies of page P that are valid and which are a commit
** frame or are followed by a commit frame, then page P is read from
** the database file.
**
** To start a read transaction, the reader records the index of the last
** valid frame in the WAL. The reader uses this recorded "mxFrame" value
** for all subsequent read operations. New transactions can be appended
** to the WAL, but as long as the reader uses its original mxFrame value
** and ignores the newly appended content, it will see a consistent snapshot
** of the database from a single point in time. This technique allows
** multiple concurrent readers to view different versions of the database
** content simultaneously.
**
** The reader algorithm in the previous paragraphs works correctly, but
** because frames for page P can appear anywhere within the WAL, the
** reader has to scan the entire WAL looking for page P frames. If the
** WAL is large (multiple megabytes is typical) that scan can be slow,
** and read performance suffers. To overcome this problem, a separate
** data structure called the wal-index is maintained to expedite the
** search for frames of a particular page.
**
** WAL-INDEX FORMAT
**
** Conceptually, the wal-index is shared memory, though VFS implementations
** might choose to implement the wal-index using a mmapped file. Because
** the wal-index is shared memory, SQLite does not support journal_mode=WAL
** on a network filesystem. All users of the database must be able to
** share memory.
**
** In the default unix and windows implementation, the wal-index is a mmapped
** file whose name is the database name with a "-shm" suffix added. For that
** reason, the wal-index is sometimes called the "shm" file.
**
** The wal-index is transient. After a crash, the wal-index can (and should
** be) reconstructed from the original WAL file. In fact, the VFS is required
** to either truncate or zero the header of the wal-index when the last
** connection to it closes. Because the wal-index is transient, it can
** use an architecture-specific format; it does not have to be cross-platform.
** Hence, unlike the database and WAL file formats which store all values
** as big endian, the wal-index can store multi-byte values in the native
** byte order of the host computer.
**
** The purpose of the wal-index is to answer this question quickly: Given
** a page number P and a maximum frame index M, return the index of the
** last frame in the wal before frame M for page P in the WAL, or return
** NULL if there are no frames for page P in the WAL prior to M.
**
** The wal-index consists of a header region, followed by an one or
** more index blocks.
**
** The wal-index header contains the total number of frames within the WAL
** in the mxFrame field.
**
** Each index block except for the first contains information on
** HASHTABLE_NPAGE frames. The first index block contains information on
** HASHTABLE_NPAGE_ONE frames. The values of HASHTABLE_NPAGE_ONE and
** HASHTABLE_NPAGE are selected so that together the wal-index header and
** first index block are the same size as all other index blocks in the
** wal-index.
**
** Each index block contains two sections, a page-mapping that contains the
** database page number associated with each wal frame, and a hash-table
** that allows readers to query an index block for a specific page number.
** The page-mapping is an array of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE
** for the first index block) 32-bit page numbers. The first entry in the
** first index-block contains the database page number corresponding to the
** first frame in the WAL file. The first entry in the second index block
** in the WAL file corresponds to the (HASHTABLE_NPAGE_ONE+1)th frame in
** the log, and so on.
**
** The last index block in a wal-index usually contains less than the full
** complement of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE) page-numbers,
** depending on the contents of the WAL file. This does not change the
** allocated size of the page-mapping array - the page-mapping array merely
** contains unused entries.
**
** Even without using the hash table, the last frame for page P
** can be found by scanning the page-mapping sections of each index block
** starting with the last index block and moving toward the first, and
** within each index block, starting at the end and moving toward the
** beginning. The first entry that equals P corresponds to the frame
** holding the content for that page.
**
** The hash table consists of HASHTABLE_NSLOT 16-bit unsigned integers.
** HASHTABLE_NSLOT = 2*HASHTABLE_NPAGE, and there is one entry in the
** hash table for each page number in the mapping section, so the hash
** table is never more than half full. The expected number of collisions
** prior to finding a match is 1. Each entry of the hash table is an
** 1-based index of an entry in the mapping section of the same
** index block. Let K be the 1-based index of the largest entry in
** the mapping section. (For index blocks other than the last, K will
** always be exactly HASHTABLE_NPAGE (4096) and for the last index block
** K will be (mxFrame%HASHTABLE_NPAGE).) Unused slots of the hash table
** contain a value of 0.
**
** To look for page P in the hash table, first compute a hash iKey on
** P as follows:
**
** iKey = (P * 383) % HASHTABLE_NSLOT
**
** Then start scanning entries of the hash table, starting with iKey
** (wrapping around to the beginning when the end of the hash table is
** reached) until an unused hash slot is found. Let the first unused slot
** be at index iUnused. (iUnused might be less than iKey if there was
** wrap-around.) Because the hash table is never more than half full,
** the search is guaranteed to eventually hit an unused entry. Let
** iMax be the value between iKey and iUnused, closest to iUnused,
** where aHash[iMax]==P. If there is no iMax entry (if there exists
** no hash slot such that aHash[i]==p) then page P is not in the
** current index block. Otherwise the iMax-th mapping entry of the
** current index block corresponds to the last entry that references
** page P.
**
** A hash search begins with the last index block and moves toward the
** first index block, looking for entries corresponding to page P. On
** average, only two or three slots in each index block need to be
** examined in order to either find the last entry for page P, or to
** establish that no such entry exists in the block. Each index block
** holds over 4000 entries. So two or three index blocks are sufficient
** to cover a typical 10 megabyte WAL file, assuming 1K pages. 8 or 10
** comparisons (on average) suffice to either locate a frame in the
** WAL or to establish that the frame does not exist in the WAL. This
** is much faster than scanning the entire 10MB WAL.
**
** Note that entries are added in order of increasing K. Hence, one
** reader might be using some value K0 and a second reader that started
** at a later time (after additional transactions were added to the WAL
** and to the wal-index) might be using a different value K1, where K1>K0.
** Both readers can use the same hash table and mapping section to get
** the correct result. There may be entries in the hash table with
** K>K0 but to the first reader, those entries will appear to be unused
** slots in the hash table and so the first reader will get an answer as
** if no values greater than K0 had ever been inserted into the hash table
** in the first place - which is what reader one wants. Meanwhile, the
** second reader using K1 will see additional values that were inserted
** later, which is exactly what reader two wants.
**
** When a rollback occurs, the value of K is decreased. Hash table entries
** that correspond to frames greater than the new K value are removed
** from the hash table at this point.
*/
#ifndef SQLITE_OMIT_WAL
#include "wal.h"
/*
** Trace output macros
*/
#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
int sqlite3WalTrace = 0;
# define WALTRACE(X) if(sqlite3WalTrace) sqlite3DebugPrintf X
#else
# define WALTRACE(X)
#endif
/*
** The maximum (and only) versions of the wal and wal-index formats
** that may be interpreted by this version of SQLite.
**
** If a client begins recovering a WAL file and finds that (a) the checksum
** values in the wal-header are correct and (b) the version field is not
** WAL_MAX_VERSION, recovery fails and SQLite returns SQLITE_CANTOPEN.
**
** Similarly, if a client successfully reads a wal-index header (i.e. the
** checksum test is successful) and finds that the version field is not
** WALINDEX_MAX_VERSION, then no read-transaction is opened and SQLite
** returns SQLITE_CANTOPEN.
*/
#define WAL_MAX_VERSION 3007000
#define WALINDEX_MAX_VERSION 3007000
/*
** Index numbers for various locking bytes. WAL_NREADER is the number
** of available reader locks and should be at least 3. The default
** is SQLITE_SHM_NLOCK==8 and WAL_NREADER==5.
**
** Technically, the various VFSes are free to implement these locks however
** they see fit. However, compatibility is encouraged so that VFSes can
** interoperate. The standard implemention used on both unix and windows
** is for the index number to indicate a byte offset into the
** WalCkptInfo.aLock[] array in the wal-index header. In other words, all
** locks are on the shm file. The WALINDEX_LOCK_OFFSET constant (which
** should be 120) is the location in the shm file for the first locking
** byte.
*/
#define WAL_WRITE_LOCK 0
#define WAL_ALL_BUT_WRITE 1
#define WAL_CKPT_LOCK 1
#define WAL_RECOVER_LOCK 2
#define WAL_READ_LOCK(I) (3+(I))
#define WAL_NREADER (SQLITE_SHM_NLOCK-3)
/* Object declarations */
typedef struct WalIndexHdr WalIndexHdr;
typedef struct WalIterator WalIterator;
typedef struct WalCkptInfo WalCkptInfo;
/*
** The following object holds a copy of the wal-index header content.
**
** The actual header in the wal-index consists of two copies of this
** object followed by one instance of the WalCkptInfo object.
** For all versions of SQLite through 3.10.0 and probably beyond,
** the locking bytes (WalCkptInfo.aLock) start at offset 120 and
** the total header size is 136 bytes.
**
** The szPage value can be any power of 2 between 512 and 32768, inclusive.
** Or it can be 1 to represent a 65536-byte page. The latter case was
** added in 3.7.1 when support for 64K pages was added.
*/
struct WalIndexHdr {
u32 iVersion; /* Wal-index version */
u32 unused; /* Unused (padding) field */
u32 iChange; /* Counter incremented each transaction */
u8 isInit; /* 1 when initialized */
u8 bigEndCksum; /* True if checksums in WAL are big-endian */
u16 szPage; /* Database page size in bytes. 1==64K */
u32 mxFrame; /* Index of last valid frame in the WAL */
u32 nPage; /* Size of database in pages */
u32 aFrameCksum[2]; /* Checksum of last frame in log */
u32 aSalt[2]; /* Two salt values copied from WAL header */
u32 aCksum[2]; /* Checksum over all prior fields */
};
/*
** A copy of the following object occurs in the wal-index immediately
** following the second copy of the WalIndexHdr. This object stores
** information used by checkpoint.
**
** nBackfill is the number of frames in the WAL that have been written
** back into the database. (We call the act of moving content from WAL to
** database "backfilling".) The nBackfill number is never greater than
** WalIndexHdr.mxFrame. nBackfill can only be increased by threads
** holding the WAL_CKPT_LOCK lock (which includes a recovery thread).
** However, a WAL_WRITE_LOCK thread can move the value of nBackfill from
** mxFrame back to zero when the WAL is reset.
**
** nBackfillAttempted is the largest value of nBackfill that a checkpoint
** has attempted to achieve. Normally nBackfill==nBackfillAtempted, however
** the nBackfillAttempted is set before any backfilling is done and the
** nBackfill is only set after all backfilling completes. So if a checkpoint
** crashes, nBackfillAttempted might be larger than nBackfill. The
** WalIndexHdr.mxFrame must never be less than nBackfillAttempted.
**
** The aLock[] field is a set of bytes used for locking. These bytes should
** never be read or written.
**
** There is one entry in aReadMark[] for each reader lock. If a reader
** holds read-lock K, then the value in aReadMark[K] is no greater than
** the mxFrame for that reader. The value READMARK_NOT_USED (0xffffffff)
** for any aReadMark[] means that entry is unused. aReadMark[0] is
** a special case; its value is never used and it exists as a place-holder
** to avoid having to offset aReadMark[] indexs by one. Readers holding
** WAL_READ_LOCK(0) always ignore the entire WAL and read all content
** directly from the database.
**
** The value of aReadMark[K] may only be changed by a thread that
** is holding an exclusive lock on WAL_READ_LOCK(K). Thus, the value of
** aReadMark[K] cannot changed while there is a reader is using that mark
** since the reader will be holding a shared lock on WAL_READ_LOCK(K).
**
** The checkpointer may only transfer frames from WAL to database where
** the frame numbers are less than or equal to every aReadMark[] that is
** in use (that is, every aReadMark[j] for which there is a corresponding
** WAL_READ_LOCK(j)). New readers (usually) pick the aReadMark[] with the
** largest value and will increase an unused aReadMark[] to mxFrame if there
** is not already an aReadMark[] equal to mxFrame. The exception to the
** previous sentence is when nBackfill equals mxFrame (meaning that everything
** in the WAL has been backfilled into the database) then new readers
** will choose aReadMark[0] which has value 0 and hence such reader will
** get all their all content directly from the database file and ignore
** the WAL.
**
** Writers normally append new frames to the end of the WAL. However,
** if nBackfill equals mxFrame (meaning that all WAL content has been
** written back into the database) and if no readers are using the WAL
** (in other words, if there are no WAL_READ_LOCK(i) where i>0) then
** the writer will first "reset" the WAL back to the beginning and start
** writing new content beginning at frame 1.
**
** We assume that 32-bit loads are atomic and so no locks are needed in
** order to read from any aReadMark[] entries.
*/
struct WalCkptInfo {
u32 nBackfill; /* Number of WAL frames backfilled into DB */
u32 aReadMark[WAL_NREADER]; /* Reader marks */
u8 aLock[SQLITE_SHM_NLOCK]; /* Reserved space for locks */
u32 nBackfillAttempted; /* WAL frames perhaps written, or maybe not */
u32 notUsed0; /* Available for future enhancements */
};
#define READMARK_NOT_USED 0xffffffff
/* A block of WALINDEX_LOCK_RESERVED bytes beginning at
** WALINDEX_LOCK_OFFSET is reserved for locks. Since some systems
** only support mandatory file-locks, we do not read or write data
** from the region of the file on which locks are applied.
*/
#define WALINDEX_LOCK_OFFSET (sizeof(WalIndexHdr)*2+offsetof(WalCkptInfo,aLock))
#define WALINDEX_HDR_SIZE (sizeof(WalIndexHdr)*2+sizeof(WalCkptInfo))
/* Size of header before each frame in wal */
#define WAL_FRAME_HDRSIZE 24
/* Size of write ahead log header, including checksum. */
#define WAL_HDRSIZE 32
/* WAL magic value. Either this value, or the same value with the least
** significant bit also set (WAL_MAGIC | 0x00000001) is stored in 32-bit
** big-endian format in the first 4 bytes of a WAL file.
**
** If the LSB is set, then the checksums for each frame within the WAL
** file are calculated by treating all data as an array of 32-bit
** big-endian words. Otherwise, they are calculated by interpreting
** all data as 32-bit little-endian words.
*/
#define WAL_MAGIC 0x377f0682
/*
** Return the offset of frame iFrame in the write-ahead log file,
** assuming a database page size of szPage bytes. The offset returned
** is to the start of the write-ahead log frame-header.
*/
#define walFrameOffset(iFrame, szPage) ( \
WAL_HDRSIZE + ((iFrame)-1)*(i64)((szPage)+WAL_FRAME_HDRSIZE) \
)
/*
** An open write-ahead log file is represented by an instance of the
** following object.
*/
struct Wal {
sqlite3_vfs *pVfs; /* The VFS used to create pDbFd */
sqlite3_file *pDbFd; /* File handle for the database file */
sqlite3_file *pWalFd; /* File handle for WAL file */
u32 iCallback; /* Value to pass to log callback (or 0) */
i64 mxWalSize; /* Truncate WAL to this size upon reset */
int nWiData; /* Size of array apWiData */
int szFirstBlock; /* Size of first block written to WAL file */
volatile u32 **apWiData; /* Pointer to wal-index content in memory */
u32 szPage; /* Database page size */
i16 readLock; /* Which read lock is being held. -1 for none */
u8 syncFlags; /* Flags to use to sync header writes */
u8 exclusiveMode; /* Non-zero if connection is in exclusive mode */
u8 writeLock; /* True if in a write transaction */
u8 ckptLock; /* True if holding a checkpoint lock */
u8 readOnly; /* WAL_RDWR, WAL_RDONLY, or WAL_SHM_RDONLY */
u8 truncateOnCommit; /* True to truncate WAL file on commit */
u8 syncHeader; /* Fsync the WAL header if true */
u8 padToSectorBoundary; /* Pad transactions out to the next sector */
u8 bShmUnreliable; /* SHM content is read-only and unreliable */
WalIndexHdr hdr; /* Wal-index header for current transaction */
u32 minFrame; /* Ignore wal frames before this one */
u32 iReCksum; /* On commit, recalculate checksums from here */
const char *zWalName; /* Name of WAL file */
u32 nCkpt; /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
u8 lockError; /* True if a locking error has occurred */
#endif
#ifdef SQLITE_ENABLE_SNAPSHOT
WalIndexHdr *pSnapshot; /* Start transaction here if not NULL */
#endif
};
/*
** Candidate values for Wal.exclusiveMode.
*/
#define WAL_NORMAL_MODE 0
#define WAL_EXCLUSIVE_MODE 1
#define WAL_HEAPMEMORY_MODE 2
/*
** Possible values for WAL.readOnly
*/
#define WAL_RDWR 0 /* Normal read/write connection */
#define WAL_RDONLY 1 /* The WAL file is readonly */
#define WAL_SHM_RDONLY 2 /* The SHM file is readonly */
/*
** Each page of the wal-index mapping contains a hash-table made up of
** an array of HASHTABLE_NSLOT elements of the following type.
*/
typedef u16 ht_slot;
/*
** This structure is used to implement an iterator that loops through
** all frames in the WAL in database page order. Where two or more frames
** correspond to the same database page, the iterator visits only the
** frame most recently written to the WAL (in other words, the frame with
** the largest index).
**
** The internals of this structure are only accessed by:
**
** walIteratorInit() - Create a new iterator,
** walIteratorNext() - Step an iterator,
** walIteratorFree() - Free an iterator.
**
** This functionality is used by the checkpoint code (see walCheckpoint()).
*/
struct WalIterator {
int iPrior; /* Last result returned from the iterator */
int nSegment; /* Number of entries in aSegment[] */
struct WalSegment {
int iNext; /* Next slot in aIndex[] not yet returned */
ht_slot *aIndex; /* i0, i1, i2... such that aPgno[iN] ascend */
u32 *aPgno; /* Array of page numbers. */
int nEntry; /* Nr. of entries in aPgno[] and aIndex[] */
int iZero; /* Frame number associated with aPgno[0] */
} aSegment[1]; /* One for every 32KB page in the wal-index */
};
/*
** Define the parameters of the hash tables in the wal-index file. There
** is a hash-table following every HASHTABLE_NPAGE page numbers in the
** wal-index.
**
** Changing any of these constants will alter the wal-index format and
** create incompatibilities.
*/
#define HASHTABLE_NPAGE 4096 /* Must be power of 2 */
#define HASHTABLE_HASH_1 383 /* Should be prime */
#define HASHTABLE_NSLOT (HASHTABLE_NPAGE*2) /* Must be a power of 2 */
/*
** The block of page numbers associated with the first hash-table in a
** wal-index is smaller than usual. This is so that there is a complete
** hash-table on each aligned 32KB page of the wal-index.
*/
#define HASHTABLE_NPAGE_ONE (HASHTABLE_NPAGE - (WALINDEX_HDR_SIZE/sizeof(u32)))
/* The wal-index is divided into pages of WALINDEX_PGSZ bytes each. */
#define WALINDEX_PGSZ ( \
sizeof(ht_slot)*HASHTABLE_NSLOT + HASHTABLE_NPAGE*sizeof(u32) \
)
/*
** Obtain a pointer to the iPage'th page of the wal-index. The wal-index
** is broken into pages of WALINDEX_PGSZ bytes. Wal-index pages are
** numbered from zero.
**
** If the wal-index is currently smaller the iPage pages then the size
** of the wal-index might be increased, but only if it is safe to do
** so. It is safe to enlarge the wal-index if pWal->writeLock is true
** or pWal->exclusiveMode==WAL_HEAPMEMORY_MODE.
**
** If this call is successful, *ppPage is set to point to the wal-index
** page and SQLITE_OK is returned. If an error (an OOM or VFS error) occurs,
** then an SQLite error code is returned and *ppPage is set to 0.
*/
static int walIndexPage(Wal *pWal, int iPage, volatile u32 **ppPage){
int rc = SQLITE_OK;
/* Enlarge the pWal->apWiData[] array if required */
if( pWal->nWiData<=iPage ){
int nByte = sizeof(u32*)*(iPage+1);
volatile u32 **apNew;
apNew = (volatile u32 **)sqlite3_realloc64((void *)pWal->apWiData, nByte);
if( !apNew ){
*ppPage = 0;
return SQLITE_NOMEM_BKPT;
}
memset((void*)&apNew[pWal->nWiData], 0,
sizeof(u32*)*(iPage+1-pWal->nWiData));
pWal->apWiData = apNew;
pWal->nWiData = iPage+1;
}
/* Request a pointer to the required page from the VFS */
if( pWal->apWiData[iPage]==0 ){
if( pWal->exclusiveMode==WAL_HEAPMEMORY_MODE ){
pWal->apWiData[iPage] = (u32 volatile *)sqlite3MallocZero(WALINDEX_PGSZ);
if( !pWal->apWiData[iPage] ) rc = SQLITE_NOMEM_BKPT;
}else{
rc = sqlite3OsShmMap(pWal->pDbFd, iPage, WALINDEX_PGSZ,
pWal->writeLock, (void volatile **)&pWal->apWiData[iPage]
);
assert( pWal->apWiData[iPage]!=0 || rc!=SQLITE_OK || pWal->writeLock==0 );
testcase( pWal->apWiData[iPage]==0 && rc==SQLITE_OK );
if( (rc&0xff)==SQLITE_READONLY ){
pWal->readOnly |= WAL_SHM_RDONLY;
if( rc==SQLITE_READONLY ){
rc = SQLITE_OK;
}
}
}
}
*ppPage = pWal->apWiData[iPage];
assert( iPage==0 || *ppPage || rc!=SQLITE_OK );
return rc;
}
/*
** Return a pointer to the WalCkptInfo structure in the wal-index.
*/
static volatile WalCkptInfo *walCkptInfo(Wal *pWal){
assert( pWal->nWiData>0 && pWal->apWiData[0] );
return (volatile WalCkptInfo*)&(pWal->apWiData[0][sizeof(WalIndexHdr)/2]);
}
/*
** Return a pointer to the WalIndexHdr structure in the wal-index.
*/
static volatile WalIndexHdr *walIndexHdr(Wal *pWal){
assert( pWal->nWiData>0 && pWal->apWiData[0] );
return (volatile WalIndexHdr*)pWal->apWiData[0];
}
/*
** The argument to this macro must be of type u32. On a little-endian
** architecture, it returns the u32 value that results from interpreting
** the 4 bytes as a big-endian value. On a big-endian architecture, it
** returns the value that would be produced by interpreting the 4 bytes
** of the input value as a little-endian integer.
*/
#define BYTESWAP32(x) ( \
(((x)&0x000000FF)<<24) + (((x)&0x0000FF00)<<8) \
+ (((x)&0x00FF0000)>>8) + (((x)&0xFF000000)>>24) \
)
/*
** Generate or extend an 8 byte checksum based on the data in
** array aByte[] and the initial values of aIn[0] and aIn[1] (or
** initial values of 0 and 0 if aIn==NULL).
**
** The checksum is written back into aOut[] before returning.
**
** nByte must be a positive multiple of 8.
*/
static void walChecksumBytes(
int nativeCksum, /* True for native byte-order, false for non-native */
u8 *a, /* Content to be checksummed */
int nByte, /* Bytes of content in a[]. Must be a multiple of 8. */
const u32 *aIn, /* Initial checksum value input */
u32 *aOut /* OUT: Final checksum value output */
){
u32 s1, s2;
u32 *aData = (u32 *)a;
u32 *aEnd = (u32 *)&a[nByte];
if( aIn ){
s1 = aIn[0];
s2 = aIn[1];
}else{
s1 = s2 = 0;
}
assert( nByte>=8 );
assert( (nByte&0x00000007)==0 );
if( nativeCksum ){
do {
s1 += *aData++ + s2;
s2 += *aData++ + s1;
}while( aData<aEnd );
}else{
do {
s1 += BYTESWAP32(aData[0]) + s2;
s2 += BYTESWAP32(aData[1]) + s1;
aData += 2;
}while( aData<aEnd );
}
aOut[0] = s1;
aOut[1] = s2;
}
static void walShmBarrier(Wal *pWal){
if( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE ){
sqlite3OsShmBarrier(pWal->pDbFd);
}
}
/*
** Write the header information in pWal->hdr into the wal-index.
**
** The checksum on pWal->hdr is updated before it is written.
*/
static void walIndexWriteHdr(Wal *pWal){
volatile WalIndexHdr *aHdr = walIndexHdr(pWal);
const int nCksum = offsetof(WalIndexHdr, aCksum);
assert( pWal->writeLock );
pWal->hdr.isInit = 1;
pWal->hdr.iVersion = WALINDEX_MAX_VERSION;
walChecksumBytes(1, (u8*)&pWal->hdr, nCksum, 0, pWal->hdr.aCksum);
memcpy((void*)&aHdr[1], (const void*)&pWal->hdr, sizeof(WalIndexHdr));
walShmBarrier(pWal);
memcpy((void*)&aHdr[0], (const void*)&pWal->hdr, sizeof(WalIndexHdr));
}
/*
** This function encodes a single frame header and writes it to a buffer
** supplied by the caller. A frame-header is made up of a series of
** 4-byte big-endian integers, as follows:
**
** 0: Page number.
** 4: For commit records, the size of the database image in pages
** after the commit. For all other records, zero.
** 8: Salt-1 (copied from the wal-header)
** 12: Salt-2 (copied from the wal-header)
** 16: Checksum-1.
** 20: Checksum-2.
*/
static void walEncodeFrame(
Wal *pWal, /* The write-ahead log */
u32 iPage, /* Database page number for frame */
u32 nTruncate, /* New db size (or 0 for non-commit frames) */
u8 *aData, /* Pointer to page data */
u8 *aFrame /* OUT: Write encoded frame here */
){
int nativeCksum; /* True for native byte-order checksums */
u32 *aCksum = pWal->hdr.aFrameCksum;
assert( WAL_FRAME_HDRSIZE==24 );
sqlite3Put4byte(&aFrame[0], iPage);
sqlite3Put4byte(&aFrame[4], nTruncate);
if( pWal->iReCksum==0 ){
memcpy(&aFrame[8], pWal->hdr.aSalt, 8);
nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
sqlite3Put4byte(&aFrame[16], aCksum[0]);
sqlite3Put4byte(&aFrame[20], aCksum[1]);
}else{
memset(&aFrame[8], 0, 16);
}
}
/*
** Check to see if the frame with header in aFrame[] and content
** in aData[] is valid. If it is a valid frame, fill *piPage and
** *pnTruncate and return true. Return if the frame is not valid.
*/
static int walDecodeFrame(
Wal *pWal, /* The write-ahead log */
u32 *piPage, /* OUT: Database page number for frame */
u32 *pnTruncate, /* OUT: New db size (or 0 if not commit) */
u8 *aData, /* Pointer to page data (for checksum) */
u8 *aFrame /* Frame data */
){
int nativeCksum; /* True for native byte-order checksums */
u32 *aCksum = pWal->hdr.aFrameCksum;
u32 pgno; /* Page number of the frame */
assert( WAL_FRAME_HDRSIZE==24 );
/* A frame is only valid if the salt values in the frame-header
** match the salt values in the wal-header.
*/
if( memcmp(&pWal->hdr.aSalt, &aFrame[8], 8)!=0 ){
return 0;
}
/* A frame is only valid if the page number is creater than zero.
*/
pgno = sqlite3Get4byte(&aFrame[0]);
if( pgno==0 ){
return 0;
}
/* A frame is only valid if a checksum of the WAL header,
** all prior frams, the first 16 bytes of this frame-header,
** and the frame-data matches the checksum in the last 8
** bytes of this frame-header.
*/
nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
if( aCksum[0]!=sqlite3Get4byte(&aFrame[16])
|| aCksum[1]!=sqlite3Get4byte(&aFrame[20])
){
/* Checksum failed. */
return 0;
}
/* If we reach this point, the frame is valid. Return the page number
** and the new database size.
*/
*piPage = pgno;
*pnTruncate = sqlite3Get4byte(&aFrame[4]);
return 1;
}
#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
/*
** Names of locks. This routine is used to provide debugging output and is not
** a part of an ordinary build.
*/
static const char *walLockName(int lockIdx){
if( lockIdx==WAL_WRITE_LOCK ){
return "WRITE-LOCK";
}else if( lockIdx==WAL_CKPT_LOCK ){
return "CKPT-LOCK";
}else if( lockIdx==WAL_RECOVER_LOCK ){
return "RECOVER-LOCK";
}else{
static char zName[15];
sqlite3_snprintf(sizeof(zName), zName, "READ-LOCK[%d]",
lockIdx-WAL_READ_LOCK(0));
return zName;
}
}
#endif /*defined(SQLITE_TEST) || defined(SQLITE_DEBUG) */
/*
** Set or release locks on the WAL. Locks are either shared or exclusive.
** A lock cannot be moved directly between shared and exclusive - it must go
** through the unlocked state first.
**
** In locking_mode=EXCLUSIVE, all of these routines become no-ops.
*/
static int walLockShared(Wal *pWal, int lockIdx){
int rc;
if( pWal->exclusiveMode ) return SQLITE_OK;
rc = sqlite3OsShmLock(pWal->pDbFd, lockIdx, 1,
SQLITE_SHM_LOCK | SQLITE_SHM_SHARED);
WALTRACE(("WAL%p: acquire SHARED-%s %s\n", pWal,
walLockName(lockIdx), rc ? "failed" : "ok"));
VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && rc!=SQLITE_BUSY); )
return rc;
}
static void walUnlockShared(Wal *pWal, int lockIdx){
if( pWal->exclusiveMode ) return;
(void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, 1,
SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED);
WALTRACE(("WAL%p: release SHARED-%s\n", pWal, walLockName(lockIdx)));
}
static int walLockExclusive(Wal *pWal, int lockIdx, int n){
int rc;
if( pWal->exclusiveMode ) return SQLITE_OK;
rc = sqlite3OsShmLock(pWal->pDbFd, lockIdx, n,
SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE);
WALTRACE(("WAL%p: acquire EXCLUSIVE-%s cnt=%d %s\n", pWal,
walLockName(lockIdx), n, rc ? "failed" : "ok"));
VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && rc!=SQLITE_BUSY); )
return rc;
}
static void walUnlockExclusive(Wal *pWal, int lockIdx, int n){
if( pWal->exclusiveMode ) return;
(void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, n,
SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE);
WALTRACE(("WAL%p: release EXCLUSIVE-%s cnt=%d\n", pWal,
walLockName(lockIdx), n));
}
/*
** Compute a hash on a page number. The resulting hash value must land
** between 0 and (HASHTABLE_NSLOT-1). The walHashNext() function advances
** the hash to the next value in the event of a collision.
*/
static int walHash(u32 iPage){
assert( iPage>0 );
assert( (HASHTABLE_NSLOT & (HASHTABLE_NSLOT-1))==0 );
return (iPage*HASHTABLE_HASH_1) & (HASHTABLE_NSLOT-1);
}
static int walNextHash(int iPriorHash){
return (iPriorHash+1)&(HASHTABLE_NSLOT-1);
}
/*
** Return pointers to the hash table and page number array stored on
** page iHash of the wal-index. The wal-index is broken into 32KB pages
** numbered starting from 0.
**
** Set output variable *paHash to point to the start of the hash table
** in the wal-index file. Set *piZero to one less than the frame
** number of the first frame indexed by this hash table. If a
** slot in the hash table is set to N, it refers to frame number
** (*piZero+N) in the log.
**
** Finally, set *paPgno so that *paPgno[1] is the page number of the
** first frame indexed by the hash table, frame (*piZero+1).
*/
static int walHashGet(
Wal *pWal, /* WAL handle */
int iHash, /* Find the iHash'th table */
volatile ht_slot **paHash, /* OUT: Pointer to hash index */
volatile u32 **paPgno, /* OUT: Pointer to page number array */
u32 *piZero /* OUT: Frame associated with *paPgno[0] */
){
int rc; /* Return code */
volatile u32 *aPgno;
rc = walIndexPage(pWal, iHash, &aPgno);
assert( rc==SQLITE_OK || iHash>0 );
if( rc==SQLITE_OK ){
u32 iZero;
volatile ht_slot *aHash;
aHash = (volatile ht_slot *)&aPgno[HASHTABLE_NPAGE];
if( iHash==0 ){
aPgno = &aPgno[WALINDEX_HDR_SIZE/sizeof(u32)];
iZero = 0;
}else{
iZero = HASHTABLE_NPAGE_ONE + (iHash-1)*HASHTABLE_NPAGE;
}
*paPgno = &aPgno[-1];
*paHash = aHash;
*piZero = iZero;
}
return rc;
}
/*
** Return the number of the wal-index page that contains the hash-table
** and page-number array that contain entries corresponding to WAL frame
** iFrame. The wal-index is broken up into 32KB pages. Wal-index pages
** are numbered starting from 0.
*/
static int walFramePage(u32 iFrame){
int iHash = (iFrame+HASHTABLE_NPAGE-HASHTABLE_NPAGE_ONE-1) / HASHTABLE_NPAGE;
assert( (iHash==0 || iFrame>HASHTABLE_NPAGE_ONE)
&& (iHash>=1 || iFrame<=HASHTABLE_NPAGE_ONE)
&& (iHash<=1 || iFrame>(HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE))
&& (iHash>=2 || iFrame<=HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE)
&& (iHash<=2 || iFrame>(HASHTABLE_NPAGE_ONE+2*HASHTABLE_NPAGE))
);
return iHash;
}
/*
** Return the page number associated with frame iFrame in this WAL.
*/
static u32 walFramePgno(Wal *pWal, u32 iFrame){
int iHash = walFramePage(iFrame);
if( iHash==0 ){
return pWal->apWiData[0][WALINDEX_HDR_SIZE/sizeof(u32) + iFrame - 1];
}
return pWal->apWiData[iHash][(iFrame-1-HASHTABLE_NPAGE_ONE)%HASHTABLE_NPAGE];
}
/*
** Remove entries from the hash table that point to WAL slots greater
** than pWal->hdr.mxFrame.
**
** This function is called whenever pWal->hdr.mxFrame is decreased due
** to a rollback or savepoint.
**
** At most only the hash table containing pWal->hdr.mxFrame needs to be
** updated. Any later hash tables will be automatically cleared when
** pWal->hdr.mxFrame advances to the point where those hash tables are
** actually needed.
*/
static void walCleanupHash(Wal *pWal){
volatile ht_slot *aHash = 0; /* Pointer to hash table to clear */
volatile u32 *aPgno = 0; /* Page number array for hash table */
u32 iZero = 0; /* frame == (aHash[x]+iZero) */
int iLimit = 0; /* Zero values greater than this */
int nByte; /* Number of bytes to zero in aPgno[] */
int i; /* Used to iterate through aHash[] */
assert( pWal->writeLock );
testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE-1 );
testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE );
testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE+1 );
if( pWal->hdr.mxFrame==0 ) return;
/* Obtain pointers to the hash-table and page-number array containing
** the entry that corresponds to frame pWal->hdr.mxFrame. It is guaranteed
** that the page said hash-table and array reside on is already mapped.
*/
assert( pWal->nWiData>walFramePage(pWal->hdr.mxFrame) );
assert( pWal->apWiData[walFramePage(pWal->hdr.mxFrame)] );
walHashGet(pWal, walFramePage(pWal->hdr.mxFrame), &aHash, &aPgno, &iZero);
/* Zero all hash-table entries that correspond to frame numbers greater
** than pWal->hdr.mxFrame.
*/
iLimit = pWal->hdr.mxFrame - iZero;
assert( iLimit>0 );
for(i=0; i<HASHTABLE_NSLOT; i++){
if( aHash[i]>iLimit ){
aHash[i] = 0;
}
}
/* Zero the entries in the aPgno array that correspond to frames with
** frame numbers greater than pWal->hdr.mxFrame.
*/
nByte = (int)((char *)aHash - (char *)&aPgno[iLimit+1]);
memset((void *)&aPgno[iLimit+1], 0, nByte);
#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
/* Verify that the every entry in the mapping region is still reachable
** via the hash table even after the cleanup.
*/
if( iLimit ){
int j; /* Loop counter */
int iKey; /* Hash key */
for(j=1; j<=iLimit; j++){
for(iKey=walHash(aPgno[j]); aHash[iKey]; iKey=walNextHash(iKey)){
if( aHash[iKey]==j ) break;
}
assert( aHash[iKey]==j );
}
}
#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */
}
/*
** Set an entry in the wal-index that will map database page number
** pPage into WAL frame iFrame.
*/
static int walIndexAppend(Wal *pWal, u32 iFrame, u32 iPage){
int rc; /* Return code */
u32 iZero = 0; /* One less than frame number of aPgno[1] */
volatile u32 *aPgno = 0; /* Page number array */
volatile ht_slot *aHash = 0; /* Hash table */
rc = walHashGet(pWal, walFramePage(iFrame), &aHash, &aPgno, &iZero);
/* Assuming the wal-index file was successfully mapped, populate the
** page number array and hash table entry.
*/
if( rc==SQLITE_OK ){
int iKey; /* Hash table key */
int idx; /* Value to write to hash-table slot */
int nCollide; /* Number of hash collisions */
idx = iFrame - iZero;
assert( idx <= HASHTABLE_NSLOT/2 + 1 );
/* If this is the first entry to be added to this hash-table, zero the
** entire hash table and aPgno[] array before proceeding.
*/
if( idx==1 ){
int nByte = (int)((u8 *)&aHash[HASHTABLE_NSLOT] - (u8 *)&aPgno[1]);
memset((void*)&aPgno[1], 0, nByte);
}
/* If the entry in aPgno[] is already set, then the previous writer
** must have exited unexpectedly in the middle of a transaction (after
** writing one or more dirty pages to the WAL to free up memory).
** Remove the remnants of that writers uncommitted transaction from
** the hash-table before writing any new entries.
*/
if( aPgno[idx] ){
walCleanupHash(pWal);
assert( !aPgno[idx] );
}
/* Write the aPgno[] array entry and the hash-table slot. */
nCollide = idx;
for(iKey=walHash(iPage); aHash[iKey]; iKey=walNextHash(iKey)){
if( (nCollide--)==0 ) return SQLITE_CORRUPT_BKPT;
}
aPgno[idx] = iPage;
aHash[iKey] = (ht_slot)idx;
#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
/* Verify that the number of entries in the hash table exactly equals
** the number of entries in the mapping region.
*/
{
int i; /* Loop counter */
int nEntry = 0; /* Number of entries in the hash table */
for(i=0; i<HASHTABLE_NSLOT; i++){ if( aHash[i] ) nEntry++; }
assert( nEntry==idx );
}
/* Verify that the every entry in the mapping region is reachable
** via the hash table. This turns out to be a really, really expensive
** thing to check, so only do this occasionally - not on every
** iteration.
*/
if( (idx&0x3ff)==0 ){
int i; /* Loop counter */
for(i=1; i<=idx; i++){
for(iKey=walHash(aPgno[i]); aHash[iKey]; iKey=walNextHash(iKey)){
if( aHash[iKey]==i ) break;
}
assert( aHash[iKey]==i );
}
}
#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */
}
return rc;
}
/*
** Recover the wal-index by reading the write-ahead log file.
**
** This routine first tries to establish an exclusive lock on the
** wal-index to prevent other threads/processes from doing anything
** with the WAL or wal-index while recovery is running. The
** WAL_RECOVER_LOCK is also held so that other threads will know
** that this thread is running recovery. If unable to establish
** the necessary locks, this routine returns SQLITE_BUSY.
*/
static int walIndexRecover(Wal *pWal){
int rc; /* Return Code */
i64 nSize; /* Size of log file */
u32 aFrameCksum[2] = {0, 0};
int iLock; /* Lock offset to lock for checkpoint */
/* Obtain an exclusive lock on all byte in the locking range not already
** locked by the caller. The caller is guaranteed to have locked the
** WAL_WRITE_LOCK byte, and may have also locked the WAL_CKPT_LOCK byte.
** If successful, the same bytes that are locked here are unlocked before
** this function returns.
*/
assert( pWal->ckptLock==1 || pWal->ckptLock==0 );
assert( WAL_ALL_BUT_WRITE==WAL_WRITE_LOCK+1 );
assert( WAL_CKPT_LOCK==WAL_ALL_BUT_WRITE );
assert( pWal->writeLock );
iLock = WAL_ALL_BUT_WRITE + pWal->ckptLock;
rc = walLockExclusive(pWal, iLock, WAL_READ_LOCK(0)-iLock);
if( rc==SQLITE_OK ){
rc = walLockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
if( rc!=SQLITE_OK ){
walUnlockExclusive(pWal, iLock, WAL_READ_LOCK(0)-iLock);
}
}
if( rc ){
return rc;
}
WALTRACE(("WAL%p: recovery begin...\n", pWal));
memset(&pWal->hdr, 0, sizeof(WalIndexHdr));
rc = sqlite3OsFileSize(pWal->pWalFd, &nSize);
if( rc!=SQLITE_OK ){
goto recovery_error;
}
if( nSize>WAL_HDRSIZE ){
u8 aBuf[WAL_HDRSIZE]; /* Buffer to load WAL header into */
u8 *aFrame = 0; /* Malloc'd buffer to load entire frame */
int szFrame; /* Number of bytes in buffer aFrame[] */
u8 *aData; /* Pointer to data part of aFrame buffer */
int iFrame; /* Index of last frame read */
i64 iOffset; /* Next offset to read from log file */
int szPage; /* Page size according to the log */
u32 magic; /* Magic value read from WAL header */
u32 version; /* Magic value read from WAL header */
int isValid; /* True if this frame is valid */
/* Read in the WAL header. */
rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0);
if( rc!=SQLITE_OK ){
goto recovery_error;
}
/* If the database page size is not a power of two, or is greater than
** SQLITE_MAX_PAGE_SIZE, conclude that the WAL file contains no valid
** data. Similarly, if the 'magic' value is invalid, ignore the whole
** WAL file.
*/
magic = sqlite3Get4byte(&aBuf[0]);
szPage = sqlite3Get4byte(&aBuf[8]);
if( (magic&0xFFFFFFFE)!=WAL_MAGIC
|| szPage&(szPage-1)
|| szPage>SQLITE_MAX_PAGE_SIZE
|| szPage<512
){
goto finished;
}
pWal->hdr.bigEndCksum = (u8)(magic&0x00000001);
pWal->szPage = szPage;
pWal->nCkpt = sqlite3Get4byte(&aBuf[12]);
memcpy(&pWal->hdr.aSalt, &aBuf[16], 8);
/* Verify that the WAL header checksum is correct */
walChecksumBytes(pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN,
aBuf, WAL_HDRSIZE-2*4, 0, pWal->hdr.aFrameCksum
);
if( pWal->hdr.aFrameCksum[0]!=sqlite3Get4byte(&aBuf[24])
|| pWal->hdr.aFrameCksum[1]!=sqlite3Get4byte(&aBuf[28])
){
goto finished;
}
/* Verify that the version number on the WAL format is one that
** are able to understand */
version = sqlite3Get4byte(&aBuf[4]);
if( version!=WAL_MAX_VERSION ){
rc = SQLITE_CANTOPEN_BKPT;
goto finished;
}
/* Malloc a buffer to read frames into. */
szFrame = szPage + WAL_FRAME_HDRSIZE;
aFrame = (u8 *)sqlite3_malloc64(szFrame);
if( !aFrame ){
rc = SQLITE_NOMEM_BKPT;
goto recovery_error;
}
aData = &aFrame[WAL_FRAME_HDRSIZE];
/* Read all frames from the log file. */
iFrame = 0;
for(iOffset=WAL_HDRSIZE; (iOffset+szFrame)<=nSize; iOffset+=szFrame){
u32 pgno; /* Database page number for frame */
u32 nTruncate; /* dbsize field from frame header */
/* Read and decode the next log frame. */
iFrame++;
rc = sqlite3OsRead(pWal->pWalFd, aFrame, szFrame, iOffset);
if( rc!=SQLITE_OK ) break;
isValid = walDecodeFrame(pWal, &pgno, &nTruncate, aData, aFrame);
if( !isValid ) break;
rc = walIndexAppend(pWal, iFrame, pgno);
if( rc!=SQLITE_OK ) break;
/* If nTruncate is non-zero, this is a commit record. */
if( nTruncate ){
pWal->hdr.mxFrame = iFrame;
pWal->hdr.nPage = nTruncate;
pWal->hdr.szPage = (u16)((szPage&0xff00) | (szPage>>16));
testcase( szPage<=32768 );
testcase( szPage>=65536 );
aFrameCksum[0] = pWal->hdr.aFrameCksum[0];
aFrameCksum[1] = pWal->hdr.aFrameCksum[1];
}
}
sqlite3_free(aFrame);
}
finished:
if( rc==SQLITE_OK ){
volatile WalCkptInfo *pInfo;
int i;
pWal->hdr.aFrameCksum[0] = aFrameCksum[0];
pWal->hdr.aFrameCksum[1] = aFrameCksum[1];
walIndexWriteHdr(pWal);
/* Reset the checkpoint-header. This is safe because this thread is
** currently holding locks that exclude all other readers, writers and
** checkpointers.
*/
pInfo = walCkptInfo(pWal);
pInfo->nBackfill = 0;
pInfo->nBackfillAttempted = pWal->hdr.mxFrame;
pInfo->aReadMark[0] = 0;
for(i=1; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
if( pWal->hdr.mxFrame ) pInfo->aReadMark[1] = pWal->hdr.mxFrame;
/* If more than one frame was recovered from the log file, report an
** event via sqlite3_log(). This is to help with identifying performance
** problems caused by applications routinely shutting down without
** checkpointing the log file.
*/
if( pWal->hdr.nPage ){
sqlite3_log(SQLITE_NOTICE_RECOVER_WAL,
"recovered %d frames from WAL file %s",
pWal->hdr.mxFrame, pWal->zWalName
);
}
}
recovery_error:
WALTRACE(("WAL%p: recovery %s\n", pWal, rc ? "failed" : "ok"));
walUnlockExclusive(pWal, iLock, WAL_READ_LOCK(0)-iLock);
walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
return rc;
}
/*
** Close an open wal-index.
*/
static void walIndexClose(Wal *pWal, int isDelete){
if( pWal->exclusiveMode==WAL_HEAPMEMORY_MODE || pWal->bShmUnreliable ){
int i;
for(i=0; i<pWal->nWiData; i++){
sqlite3_free((void *)pWal->apWiData[i]);
pWal->apWiData[i] = 0;
}
}
if( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE ){
sqlite3OsShmUnmap(pWal->pDbFd, isDelete);
}
}
/*
** Open a connection to the WAL file zWalName. The database file must
** already be opened on connection pDbFd. The buffer that zWalName points
** to must remain valid for the lifetime of the returned Wal* handle.
**
** A SHARED lock should be held on the database file when this function
** is called. The purpose of this SHARED lock is to prevent any other
** client from unlinking the WAL or wal-index file. If another process
** were to do this just after this client opened one of these files, the
** system would be badly broken.
**
** If the log file is successfully opened, SQLITE_OK is returned and
** *ppWal is set to point to a new WAL handle. If an error occurs,
** an SQLite error code is returned and *ppWal is left unmodified.
*/
int sqlite3WalOpen(
sqlite3_vfs *pVfs, /* vfs module to open wal and wal-index */
sqlite3_file *pDbFd, /* The open database file */
const char *zWalName, /* Name of the WAL file */
int bNoShm, /* True to run in heap-memory mode */
i64 mxWalSize, /* Truncate WAL to this size on reset */
Wal **ppWal /* OUT: Allocated Wal handle */
){
int rc; /* Return Code */
Wal *pRet; /* Object to allocate and return */
int flags; /* Flags passed to OsOpen() */
assert( zWalName && zWalName[0] );
assert( pDbFd );
/* In the amalgamation, the os_unix.c and os_win.c source files come before
** this source file. Verify that the #defines of the locking byte offsets
** in os_unix.c and os_win.c agree with the WALINDEX_LOCK_OFFSET value.
** For that matter, if the lock offset ever changes from its initial design
** value of 120, we need to know that so there is an assert() to check it.
*/
assert( 120==WALINDEX_LOCK_OFFSET );
assert( 136==WALINDEX_HDR_SIZE );
#ifdef WIN_SHM_BASE
assert( WIN_SHM_BASE==WALINDEX_LOCK_OFFSET );
#endif
#ifdef UNIX_SHM_BASE
assert( UNIX_SHM_BASE==WALINDEX_LOCK_OFFSET );
#endif
/* Allocate an instance of struct Wal to return. */
*ppWal = 0;
pRet = (Wal*)sqlite3MallocZero(sizeof(Wal) + pVfs->szOsFile);
if( !pRet ){
return SQLITE_NOMEM_BKPT;
}
pRet->pVfs = pVfs;
pRet->pWalFd = (sqlite3_file *)&pRet[1];
pRet->pDbFd = pDbFd;
pRet->readLock = -1;
pRet->mxWalSize = mxWalSize;
pRet->zWalName = zWalName;
pRet->syncHeader = 1;
pRet->padToSectorBoundary = 1;
pRet->exclusiveMode = (bNoShm ? WAL_HEAPMEMORY_MODE: WAL_NORMAL_MODE);
/* Open file handle on the write-ahead log file. */
flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_WAL);
rc = sqlite3OsOpen(pVfs, zWalName, pRet->pWalFd, flags, &flags);
if( rc==SQLITE_OK && flags&SQLITE_OPEN_READONLY ){
pRet->readOnly = WAL_RDONLY;
}
if( rc!=SQLITE_OK ){
walIndexClose(pRet, 0);
sqlite3OsClose(pRet->pWalFd);
sqlite3_free(pRet);
}else{
int iDC = sqlite3OsDeviceCharacteristics(pDbFd);
if( iDC & SQLITE_IOCAP_SEQUENTIAL ){ pRet->syncHeader = 0; }
if( iDC & SQLITE_IOCAP_POWERSAFE_OVERWRITE ){
pRet->padToSectorBoundary = 0;
}
*ppWal = pRet;
WALTRACE(("WAL%d: opened\n", pRet));
}
return rc;
}
/*
** Change the size to which the WAL file is trucated on each reset.
*/
void sqlite3WalLimit(Wal *pWal, i64 iLimit){
if( pWal ) pWal->mxWalSize = iLimit;
}
/*
** Find the smallest page number out of all pages held in the WAL that
** has not been returned by any prior invocation of this method on the
** same WalIterator object. Write into *piFrame the frame index where
** that page was last written into the WAL. Write into *piPage the page
** number.
**
** Return 0 on success. If there are no pages in the WAL with a page
** number larger than *piPage, then return 1.
*/
static int walIteratorNext(
WalIterator *p, /* Iterator */
u32 *piPage, /* OUT: The page number of the next page */
u32 *piFrame /* OUT: Wal frame index of next page */
){
u32 iMin; /* Result pgno must be greater than iMin */
u32 iRet = 0xFFFFFFFF; /* 0xffffffff is never a valid page number */
int i; /* For looping through segments */
iMin = p->iPrior;
assert( iMin<0xffffffff );
for(i=p->nSegment-1; i>=0; i--){
struct WalSegment *pSegment = &p->aSegment[i];
while( pSegment->iNext<pSegment->nEntry ){
u32 iPg = pSegment->aPgno[pSegment->aIndex[pSegment->iNext]];
if( iPg>iMin ){
if( iPg<iRet ){
iRet = iPg;
*piFrame = pSegment->iZero + pSegment->aIndex[pSegment->iNext];
}
break;
}
pSegment->iNext++;
}
}
*piPage = p->iPrior = iRet;
return (iRet==0xFFFFFFFF);
}
/*
** This function merges two sorted lists into a single sorted list.
**
** aLeft[] and aRight[] are arrays of indices. The sort key is
** aContent[aLeft[]] and aContent[aRight[]]. Upon entry, the following
** is guaranteed for all J<K:
**
** aContent[aLeft[J]] < aContent[aLeft[K]]
** aContent[aRight[J]] < aContent[aRight[K]]
**
** This routine overwrites aRight[] with a new (probably longer) sequence
** of indices such that the aRight[] contains every index that appears in
** either aLeft[] or the old aRight[] and such that the second condition
** above is still met.
**
** The aContent[aLeft[X]] values will be unique for all X. And the
** aContent[aRight[X]] values will be unique too. But there might be
** one or more combinations of X and Y such that
**
** aLeft[X]!=aRight[Y] && aContent[aLeft[X]] == aContent[aRight[Y]]
**
** When that happens, omit the aLeft[X] and use the aRight[Y] index.
*/
static void walMerge(
const u32 *aContent, /* Pages in wal - keys for the sort */
ht_slot *aLeft, /* IN: Left hand input list */
int nLeft, /* IN: Elements in array *paLeft */
ht_slot **paRight, /* IN/OUT: Right hand input list */
int *pnRight, /* IN/OUT: Elements in *paRight */
ht_slot *aTmp /* Temporary buffer */
){
int iLeft = 0; /* Current index in aLeft */
int iRight = 0; /* Current index in aRight */
int iOut = 0; /* Current index in output buffer */
int nRight = *pnRight;
ht_slot *aRight = *paRight;
assert( nLeft>0 && nRight>0 );
while( iRight<nRight || iLeft<nLeft ){
ht_slot logpage;
Pgno dbpage;
if( (iLeft<nLeft)
&& (iRight>=nRight || aContent[aLeft[iLeft]]<aContent[aRight[iRight]])
){
logpage = aLeft[iLeft++];
}else{
logpage = aRight[iRight++];
}
dbpage = aContent[logpage];
aTmp[iOut++] = logpage;
if( iLeft<nLeft && aContent[aLeft[iLeft]]==dbpage ) iLeft++;
assert( iLeft>=nLeft || aContent[aLeft[iLeft]]>dbpage );
assert( iRight>=nRight || aContent[aRight[iRight]]>dbpage );
}
*paRight = aLeft;
*pnRight = iOut;
memcpy(aLeft, aTmp, sizeof(aTmp[0])*iOut);
}
/*
** Sort the elements in list aList using aContent[] as the sort key.
** Remove elements with duplicate keys, preferring to keep the
** larger aList[] values.
**
** The aList[] entries are indices into aContent[]. The values in
** aList[] are to be sorted so that for all J<K:
**
** aContent[aList[J]] < aContent[aList[K]]
**
** For any X and Y such that
**
** aContent[aList[X]] == aContent[aList[Y]]
**
** Keep the larger of the two values aList[X] and aList[Y] and discard
** the smaller.
*/
static void walMergesort(
const u32 *aContent, /* Pages in wal */
ht_slot *aBuffer, /* Buffer of at least *pnList items to use */
ht_slot *aList, /* IN/OUT: List to sort */
int *pnList /* IN/OUT: Number of elements in aList[] */
){
struct Sublist {
int nList; /* Number of elements in aList */
ht_slot *aList; /* Pointer to sub-list content */
};
const int nList = *pnList; /* Size of input list */
int nMerge = 0; /* Number of elements in list aMerge */
ht_slot *aMerge = 0; /* List to be merged */
int iList; /* Index into input list */
u32 iSub = 0; /* Index into aSub array */
struct Sublist aSub[13]; /* Array of sub-lists */
memset(aSub, 0, sizeof(aSub));
assert( nList<=HASHTABLE_NPAGE && nList>0 );
assert( HASHTABLE_NPAGE==(1<<(ArraySize(aSub)-1)) );
for(iList=0; iList<nList; iList++){
nMerge = 1;
aMerge = &aList[iList];
for(iSub=0; iList & (1<<iSub); iSub++){
struct Sublist *p;
assert( iSub<ArraySize(aSub) );
p = &aSub[iSub];
assert( p->aList && p->nList<=(1<<iSub) );
assert( p->aList==&aList[iList&~((2<<iSub)-1)] );
walMerge(aContent, p->aList, p->nList, &aMerge, &nMerge, aBuffer);
}
aSub[iSub].aList = aMerge;
aSub[iSub].nList = nMerge;
}
for(iSub++; iSub<ArraySize(aSub); iSub++){
if( nList & (1<<iSub) ){
struct Sublist *p;
assert( iSub<ArraySize(aSub) );
p = &aSub[iSub];
assert( p->nList<=(1<<iSub) );
assert( p->aList==&aList[nList&~((2<<iSub)-1)] );
walMerge(aContent, p->aList, p->nList, &aMerge, &nMerge, aBuffer);
}
}
assert( aMerge==aList );
*pnList = nMerge;
#ifdef SQLITE_DEBUG
{
int i;
for(i=1; i<*pnList; i++){
assert( aContent[aList[i]] > aContent[aList[i-1]] );
}
}
#endif
}
/*
** Free an iterator allocated by walIteratorInit().
*/
static void walIteratorFree(WalIterator *p){
sqlite3_free(p);
}
/*
** Construct a WalInterator object that can be used to loop over all
** pages in the WAL in ascending order. The caller must hold the checkpoint
** lock.
**
** On success, make *pp point to the newly allocated WalInterator object
** return SQLITE_OK. Otherwise, return an error code. If this routine
** returns an error, the value of *pp is undefined.
**
** The calling routine should invoke walIteratorFree() to destroy the
** WalIterator object when it has finished with it.
*/
static int walIteratorInit(Wal *pWal, WalIterator **pp){
WalIterator *p; /* Return value */
int nSegment; /* Number of segments to merge */
u32 iLast; /* Last frame in log */
int nByte; /* Number of bytes to allocate */
int i; /* Iterator variable */
ht_slot *aTmp; /* Temp space used by merge-sort */
int rc = SQLITE_OK; /* Return Code */
/* This routine only runs while holding the checkpoint lock. And
** it only runs if there is actually content in the log (mxFrame>0).
*/
assert( pWal->ckptLock && pWal->hdr.mxFrame>0 );
iLast = pWal->hdr.mxFrame;
/* Allocate space for the WalIterator object. */
nSegment = walFramePage(iLast) + 1;
nByte = sizeof(WalIterator)
+ (nSegment-1)*sizeof(struct WalSegment)
+ iLast*sizeof(ht_slot);
p = (WalIterator *)sqlite3_malloc64(nByte);
if( !p ){
return SQLITE_NOMEM_BKPT;
}
memset(p, 0, nByte);
p->nSegment = nSegment;
/* Allocate temporary space used by the merge-sort routine. This block
** of memory will be freed before this function returns.
*/
aTmp = (ht_slot *)sqlite3_malloc64(
sizeof(ht_slot) * (iLast>HASHTABLE_NPAGE?HASHTABLE_NPAGE:iLast)
);
if( !aTmp ){
rc = SQLITE_NOMEM_BKPT;
}
for(i=0; rc==SQLITE_OK && i<nSegment; i++){
volatile ht_slot *aHash;
u32 iZero;
volatile u32 *aPgno;
rc = walHashGet(pWal, i, &aHash, &aPgno, &iZero);
if( rc==SQLITE_OK ){
int j; /* Counter variable */
int nEntry; /* Number of entries in this segment */
ht_slot *aIndex; /* Sorted index for this segment */
aPgno++;
if( (i+1)==nSegment ){
nEntry = (int)(iLast - iZero);
}else{
nEntry = (int)((u32*)aHash - (u32*)aPgno);
}
aIndex = &((ht_slot *)&p->aSegment[p->nSegment])[iZero];
iZero++;
for(j=0; j<nEntry; j++){
aIndex[j] = (ht_slot)j;
}
walMergesort((u32 *)aPgno, aTmp, aIndex, &nEntry);
p->aSegment[i].iZero = iZero;
p->aSegment[i].nEntry = nEntry;
p->aSegment[i].aIndex = aIndex;
p->aSegment[i].aPgno = (u32 *)aPgno;
}
}
sqlite3_free(aTmp);
if( rc!=SQLITE_OK ){
walIteratorFree(p);
}
*pp = p;
return rc;
}
/*
** Attempt to obtain the exclusive WAL lock defined by parameters lockIdx and
** n. If the attempt fails and parameter xBusy is not NULL, then it is a
** busy-handler function. Invoke it and retry the lock until either the
** lock is successfully obtained or the busy-handler returns 0.
*/
static int walBusyLock(
Wal *pWal, /* WAL connection */
int (*xBusy)(void*), /* Function to call when busy */
void *pBusyArg, /* Context argument for xBusyHandler */
int lockIdx, /* Offset of first byte to lock */
int n /* Number of bytes to lock */
){
int rc;
do {
rc = walLockExclusive(pWal, lockIdx, n);
}while( xBusy && rc==SQLITE_BUSY && xBusy(pBusyArg) );
return rc;
}
/*
** The cache of the wal-index header must be valid to call this function.
** Return the page-size in bytes used by the database.
*/
static int walPagesize(Wal *pWal){
return (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16);
}
/*
** The following is guaranteed when this function is called:
**
** a) the WRITER lock is held,
** b) the entire log file has been checkpointed, and
** c) any existing readers are reading exclusively from the database
** file - there are no readers that may attempt to read a frame from
** the log file.
**
** This function updates the shared-memory structures so that the next
** client to write to the database (which may be this one) does so by
** writing frames into the start of the log file.
**
** The value of parameter salt1 is used as the aSalt[1] value in the
** new wal-index header. It should be passed a pseudo-random value (i.e.
** one obtained from sqlite3_randomness()).
*/
static void walRestartHdr(Wal *pWal, u32 salt1){
volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
int i; /* Loop counter */
u32 *aSalt = pWal->hdr.aSalt; /* Big-endian salt values */
pWal->nCkpt++;
pWal->hdr.mxFrame = 0;
sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0]));
memcpy(&pWal->hdr.aSalt[1], &salt1, 4);
walIndexWriteHdr(pWal);
pInfo->nBackfill = 0;
pInfo->nBackfillAttempted = 0;
pInfo->aReadMark[1] = 0;
for(i=2; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
assert( pInfo->aReadMark[0]==0 );
}
/*
** Copy as much content as we can from the WAL back into the database file
** in response to an sqlite3_wal_checkpoint() request or the equivalent.
**
** The amount of information copies from WAL to database might be limited
** by active readers. This routine will never overwrite a database page
** that a concurrent reader might be using.
**
** All I/O barrier operations (a.k.a fsyncs) occur in this routine when
** SQLite is in WAL-mode in synchronous=NORMAL. That means that if
** checkpoints are always run by a background thread or background
** process, foreground threads will never block on a lengthy fsync call.
**
** Fsync is called on the WAL before writing content out of the WAL and
** into the database. This ensures that if the new content is persistent
** in the WAL and can be recovered following a power-loss or hard reset.
**
** Fsync is also called on the database file if (and only if) the entire
** WAL content is copied into the database file. This second fsync makes
** it safe to delete the WAL since the new content will persist in the
** database file.
**
** This routine uses and updates the nBackfill field of the wal-index header.
** This is the only routine that will increase the value of nBackfill.
** (A WAL reset or recovery will revert nBackfill to zero, but not increase
** its value.)
**
** The caller must be holding sufficient locks to ensure that no other
** checkpoint is running (in any other thread or process) at the same
** time.
*/
static int walCheckpoint(
Wal *pWal, /* Wal connection */
sqlite3 *db, /* Check for interrupts on this handle */
int eMode, /* One of PASSIVE, FULL or RESTART */
int (*xBusy)(void*), /* Function to call when busy */
void *pBusyArg, /* Context argument for xBusyHandler */
int sync_flags, /* Flags for OsSync() (or 0) */
u8 *zBuf /* Temporary buffer to use */
){
int rc = SQLITE_OK; /* Return code */
int szPage; /* Database page-size */
WalIterator *pIter = 0; /* Wal iterator context */
u32 iDbpage = 0; /* Next database page to write */
u32 iFrame = 0; /* Wal frame containing data for iDbpage */
u32 mxSafeFrame; /* Max frame that can be backfilled */
u32 mxPage; /* Max database page to write */
int i; /* Loop counter */
volatile WalCkptInfo *pInfo; /* The checkpoint status information */
szPage = walPagesize(pWal);
testcase( szPage<=32768 );
testcase( szPage>=65536 );
pInfo = walCkptInfo(pWal);
if( pInfo->nBackfill<pWal->hdr.mxFrame ){
/* Allocate the iterator */
rc = walIteratorInit(pWal, &pIter);
if( rc!=SQLITE_OK ){
return rc;
}
assert( pIter );
/* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked
** in the SQLITE_CHECKPOINT_PASSIVE mode. */
assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 );
/* Compute in mxSafeFrame the index of the last frame of the WAL that is
** safe to write into the database. Frames beyond mxSafeFrame might
** overwrite database pages that are in use by active readers and thus
** cannot be backfilled from the WAL.
*/
mxSafeFrame = pWal->hdr.mxFrame;
mxPage = pWal->hdr.nPage;
for(i=1; i<WAL_NREADER; i++){
/* Thread-sanitizer reports that the following is an unsafe read,
** as some other thread may be in the process of updating the value
** of the aReadMark[] slot. The assumption here is that if that is
** happening, the other client may only be increasing the value,
** not decreasing it. So assuming either that either the "old" or
** "new" version of the value is read, and not some arbitrary value
** that would never be written by a real client, things are still
** safe. */
u32 y = pInfo->aReadMark[i];
if( mxSafeFrame>y ){
assert( y<=pWal->hdr.mxFrame );
rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(i), 1);
if( rc==SQLITE_OK ){
pInfo->aReadMark[i] = (i==1 ? mxSafeFrame : READMARK_NOT_USED);
walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
}else if( rc==SQLITE_BUSY ){
mxSafeFrame = y;
xBusy = 0;
}else{
goto walcheckpoint_out;
}
}
}
if( pInfo->nBackfill<mxSafeFrame
&& (rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(0),1))==SQLITE_OK
){
i64 nSize; /* Current size of database file */
u32 nBackfill = pInfo->nBackfill;
pInfo->nBackfillAttempted = mxSafeFrame;
/* Sync the WAL to disk */
rc = sqlite3OsSync(pWal->pWalFd, CKPT_SYNC_FLAGS(sync_flags));
/* If the database may grow as a result of this checkpoint, hint
** about the eventual size of the db file to the VFS layer.
*/
if( rc==SQLITE_OK ){
i64 nReq = ((i64)mxPage * szPage);
rc = sqlite3OsFileSize(pWal->pDbFd, &nSize);
if( rc==SQLITE_OK && nSize<nReq ){
sqlite3OsFileControlHint(pWal->pDbFd, SQLITE_FCNTL_SIZE_HINT, &nReq);
}
}
/* Iterate through the contents of the WAL, copying data to the db file */
while( rc==SQLITE_OK && 0==walIteratorNext(pIter, &iDbpage, &iFrame) ){
i64 iOffset;
assert( walFramePgno(pWal, iFrame)==iDbpage );
if( db->u1.isInterrupted ){
rc = db->mallocFailed ? SQLITE_NOMEM_BKPT : SQLITE_INTERRUPT;
break;
}
if( iFrame<=nBackfill || iFrame>mxSafeFrame || iDbpage>mxPage ){
continue;
}
iOffset = walFrameOffset(iFrame, szPage) + WAL_FRAME_HDRSIZE;
/* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL file */
rc = sqlite3OsRead(pWal->pWalFd, zBuf, szPage, iOffset);
if( rc!=SQLITE_OK ) break;
iOffset = (iDbpage-1)*(i64)szPage;
testcase( IS_BIG_INT(iOffset) );
rc = sqlite3OsWrite(pWal->pDbFd, zBuf, szPage, iOffset);
if( rc!=SQLITE_OK ) break;
}
/* If work was actually accomplished... */
if( rc==SQLITE_OK ){
if( mxSafeFrame==walIndexHdr(pWal)->mxFrame ){
i64 szDb = pWal->hdr.nPage*(i64)szPage;
testcase( IS_BIG_INT(szDb) );
rc = sqlite3OsTruncate(pWal->pDbFd, szDb);
if( rc==SQLITE_OK ){
rc = sqlite3OsSync(pWal->pDbFd, CKPT_SYNC_FLAGS(sync_flags));
}
}
if( rc==SQLITE_OK ){
pInfo->nBackfill = mxSafeFrame;
}
}
/* Release the reader lock held while backfilling */
walUnlockExclusive(pWal, WAL_READ_LOCK(0), 1);
}
if( rc==SQLITE_BUSY ){
/* Reset the return code so as not to report a checkpoint failure
** just because there are active readers. */
rc = SQLITE_OK;
}
}
/* If this is an SQLITE_CHECKPOINT_RESTART or TRUNCATE operation, and the
** entire wal file has been copied into the database file, then block
** until all readers have finished using the wal file. This ensures that
** the next process to write to the database restarts the wal file.
*/
if( rc==SQLITE_OK && eMode!=SQLITE_CHECKPOINT_PASSIVE ){
assert( pWal->writeLock );
if( pInfo->nBackfill<pWal->hdr.mxFrame ){
rc = SQLITE_BUSY;
}else if( eMode>=SQLITE_CHECKPOINT_RESTART ){
u32 salt1;
sqlite3_randomness(4, &salt1);
assert( pInfo->nBackfill==pWal->hdr.mxFrame );
rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(1), WAL_NREADER-1);
if( rc==SQLITE_OK ){
if( eMode==SQLITE_CHECKPOINT_TRUNCATE ){
/* IMPLEMENTATION-OF: R-44699-57140 This mode works the same way as
** SQLITE_CHECKPOINT_RESTART with the addition that it also
** truncates the log file to zero bytes just prior to a
** successful return.
**
** In theory, it might be safe to do this without updating the
** wal-index header in shared memory, as all subsequent reader or
** writer clients should see that the entire log file has been
** checkpointed and behave accordingly. This seems unsafe though,
** as it would leave the system in a state where the contents of
** the wal-index header do not match the contents of the
** file-system. To avoid this, update the wal-index header to
** indicate that the log file contains zero valid frames. */
walRestartHdr(pWal, salt1);
rc = sqlite3OsTruncate(pWal->pWalFd, 0);
}
walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
}
}
}
walcheckpoint_out:
walIteratorFree(pIter);
return rc;
}
/*
** If the WAL file is currently larger than nMax bytes in size, truncate
** it to exactly nMax bytes. If an error occurs while doing so, ignore it.
*/
static void walLimitSize(Wal *pWal, i64 nMax){
i64 sz;
int rx;
sqlite3BeginBenignMalloc();
rx = sqlite3OsFileSize(pWal->pWalFd, &sz);
if( rx==SQLITE_OK && (sz > nMax ) ){
rx = sqlite3OsTruncate(pWal->pWalFd, nMax);
}
sqlite3EndBenignMalloc();
if( rx ){
sqlite3_log(rx, "cannot limit WAL size: %s", pWal->zWalName);
}
}
/*
** Close a connection to a log file.
*/
int sqlite3WalClose(
Wal *pWal, /* Wal to close */
sqlite3 *db, /* For interrupt flag */
int sync_flags, /* Flags to pass to OsSync() (or 0) */
int nBuf,
u8 *zBuf /* Buffer of at least nBuf bytes */
){
int rc = SQLITE_OK;
if( pWal ){
int isDelete = 0; /* True to unlink wal and wal-index files */
/* If an EXCLUSIVE lock can be obtained on the database file (using the
** ordinary, rollback-mode locking methods, this guarantees that the
** connection associated with this log file is the only connection to
** the database. In this case checkpoint the database and unlink both
** the wal and wal-index files.
**
** The EXCLUSIVE lock is not released before returning.
*/
if( zBuf!=0
&& SQLITE_OK==(rc = sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE))
){
if( pWal->exclusiveMode==WAL_NORMAL_MODE ){
pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
}
rc = sqlite3WalCheckpoint(pWal, db,
SQLITE_CHECKPOINT_PASSIVE, 0, 0, sync_flags, nBuf, zBuf, 0, 0
);
if( rc==SQLITE_OK ){
int bPersist = -1;
sqlite3OsFileControlHint(
pWal->pDbFd, SQLITE_FCNTL_PERSIST_WAL, &bPersist
);
if( bPersist!=1 ){
/* Try to delete the WAL file if the checkpoint completed and
** fsyned (rc==SQLITE_OK) and if we are not in persistent-wal
** mode (!bPersist) */
isDelete = 1;
}else if( pWal->mxWalSize>=0 ){
/* Try to truncate the WAL file to zero bytes if the checkpoint
** completed and fsynced (rc==SQLITE_OK) and we are in persistent
** WAL mode (bPersist) and if the PRAGMA journal_size_limit is a
** non-negative value (pWal->mxWalSize>=0). Note that we truncate
** to zero bytes as truncating to the journal_size_limit might
** leave a corrupt WAL file on disk. */
walLimitSize(pWal, 0);
}
}
}
walIndexClose(pWal, isDelete);
sqlite3OsClose(pWal->pWalFd);
if( isDelete ){
sqlite3BeginBenignMalloc();
sqlite3OsDelete(pWal->pVfs, pWal->zWalName, 0);
sqlite3EndBenignMalloc();
}
WALTRACE(("WAL%p: closed\n", pWal));
sqlite3_free((void *)pWal->apWiData);
sqlite3_free(pWal);
}
return rc;
}
/*
** Try to read the wal-index header. Return 0 on success and 1 if
** there is a problem.
**
** The wal-index is in shared memory. Another thread or process might
** be writing the header at the same time this procedure is trying to
** read it, which might result in inconsistency. A dirty read is detected
** by verifying that both copies of the header are the same and also by
** a checksum on the header.
**
** If and only if the read is consistent and the header is different from
** pWal->hdr, then pWal->hdr is updated to the content of the new header
** and *pChanged is set to 1.
**
** If the checksum cannot be verified return non-zero. If the header
** is read successfully and the checksum verified, return zero.
*/
static int walIndexTryHdr(Wal *pWal, int *pChanged){
u32 aCksum[2]; /* Checksum on the header content */
WalIndexHdr h1, h2; /* Two copies of the header content */
WalIndexHdr volatile *aHdr; /* Header in shared memory */
/* The first page of the wal-index must be mapped at this point. */
assert( pWal->nWiData>0 && pWal->apWiData[0] );
/* Read the header. This might happen concurrently with a write to the
** same area of shared memory on a different CPU in a SMP,
** meaning it is possible that an inconsistent snapshot is read
** from the file. If this happens, return non-zero.
**
** There are two copies of the header at the beginning of the wal-index.
** When reading, read [0] first then [1]. Writes are in the reverse order.
** Memory barriers are used to prevent the compiler or the hardware from
** reordering the reads and writes.
*/
aHdr = walIndexHdr(pWal);
memcpy(&h1, (void *)&aHdr[0], sizeof(h1));
walShmBarrier(pWal);
memcpy(&h2, (void *)&aHdr[1], sizeof(h2));
if( memcmp(&h1, &h2, sizeof(h1))!=0 ){
return 1; /* Dirty read */
}
if( h1.isInit==0 ){
return 1; /* Malformed header - probably all zeros */
}
walChecksumBytes(1, (u8*)&h1, sizeof(h1)-sizeof(h1.aCksum), 0, aCksum);
if( aCksum[0]!=h1.aCksum[0] || aCksum[1]!=h1.aCksum[1] ){
return 1; /* Checksum does not match */
}
if( memcmp(&pWal->hdr, &h1, sizeof(WalIndexHdr)) ){
*pChanged = 1;
memcpy(&pWal->hdr, &h1, sizeof(WalIndexHdr));
pWal->szPage = (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16);
testcase( pWal->szPage<=32768 );
testcase( pWal->szPage>=65536 );
}
/* The header was successfully read. Return zero. */
return 0;
}
/*
** This is the value that walTryBeginRead returns when it needs to
** be retried.
*/
#define WAL_RETRY (-1)
/*
** Read the wal-index header from the wal-index and into pWal->hdr.
** If the wal-header appears to be corrupt, try to reconstruct the
** wal-index from the WAL before returning.
**
** Set *pChanged to 1 if the wal-index header value in pWal->hdr is
** changed by this operation. If pWal->hdr is unchanged, set *pChanged
** to 0.
**
** If the wal-index header is successfully read, return SQLITE_OK.
** Otherwise an SQLite error code.
*/
static int walIndexReadHdr(Wal *pWal, int *pChanged){
int rc; /* Return code */
int badHdr; /* True if a header read failed */
volatile u32 *page0; /* Chunk of wal-index containing header */
/* Ensure that page 0 of the wal-index (the page that contains the
** wal-index header) is mapped. Return early if an error occurs here.
*/
assert( pChanged );
rc = walIndexPage(pWal, 0, &page0);
if( rc!=SQLITE_OK ){
assert( rc!=SQLITE_READONLY ); /* READONLY changed to OK in walIndexPage */
if( rc==SQLITE_READONLY_CANTINIT ){
/* The SQLITE_READONLY_CANTINIT return means that the shared-memory
** was openable but is not writable, and this thread is unable to
** confirm that another write-capable connection has the shared-memory
** open, and hence the content of the shared-memory is unreliable,
** since the shared-memory might be inconsistent with the WAL file
** and there is no writer on hand to fix it. */
assert( page0==0 );
assert( pWal->writeLock==0 );
assert( pWal->readOnly & WAL_SHM_RDONLY );
pWal->bShmUnreliable = 1;
pWal->exclusiveMode = WAL_HEAPMEMORY_MODE;
*pChanged = 1;
}else{
return rc; /* Any other non-OK return is just an error */
}
}else{
/* page0 can be NULL if the SHM is zero bytes in size and pWal->writeLock
** is zero, which prevents the SHM from growing */
testcase( page0!=0 );
}
assert( page0!=0 || pWal->writeLock==0 );
/* If the first page of the wal-index has been mapped, try to read the
** wal-index header immediately, without holding any lock. This usually
** works, but may fail if the wal-index header is corrupt or currently
** being modified by another thread or process.
*/
badHdr = (page0 ? walIndexTryHdr(pWal, pChanged) : 1);
/* If the first attempt failed, it might have been due to a race
** with a writer. So get a WRITE lock and try again.
*/
assert( badHdr==0 || pWal->writeLock==0 );
if( badHdr ){
if( pWal->bShmUnreliable==0 && (pWal->readOnly & WAL_SHM_RDONLY) ){
if( SQLITE_OK==(rc = walLockShared(pWal, WAL_WRITE_LOCK)) ){
walUnlockShared(pWal, WAL_WRITE_LOCK);
rc = SQLITE_READONLY_RECOVERY;
}
}else if( SQLITE_OK==(rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1)) ){
pWal->writeLock = 1;
if( SQLITE_OK==(rc = walIndexPage(pWal, 0, &page0)) ){
badHdr = walIndexTryHdr(pWal, pChanged);
if( badHdr ){
/* If the wal-index header is still malformed even while holding
** a WRITE lock, it can only mean that the header is corrupted and
** needs to be reconstructed. So run recovery to do exactly that.
*/
rc = walIndexRecover(pWal);
*pChanged = 1;
}
}
pWal->writeLock = 0;
walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
}
}
/* If the header is read successfully, check the version number to make
** sure the wal-index was not constructed with some future format that
** this version of SQLite cannot understand.
*/
if( badHdr==0 && pWal->hdr.iVersion!=WALINDEX_MAX_VERSION ){
rc = SQLITE_CANTOPEN_BKPT;
}
if( pWal->bShmUnreliable ){
if( rc!=SQLITE_OK ){
walIndexClose(pWal, 0);
pWal->bShmUnreliable = 0;
assert( pWal->nWiData>0 && pWal->apWiData[0]==0 );
/* walIndexRecover() might have returned SHORT_READ if a concurrent
** writer truncated the WAL out from under it. If that happens, it
** indicates that a writer has fixed the SHM file for us, so retry */
if( rc==SQLITE_IOERR_SHORT_READ ) rc = WAL_RETRY;
}
pWal->exclusiveMode = WAL_NORMAL_MODE;
}
return rc;
}
/*
** Open a transaction in a connection where the shared-memory is read-only
** and where we cannot verify that there is a separate write-capable connection
** on hand to keep the shared-memory up-to-date with the WAL file.
**
** This can happen, for example, when the shared-memory is implemented by
** memory-mapping a *-shm file, where a prior writer has shut down and
** left the *-shm file on disk, and now the present connection is trying
** to use that database but lacks write permission on the *-shm file.
** Other scenarios are also possible, depending on the VFS implementation.
**
** Precondition:
**
** The *-wal file has been read and an appropriate wal-index has been
** constructed in pWal->apWiData[] using heap memory instead of shared
** memory.
**
** If this function returns SQLITE_OK, then the read transaction has
** been successfully opened. In this case output variable (*pChanged)
** is set to true before returning if the caller should discard the
** contents of the page cache before proceeding. Or, if it returns
** WAL_RETRY, then the heap memory wal-index has been discarded and
** the caller should retry opening the read transaction from the
** beginning (including attempting to map the *-shm file).
**
** If an error occurs, an SQLite error code is returned.
*/
static int walBeginShmUnreliable(Wal *pWal, int *pChanged){
i64 szWal; /* Size of wal file on disk in bytes */
i64 iOffset; /* Current offset when reading wal file */
u8 aBuf[WAL_HDRSIZE]; /* Buffer to load WAL header into */
u8 *aFrame = 0; /* Malloc'd buffer to load entire frame */
int szFrame; /* Number of bytes in buffer aFrame[] */
u8 *aData; /* Pointer to data part of aFrame buffer */
volatile void *pDummy; /* Dummy argument for xShmMap */
int rc; /* Return code */
u32 aSaveCksum[2]; /* Saved copy of pWal->hdr.aFrameCksum */
assert( pWal->bShmUnreliable );
assert( pWal->readOnly & WAL_SHM_RDONLY );
assert( pWal->nWiData>0 && pWal->apWiData[0] );
/* Take WAL_READ_LOCK(0). This has the effect of preventing any
** writers from running a checkpoint, but does not stop them
** from running recovery. */
rc = walLockShared(pWal, WAL_READ_LOCK(0));
if( rc!=SQLITE_OK ){
if( rc==SQLITE_BUSY ) rc = WAL_RETRY;
goto begin_unreliable_shm_out;
}
pWal->readLock = 0;
/* Check to see if a separate writer has attached to the shared-memory area,
** thus making the shared-memory "reliable" again. Do this by invoking
** the xShmMap() routine of the VFS and looking to see if the return
** is SQLITE_READONLY instead of SQLITE_READONLY_CANTINIT.
**
** If the shared-memory is now "reliable" return WAL_RETRY, which will
** cause the heap-memory WAL-index to be discarded and the actual
** shared memory to be used in its place.
**
** This step is important because, even though this connection is holding
** the WAL_READ_LOCK(0) which prevents a checkpoint, a writer might
** have already checkpointed the WAL file and, while the current
** is active, wrap the WAL and start overwriting frames that this
** process wants to use.
**
** Once sqlite3OsShmMap() has been called for an sqlite3_file and has
** returned any SQLITE_READONLY value, it must return only SQLITE_READONLY
** or SQLITE_READONLY_CANTINIT or some error for all subsequent invocations,
** even if some external agent does a "chmod" to make the shared-memory
** writable by us, until sqlite3OsShmUnmap() has been called.
** This is a requirement on the VFS implementation.
*/
rc = sqlite3OsShmMap(pWal->pDbFd, 0, WALINDEX_PGSZ, 0, &pDummy);
assert( rc!=SQLITE_OK ); /* SQLITE_OK not possible for read-only connection */
if( rc!=SQLITE_READONLY_CANTINIT ){
rc = (rc==SQLITE_READONLY ? WAL_RETRY : rc);
goto begin_unreliable_shm_out;
}
/* We reach this point only if the real shared-memory is still unreliable.
** Assume the in-memory WAL-index substitute is correct and load it
** into pWal->hdr.
*/
memcpy(&pWal->hdr, (void*)walIndexHdr(pWal), sizeof(WalIndexHdr));
/* Make sure some writer hasn't come in and changed the WAL file out
** from under us, then disconnected, while we were not looking.
*/
rc = sqlite3OsFileSize(pWal->pWalFd, &szWal);
if( rc!=SQLITE_OK ){
goto begin_unreliable_shm_out;
}
if( szWal<WAL_HDRSIZE ){
/* If the wal file is too small to contain a wal-header and the
** wal-index header has mxFrame==0, then it must be safe to proceed
** reading the database file only. However, the page cache cannot
** be trusted, as a read/write connection may have connected, written
** the db, run a checkpoint, truncated the wal file and disconnected
** since this client's last read transaction. */
*pChanged = 1;
rc = (pWal->hdr.mxFrame==0 ? SQLITE_OK : WAL_RETRY);
goto begin_unreliable_shm_out;
}
/* Check the salt keys at the start of the wal file still match. */
rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0);
if( rc!=SQLITE_OK ){
goto begin_unreliable_shm_out;
}
if( memcmp(&pWal->hdr.aSalt, &aBuf[16], 8) ){
/* Some writer has wrapped the WAL file while we were not looking.
** Return WAL_RETRY which will cause the in-memory WAL-index to be
** rebuilt. */
rc = WAL_RETRY;
goto begin_unreliable_shm_out;
}
/* Allocate a buffer to read frames into */
szFrame = pWal->hdr.szPage + WAL_FRAME_HDRSIZE;
aFrame = (u8 *)sqlite3_malloc64(szFrame);
if( aFrame==0 ){
rc = SQLITE_NOMEM_BKPT;
goto begin_unreliable_shm_out;
}
aData = &aFrame[WAL_FRAME_HDRSIZE];
/* Check to see if a complete transaction has been appended to the
** wal file since the heap-memory wal-index was created. If so, the
** heap-memory wal-index is discarded and WAL_RETRY returned to
** the caller. */
aSaveCksum[0] = pWal->hdr.aFrameCksum[0];
aSaveCksum[1] = pWal->hdr.aFrameCksum[1];
for(iOffset=walFrameOffset(pWal->hdr.mxFrame+1, pWal->hdr.szPage);
iOffset+szFrame<=szWal;
iOffset+=szFrame
){
u32 pgno; /* Database page number for frame */
u32 nTruncate; /* dbsize field from frame header */
/* Read and decode the next log frame. */
rc = sqlite3OsRead(pWal->pWalFd, aFrame, szFrame, iOffset);
if( rc!=SQLITE_OK ) break;
if( !walDecodeFrame(pWal, &pgno, &nTruncate, aData, aFrame) ) break;
/* If nTruncate is non-zero, then a complete transaction has been
** appended to this wal file. Set rc to WAL_RETRY and break out of
** the loop. */
if( nTruncate ){
rc = WAL_RETRY;
break;
}
}
pWal->hdr.aFrameCksum[0] = aSaveCksum[0];
pWal->hdr.aFrameCksum[1] = aSaveCksum[1];
begin_unreliable_shm_out:
sqlite3_free(aFrame);
if( rc!=SQLITE_OK ){
int i;
for(i=0; i<pWal->nWiData; i++){
sqlite3_free((void*)pWal->apWiData[i]);
pWal->apWiData[i] = 0;
}
pWal->bShmUnreliable = 0;
sqlite3WalEndReadTransaction(pWal);
*pChanged = 1;
}
return rc;
}
/*
** Attempt to start a read transaction. This might fail due to a race or
** other transient condition. When that happens, it returns WAL_RETRY to
** indicate to the caller that it is safe to retry immediately.
**
** On success return SQLITE_OK. On a permanent failure (such an
** I/O error or an SQLITE_BUSY because another process is running
** recovery) return a positive error code.
**
** The useWal parameter is true to force the use of the WAL and disable
** the case where the WAL is bypassed because it has been completely
** checkpointed. If useWal==0 then this routine calls walIndexReadHdr()
** to make a copy of the wal-index header into pWal->hdr. If the
** wal-index header has changed, *pChanged is set to 1 (as an indication
** to the caller that the local page cache is obsolete and needs to be
** flushed.) When useWal==1, the wal-index header is assumed to already
** be loaded and the pChanged parameter is unused.
**
** The caller must set the cnt parameter to the number of prior calls to
** this routine during the current read attempt that returned WAL_RETRY.
** This routine will start taking more aggressive measures to clear the
** race conditions after multiple WAL_RETRY returns, and after an excessive
** number of errors will ultimately return SQLITE_PROTOCOL. The
** SQLITE_PROTOCOL return indicates that some other process has gone rogue
** and is not honoring the locking protocol. There is a vanishingly small
** chance that SQLITE_PROTOCOL could be returned because of a run of really
** bad luck when there is lots of contention for the wal-index, but that
** possibility is so small that it can be safely neglected, we believe.
**
** On success, this routine obtains a read lock on
** WAL_READ_LOCK(pWal->readLock). The pWal->readLock integer is
** in the range 0 <= pWal->readLock < WAL_NREADER. If pWal->readLock==(-1)
** that means the Wal does not hold any read lock. The reader must not
** access any database page that is modified by a WAL frame up to and
** including frame number aReadMark[pWal->readLock]. The reader will
** use WAL frames up to and including pWal->hdr.mxFrame if pWal->readLock>0
** Or if pWal->readLock==0, then the reader will ignore the WAL
** completely and get all content directly from the database file.
** If the useWal parameter is 1 then the WAL will never be ignored and
** this routine will always set pWal->readLock>0 on success.
** When the read transaction is completed, the caller must release the
** lock on WAL_READ_LOCK(pWal->readLock) and set pWal->readLock to -1.
**
** This routine uses the nBackfill and aReadMark[] fields of the header
** to select a particular WAL_READ_LOCK() that strives to let the
** checkpoint process do as much work as possible. This routine might
** update values of the aReadMark[] array in the header, but if it does
** so it takes care to hold an exclusive lock on the corresponding
** WAL_READ_LOCK() while changing values.
*/
static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
volatile WalCkptInfo *pInfo; /* Checkpoint information in wal-index */
u32 mxReadMark; /* Largest aReadMark[] value */
int mxI; /* Index of largest aReadMark[] value */
int i; /* Loop counter */
int rc = SQLITE_OK; /* Return code */
u32 mxFrame; /* Wal frame to lock to */
assert( pWal->readLock<0 ); /* Not currently locked */
/* useWal may only be set for read/write connections */
assert( (pWal->readOnly & WAL_SHM_RDONLY)==0 || useWal==0 );
/* Take steps to avoid spinning forever if there is a protocol error.
**
** Circumstances that cause a RETRY should only last for the briefest
** instances of time. No I/O or other system calls are done while the
** locks are held, so the locks should not be held for very long. But
** if we are unlucky, another process that is holding a lock might get
** paged out or take a page-fault that is time-consuming to resolve,
** during the few nanoseconds that it is holding the lock. In that case,
** it might take longer than normal for the lock to free.
**
** After 5 RETRYs, we begin calling sqlite3OsSleep(). The first few
** calls to sqlite3OsSleep() have a delay of 1 microsecond. Really this
** is more of a scheduler yield than an actual delay. But on the 10th
** an subsequent retries, the delays start becoming longer and longer,
** so that on the 100th (and last) RETRY we delay for 323 milliseconds.
** The total delay time before giving up is less than 10 seconds.
*/
if( cnt>5 ){
int nDelay = 1; /* Pause time in microseconds */
if( cnt>100 ){
VVA_ONLY( pWal->lockError = 1; )
return SQLITE_PROTOCOL;
}
if( cnt>=10 ) nDelay = (cnt-9)*(cnt-9)*39;
sqlite3OsSleep(pWal->pVfs, nDelay);
}
if( !useWal ){
assert( rc==SQLITE_OK );
if( pWal->bShmUnreliable==0 ){
rc = walIndexReadHdr(pWal, pChanged);
}
if( rc==SQLITE_BUSY ){
/* If there is not a recovery running in another thread or process
** then convert BUSY errors to WAL_RETRY. If recovery is known to
** be running, convert BUSY to BUSY_RECOVERY. There is a race here
** which might cause WAL_RETRY to be returned even if BUSY_RECOVERY
** would be technically correct. But the race is benign since with
** WAL_RETRY this routine will be called again and will probably be
** right on the second iteration.
*/
if( pWal->apWiData[0]==0 ){
/* This branch is taken when the xShmMap() method returns SQLITE_BUSY.
** We assume this is a transient condition, so return WAL_RETRY. The
** xShmMap() implementation used by the default unix and win32 VFS
** modules may return SQLITE_BUSY due to a race condition in the
** code that determines whether or not the shared-memory region
** must be zeroed before the requested page is returned.
*/
rc = WAL_RETRY;
}else if( SQLITE_OK==(rc = walLockShared(pWal, WAL_RECOVER_LOCK)) ){
walUnlockShared(pWal, WAL_RECOVER_LOCK);
rc = WAL_RETRY;
}else if( rc==SQLITE_BUSY ){
rc = SQLITE_BUSY_RECOVERY;
}
}
if( rc!=SQLITE_OK ){
return rc;
}
else if( pWal->bShmUnreliable ){
return walBeginShmUnreliable(pWal, pChanged);
}
}
assert( pWal->nWiData>0 );
assert( pWal->apWiData[0]!=0 );
pInfo = walCkptInfo(pWal);
if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame
#ifdef SQLITE_ENABLE_SNAPSHOT
&& (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0)
#endif
){
/* The WAL has been completely backfilled (or it is empty).
** and can be safely ignored.
*/
rc = walLockShared(pWal, WAL_READ_LOCK(0));
walShmBarrier(pWal);
if( rc==SQLITE_OK ){
if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){
/* It is not safe to allow the reader to continue here if frames
** may have been appended to the log before READ_LOCK(0) was obtained.
** When holding READ_LOCK(0), the reader ignores the entire log file,
** which implies that the database file contains a trustworthy
** snapshot. Since holding READ_LOCK(0) prevents a checkpoint from
** happening, this is usually correct.
**
** However, if frames have been appended to the log (or if the log
** is wrapped and written for that matter) before the READ_LOCK(0)
** is obtained, that is not necessarily true. A checkpointer may
** have started to backfill the appended frames but crashed before
** it finished. Leaving a corrupt image in the database file.
*/
walUnlockShared(pWal, WAL_READ_LOCK(0));
return WAL_RETRY;
}
pWal->readLock = 0;
return SQLITE_OK;
}else if( rc!=SQLITE_BUSY ){
return rc;
}
}
/* If we get this far, it means that the reader will want to use
** the WAL to get at content from recent commits. The job now is
** to select one of the aReadMark[] entries that is closest to
** but not exceeding pWal->hdr.mxFrame and lock that entry.
*/
mxReadMark = 0;
mxI = 0;
mxFrame = pWal->hdr.mxFrame;
#ifdef SQLITE_ENABLE_SNAPSHOT
if( pWal->pSnapshot && pWal->pSnapshot->mxFrame<mxFrame ){
mxFrame = pWal->pSnapshot->mxFrame;
}
#endif
for(i=1; i<WAL_NREADER; i++){
u32 thisMark = pInfo->aReadMark[i];
if( mxReadMark<=thisMark && thisMark<=mxFrame ){
assert( thisMark!=READMARK_NOT_USED );
mxReadMark = thisMark;
mxI = i;
}
}
if( (pWal->readOnly & WAL_SHM_RDONLY)==0
&& (mxReadMark<mxFrame || mxI==0)
){
for(i=1; i<WAL_NREADER; i++){
rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
if( rc==SQLITE_OK ){
mxReadMark = pInfo->aReadMark[i] = mxFrame;
mxI = i;
walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
break;
}else if( rc!=SQLITE_BUSY ){
return rc;
}
}
}
if( mxI==0 ){
assert( rc==SQLITE_BUSY || (pWal->readOnly & WAL_SHM_RDONLY)!=0 );
return rc==SQLITE_BUSY ? WAL_RETRY : SQLITE_READONLY_CANTINIT;
}
rc = walLockShared(pWal, WAL_READ_LOCK(mxI));
if( rc ){
return rc==SQLITE_BUSY ? WAL_RETRY : rc;
}
/* Now that the read-lock has been obtained, check that neither the
** value in the aReadMark[] array or the contents of the wal-index
** header have changed.
**
** It is necessary to check that the wal-index header did not change
** between the time it was read and when the shared-lock was obtained
** on WAL_READ_LOCK(mxI) was obtained to account for the possibility
** that the log file may have been wrapped by a writer, or that frames
** that occur later in the log than pWal->hdr.mxFrame may have been
** copied into the database by a checkpointer. If either of these things
** happened, then reading the database with the current value of
** pWal->hdr.mxFrame risks reading a corrupted snapshot. So, retry
** instead.
**
** Before checking that the live wal-index header has not changed
** since it was read, set Wal.minFrame to the first frame in the wal
** file that has not yet been checkpointed. This client will not need
** to read any frames earlier than minFrame from the wal file - they
** can be safely read directly from the database file.
**
** Because a ShmBarrier() call is made between taking the copy of
** nBackfill and checking that the wal-header in shared-memory still
** matches the one cached in pWal->hdr, it is guaranteed that the
** checkpointer that set nBackfill was not working with a wal-index
** header newer than that cached in pWal->hdr. If it were, that could
** cause a problem. The checkpointer could omit to checkpoint
** a version of page X that lies before pWal->minFrame (call that version
** A) on the basis that there is a newer version (version B) of the same
** page later in the wal file. But if version B happens to like past
** frame pWal->hdr.mxFrame - then the client would incorrectly assume
** that it can read version A from the database file. However, since
** we can guarantee that the checkpointer that set nBackfill could not
** see any pages past pWal->hdr.mxFrame, this problem does not come up.
*/
pWal->minFrame = pInfo->nBackfill+1;
walShmBarrier(pWal);
if( pInfo->aReadMark[mxI]!=mxReadMark
|| memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr))
){
walUnlockShared(pWal, WAL_READ_LOCK(mxI));
return WAL_RETRY;
}else{
assert( mxReadMark<=pWal->hdr.mxFrame );
pWal->readLock = (i16)mxI;
}
return rc;
}
#ifdef SQLITE_ENABLE_SNAPSHOT
/*
** Attempt to reduce the value of the WalCkptInfo.nBackfillAttempted
** variable so that older snapshots can be accessed. To do this, loop
** through all wal frames from nBackfillAttempted to (nBackfill+1),
** comparing their content to the corresponding page with the database
** file, if any. Set nBackfillAttempted to the frame number of the
** first frame for which the wal file content matches the db file.
**
** This is only really safe if the file-system is such that any page
** writes made by earlier checkpointers were atomic operations, which
** is not always true. It is also possible that nBackfillAttempted
** may be left set to a value larger than expected, if a wal frame
** contains content that duplicate of an earlier version of the same
** page.
**
** SQLITE_OK is returned if successful, or an SQLite error code if an
** error occurs. It is not an error if nBackfillAttempted cannot be
** decreased at all.
*/
int sqlite3WalSnapshotRecover(Wal *pWal){
int rc;
assert( pWal->readLock>=0 );
rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
if( rc==SQLITE_OK ){
volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
int szPage = (int)pWal->szPage;
i64 szDb; /* Size of db file in bytes */
rc = sqlite3OsFileSize(pWal->pDbFd, &szDb);
if( rc==SQLITE_OK ){
void *pBuf1 = sqlite3_malloc(szPage);
void *pBuf2 = sqlite3_malloc(szPage);
if( pBuf1==0 || pBuf2==0 ){
rc = SQLITE_NOMEM;
}else{
u32 i = pInfo->nBackfillAttempted;
for(i=pInfo->nBackfillAttempted; i>pInfo->nBackfill; i--){
volatile ht_slot *dummy;
volatile u32 *aPgno; /* Array of page numbers */
u32 iZero; /* Frame corresponding to aPgno[0] */
u32 pgno; /* Page number in db file */
i64 iDbOff; /* Offset of db file entry */
i64 iWalOff; /* Offset of wal file entry */
rc = walHashGet(pWal, walFramePage(i), &dummy, &aPgno, &iZero);
if( rc!=SQLITE_OK ) break;
pgno = aPgno[i-iZero];
iDbOff = (i64)(pgno-1) * szPage;
if( iDbOff+szPage<=szDb ){
iWalOff = walFrameOffset(i, szPage) + WAL_FRAME_HDRSIZE;
rc = sqlite3OsRead(pWal->pWalFd, pBuf1, szPage, iWalOff);
if( rc==SQLITE_OK ){
rc = sqlite3OsRead(pWal->pDbFd, pBuf2, szPage, iDbOff);
}
if( rc!=SQLITE_OK || 0==memcmp(pBuf1, pBuf2, szPage) ){
break;
}
}
pInfo->nBackfillAttempted = i-1;
}
}
sqlite3_free(pBuf1);
sqlite3_free(pBuf2);
}
walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
}
return rc;
}
#endif /* SQLITE_ENABLE_SNAPSHOT */
/*
** Begin a read transaction on the database.
**
** This routine used to be called sqlite3OpenSnapshot() and with good reason:
** it takes a snapshot of the state of the WAL and wal-index for the current
** instant in time. The current thread will continue to use this snapshot.
** Other threads might append new content to the WAL and wal-index but
** that extra content is ignored by the current thread.
**
** If the database contents have changes since the previous read
** transaction, then *pChanged is set to 1 before returning. The
** Pager layer will use this to know that is cache is stale and
** needs to be flushed.
*/
int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
int rc; /* Return code */
int cnt = 0; /* Number of TryBeginRead attempts */
#ifdef SQLITE_ENABLE_SNAPSHOT
int bChanged = 0;
WalIndexHdr *pSnapshot = pWal->pSnapshot;
if( pSnapshot && memcmp(pSnapshot, &pWal->hdr, sizeof(WalIndexHdr))!=0 ){
bChanged = 1;
}
#endif
do{
rc = walTryBeginRead(pWal, pChanged, 0, ++cnt);
}while( rc==WAL_RETRY );
testcase( (rc&0xff)==SQLITE_BUSY );
testcase( (rc&0xff)==SQLITE_IOERR );
testcase( rc==SQLITE_PROTOCOL );
testcase( rc==SQLITE_OK );
#ifdef SQLITE_ENABLE_SNAPSHOT
if( rc==SQLITE_OK ){
if( pSnapshot && memcmp(pSnapshot, &pWal->hdr, sizeof(WalIndexHdr))!=0 ){
/* At this point the client has a lock on an aReadMark[] slot holding
** a value equal to or smaller than pSnapshot->mxFrame, but pWal->hdr
** is populated with the wal-index header corresponding to the head
** of the wal file. Verify that pSnapshot is still valid before
** continuing. Reasons why pSnapshot might no longer be valid:
**
** (1) The WAL file has been reset since the snapshot was taken.
** In this case, the salt will have changed.
**
** (2) A checkpoint as been attempted that wrote frames past
** pSnapshot->mxFrame into the database file. Note that the
** checkpoint need not have completed for this to cause problems.
*/
volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
assert( pWal->readLock>0 || pWal->hdr.mxFrame==0 );
assert( pInfo->aReadMark[pWal->readLock]<=pSnapshot->mxFrame );
/* It is possible that there is a checkpointer thread running
** concurrent with this code. If this is the case, it may be that the
** checkpointer has already determined that it will checkpoint
** snapshot X, where X is later in the wal file than pSnapshot, but
** has not yet set the pInfo->nBackfillAttempted variable to indicate
** its intent. To avoid the race condition this leads to, ensure that
** there is no checkpointer process by taking a shared CKPT lock
** before checking pInfo->nBackfillAttempted.
**
** TODO: Does the aReadMark[] lock prevent a checkpointer from doing
** this already?
*/
rc = walLockShared(pWal, WAL_CKPT_LOCK);
if( rc==SQLITE_OK ){
/* Check that the wal file has not been wrapped. Assuming that it has
** not, also check that no checkpointer has attempted to checkpoint any
** frames beyond pSnapshot->mxFrame. If either of these conditions are
** true, return SQLITE_BUSY_SNAPSHOT. Otherwise, overwrite pWal->hdr
** with *pSnapshot and set *pChanged as appropriate for opening the
** snapshot. */
if( !memcmp(pSnapshot->aSalt, pWal->hdr.aSalt, sizeof(pWal->hdr.aSalt))
&& pSnapshot->mxFrame>=pInfo->nBackfillAttempted
){
assert( pWal->readLock>0 );
memcpy(&pWal->hdr, pSnapshot, sizeof(WalIndexHdr));
*pChanged = bChanged;
}else{
rc = SQLITE_BUSY_SNAPSHOT;
}
/* Release the shared CKPT lock obtained above. */
walUnlockShared(pWal, WAL_CKPT_LOCK);
}
if( rc!=SQLITE_OK ){
sqlite3WalEndReadTransaction(pWal);
}
}
}
#endif
return rc;
}
/*
** Finish with a read transaction. All this does is release the
** read-lock.
*/
void sqlite3WalEndReadTransaction(Wal *pWal){
sqlite3WalEndWriteTransaction(pWal);
if( pWal->readLock>=0 ){
walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
pWal->readLock = -1;
}
}
/*
** Search the wal file for page pgno. If found, set *piRead to the frame that
** contains the page. Otherwise, if pgno is not in the wal file, set *piRead
** to zero.
**
** Return SQLITE_OK if successful, or an error code if an error occurs. If an
** error does occur, the final value of *piRead is undefined.
*/
int sqlite3WalFindFrame(
Wal *pWal, /* WAL handle */
Pgno pgno, /* Database page number to read data for */
u32 *piRead /* OUT: Frame number (or zero) */
){
u32 iRead = 0; /* If !=0, WAL frame to return data from */
u32 iLast = pWal->hdr.mxFrame; /* Last page in WAL for this reader */
int iHash; /* Used to loop through N hash tables */
int iMinHash;
/* This routine is only be called from within a read transaction. */
assert( pWal->readLock>=0 || pWal->lockError );
/* If the "last page" field of the wal-index header snapshot is 0, then
** no data will be read from the wal under any circumstances. Return early
** in this case as an optimization. Likewise, if pWal->readLock==0,
** then the WAL is ignored by the reader so return early, as if the
** WAL were empty.
*/
if( iLast==0 || (pWal->readLock==0 && pWal->bShmUnreliable==0) ){
*piRead = 0;
return SQLITE_OK;
}
/* Search the hash table or tables for an entry matching page number
** pgno. Each iteration of the following for() loop searches one
** hash table (each hash table indexes up to HASHTABLE_NPAGE frames).
**
** This code might run concurrently to the code in walIndexAppend()
** that adds entries to the wal-index (and possibly to this hash
** table). This means the value just read from the hash
** slot (aHash[iKey]) may have been added before or after the
** current read transaction was opened. Values added after the
** read transaction was opened may have been written incorrectly -
** i.e. these slots may contain garbage data. However, we assume
** that any slots written before the current read transaction was
** opened remain unmodified.
**
** For the reasons above, the if(...) condition featured in the inner
** loop of the following block is more stringent that would be required
** if we had exclusive access to the hash-table:
**
** (aPgno[iFrame]==pgno):
** This condition filters out normal hash-table collisions.
**
** (iFrame<=iLast):
** This condition filters out entries that were added to the hash
** table after the current read-transaction had started.
*/
iMinHash = walFramePage(pWal->minFrame);
for(iHash=walFramePage(iLast); iHash>=iMinHash && iRead==0; iHash--){
volatile ht_slot *aHash; /* Pointer to hash table */
volatile u32 *aPgno; /* Pointer to array of page numbers */
u32 iZero; /* Frame number corresponding to aPgno[0] */
int iKey; /* Hash slot index */
int nCollide; /* Number of hash collisions remaining */
int rc; /* Error code */
rc = walHashGet(pWal, iHash, &aHash, &aPgno, &iZero);
if( rc!=SQLITE_OK ){
return rc;
}
nCollide = HASHTABLE_NSLOT;
for(iKey=walHash(pgno); aHash[iKey]; iKey=walNextHash(iKey)){
u32 iFrame = aHash[iKey] + iZero;
if( iFrame<=iLast && iFrame>=pWal->minFrame && aPgno[aHash[iKey]]==pgno ){
assert( iFrame>iRead || CORRUPT_DB );
iRead = iFrame;
}
if( (nCollide--)==0 ){
return SQLITE_CORRUPT_BKPT;
}
}
}
#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
/* If expensive assert() statements are available, do a linear search
** of the wal-index file content. Make sure the results agree with the
** result obtained using the hash indexes above. */
{
u32 iRead2 = 0;
u32 iTest;
assert( pWal->bShmUnreliable || pWal->minFrame>0 );
for(iTest=iLast; iTest>=pWal->minFrame && iTest>0; iTest--){
if( walFramePgno(pWal, iTest)==pgno ){
iRead2 = iTest;
break;
}
}
assert( iRead==iRead2 );
}
#endif
*piRead = iRead;
return SQLITE_OK;
}
/*
** Read the contents of frame iRead from the wal file into buffer pOut
** (which is nOut bytes in size). Return SQLITE_OK if successful, or an
** error code otherwise.
*/
int sqlite3WalReadFrame(
Wal *pWal, /* WAL handle */
u32 iRead, /* Frame to read */
int nOut, /* Size of buffer pOut in bytes */
u8 *pOut /* Buffer to write page data to */
){
int sz;
i64 iOffset;
sz = pWal->hdr.szPage;
sz = (sz&0xfe00) + ((sz&0x0001)<<16);
testcase( sz<=32768 );
testcase( sz>=65536 );
iOffset = walFrameOffset(iRead, sz) + WAL_FRAME_HDRSIZE;
/* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL */
return sqlite3OsRead(pWal->pWalFd, pOut, (nOut>sz ? sz : nOut), iOffset);
}
/*
** Return the size of the database in pages (or zero, if unknown).
*/
Pgno sqlite3WalDbsize(Wal *pWal){
if( pWal && ALWAYS(pWal->readLock>=0) ){
return pWal->hdr.nPage;
}
return 0;
}
/*
** This function starts a write transaction on the WAL.
**
** A read transaction must have already been started by a prior call
** to sqlite3WalBeginReadTransaction().
**
** If another thread or process has written into the database since
** the read transaction was started, then it is not possible for this
** thread to write as doing so would cause a fork. So this routine
** returns SQLITE_BUSY in that case and no write transaction is started.
**
** There can only be a single writer active at a time.
*/
int sqlite3WalBeginWriteTransaction(Wal *pWal){
int rc;
/* Cannot start a write transaction without first holding a read
** transaction. */
assert( pWal->readLock>=0 );
assert( pWal->writeLock==0 && pWal->iReCksum==0 );
if( pWal->readOnly ){
return SQLITE_READONLY;
}
/* Only one writer allowed at a time. Get the write lock. Return
** SQLITE_BUSY if unable.
*/
rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1);
if( rc ){
return rc;
}
pWal->writeLock = 1;
/* If another connection has written to the database file since the
** time the read transaction on this connection was started, then
** the write is disallowed.
*/
if( memcmp(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr))!=0 ){
walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
pWal->writeLock = 0;
rc = SQLITE_BUSY_SNAPSHOT;
}
return rc;
}
/*
** End a write transaction. The commit has already been done. This
** routine merely releases the lock.
*/
int sqlite3WalEndWriteTransaction(Wal *pWal){
if( pWal->writeLock ){
walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
pWal->writeLock = 0;
pWal->iReCksum = 0;
pWal->truncateOnCommit = 0;
}
return SQLITE_OK;
}
/*
** If any data has been written (but not committed) to the log file, this
** function moves the write-pointer back to the start of the transaction.
**
** Additionally, the callback function is invoked for each frame written
** to the WAL since the start of the transaction. If the callback returns
** other than SQLITE_OK, it is not invoked again and the error code is
** returned to the caller.
**
** Otherwise, if the callback function does not return an error, this
** function returns SQLITE_OK.
*/
int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx){
int rc = SQLITE_OK;
if( ALWAYS(pWal->writeLock) ){
Pgno iMax = pWal->hdr.mxFrame;
Pgno iFrame;
/* Restore the clients cache of the wal-index header to the state it
** was in before the client began writing to the database.
*/
memcpy(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr));
for(iFrame=pWal->hdr.mxFrame+1;
ALWAYS(rc==SQLITE_OK) && iFrame<=iMax;
iFrame++
){
/* This call cannot fail. Unless the page for which the page number
** is passed as the second argument is (a) in the cache and
** (b) has an outstanding reference, then xUndo is either a no-op
** (if (a) is false) or simply expels the page from the cache (if (b)
** is false).
**
** If the upper layer is doing a rollback, it is guaranteed that there
** are no outstanding references to any page other than page 1. And
** page 1 is never written to the log until the transaction is
** committed. As a result, the call to xUndo may not fail.
*/
assert( walFramePgno(pWal, iFrame)!=1 );
rc = xUndo(pUndoCtx, walFramePgno(pWal, iFrame));
}
if( iMax!=pWal->hdr.mxFrame ) walCleanupHash(pWal);
}
return rc;
}
/*
** Argument aWalData must point to an array of WAL_SAVEPOINT_NDATA u32
** values. This function populates the array with values required to
** "rollback" the write position of the WAL handle back to the current
** point in the event of a savepoint rollback (via WalSavepointUndo()).
*/
void sqlite3WalSavepoint(Wal *pWal, u32 *aWalData){
assert( pWal->writeLock );
aWalData[0] = pWal->hdr.mxFrame;
aWalData[1] = pWal->hdr.aFrameCksum[0];
aWalData[2] = pWal->hdr.aFrameCksum[1];
aWalData[3] = pWal->nCkpt;
}
/*
** Move the write position of the WAL back to the point identified by
** the values in the aWalData[] array. aWalData must point to an array
** of WAL_SAVEPOINT_NDATA u32 values that has been previously populated
** by a call to WalSavepoint().
*/
int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData){
int rc = SQLITE_OK;
assert( pWal->writeLock );
assert( aWalData[3]!=pWal->nCkpt || aWalData[0]<=pWal->hdr.mxFrame );
if( aWalData[3]!=pWal->nCkpt ){
/* This savepoint was opened immediately after the write-transaction
** was started. Right after that, the writer decided to wrap around
** to the start of the log. Update the savepoint values to match.
*/
aWalData[0] = 0;
aWalData[3] = pWal->nCkpt;
}
if( aWalData[0]<pWal->hdr.mxFrame ){
pWal->hdr.mxFrame = aWalData[0];
pWal->hdr.aFrameCksum[0] = aWalData[1];
pWal->hdr.aFrameCksum[1] = aWalData[2];
walCleanupHash(pWal);
}
return rc;
}
/*
** This function is called just before writing a set of frames to the log
** file (see sqlite3WalFrames()). It checks to see if, instead of appending
** to the current log file, it is possible to overwrite the start of the
** existing log file with the new frames (i.e. "reset" the log). If so,
** it sets pWal->hdr.mxFrame to 0. Otherwise, pWal->hdr.mxFrame is left
** unchanged.
**
** SQLITE_OK is returned if no error is encountered (regardless of whether
** or not pWal->hdr.mxFrame is modified). An SQLite error code is returned
** if an error occurs.
*/
static int walRestartLog(Wal *pWal){
int rc = SQLITE_OK;
int cnt;
if( pWal->readLock==0 ){
volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
assert( pInfo->nBackfill==pWal->hdr.mxFrame );
if( pInfo->nBackfill>0 ){
u32 salt1;
sqlite3_randomness(4, &salt1);
rc = walLockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
if( rc==SQLITE_OK ){
/* If all readers are using WAL_READ_LOCK(0) (in other words if no
** readers are currently using the WAL), then the transactions
** frames will overwrite the start of the existing log. Update the
** wal-index header to reflect this.
**
** In theory it would be Ok to update the cache of the header only
** at this point. But updating the actual wal-index header is also
** safe and means there is no special case for sqlite3WalUndo()
** to handle if this transaction is rolled back. */
walRestartHdr(pWal, salt1);
walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
}else if( rc!=SQLITE_BUSY ){
return rc;
}
}
walUnlockShared(pWal, WAL_READ_LOCK(0));
pWal->readLock = -1;
cnt = 0;
do{
int notUsed;
rc = walTryBeginRead(pWal, &notUsed, 1, ++cnt);
}while( rc==WAL_RETRY );
assert( (rc&0xff)!=SQLITE_BUSY ); /* BUSY not possible when useWal==1 */
testcase( (rc&0xff)==SQLITE_IOERR );
testcase( rc==SQLITE_PROTOCOL );
testcase( rc==SQLITE_OK );
}
return rc;
}
/*
** Information about the current state of the WAL file and where
** the next fsync should occur - passed from sqlite3WalFrames() into
** walWriteToLog().
*/
typedef struct WalWriter {
Wal *pWal; /* The complete WAL information */
sqlite3_file *pFd; /* The WAL file to which we write */
sqlite3_int64 iSyncPoint; /* Fsync at this offset */
int syncFlags; /* Flags for the fsync */
int szPage; /* Size of one page */
} WalWriter;
/*
** Write iAmt bytes of content into the WAL file beginning at iOffset.
** Do a sync when crossing the p->iSyncPoint boundary.
**
** In other words, if iSyncPoint is in between iOffset and iOffset+iAmt,
** first write the part before iSyncPoint, then sync, then write the
** rest.
*/
static int walWriteToLog(
WalWriter *p, /* WAL to write to */
void *pContent, /* Content to be written */
int iAmt, /* Number of bytes to write */
sqlite3_int64 iOffset /* Start writing at this offset */
){
int rc;
if( iOffset<p->iSyncPoint && iOffset+iAmt>=p->iSyncPoint ){
int iFirstAmt = (int)(p->iSyncPoint - iOffset);
rc = sqlite3OsWrite(p->pFd, pContent, iFirstAmt, iOffset);
if( rc ) return rc;
iOffset += iFirstAmt;
iAmt -= iFirstAmt;
pContent = (void*)(iFirstAmt + (char*)pContent);
assert( WAL_SYNC_FLAGS(p->syncFlags)!=0 );
rc = sqlite3OsSync(p->pFd, WAL_SYNC_FLAGS(p->syncFlags));
if( iAmt==0 || rc ) return rc;
}
rc = sqlite3OsWrite(p->pFd, pContent, iAmt, iOffset);
return rc;
}
/*
** Write out a single frame of the WAL
*/
static int walWriteOneFrame(
WalWriter *p, /* Where to write the frame */
PgHdr *pPage, /* The page of the frame to be written */
int nTruncate, /* The commit flag. Usually 0. >0 for commit */
sqlite3_int64 iOffset /* Byte offset at which to write */
){
int rc; /* Result code from subfunctions */
void *pData; /* Data actually written */
u8 aFrame[WAL_FRAME_HDRSIZE]; /* Buffer to assemble frame-header in */
#if defined(SQLITE_HAS_CODEC)
if( (pData = sqlite3PagerCodec(pPage))==0 ) return SQLITE_NOMEM_BKPT;
#else
pData = pPage->pData;
#endif
walEncodeFrame(p->pWal, pPage->pgno, nTruncate, pData, aFrame);
rc = walWriteToLog(p, aFrame, sizeof(aFrame), iOffset);
if( rc ) return rc;
/* Write the page data */
rc = walWriteToLog(p, pData, p->szPage, iOffset+sizeof(aFrame));
return rc;
}
/*
** This function is called as part of committing a transaction within which
** one or more frames have been overwritten. It updates the checksums for
** all frames written to the wal file by the current transaction starting
** with the earliest to have been overwritten.
**
** SQLITE_OK is returned if successful, or an SQLite error code otherwise.
*/
static int walRewriteChecksums(Wal *pWal, u32 iLast){
const int szPage = pWal->szPage;/* Database page size */
int rc = SQLITE_OK; /* Return code */
u8 *aBuf; /* Buffer to load data from wal file into */
u8 aFrame[WAL_FRAME_HDRSIZE]; /* Buffer to assemble frame-headers in */
u32 iRead; /* Next frame to read from wal file */
i64 iCksumOff;
aBuf = sqlite3_malloc(szPage + WAL_FRAME_HDRSIZE);
if( aBuf==0 ) return SQLITE_NOMEM_BKPT;
/* Find the checksum values to use as input for the recalculating the
** first checksum. If the first frame is frame 1 (implying that the current
** transaction restarted the wal file), these values must be read from the
** wal-file header. Otherwise, read them from the frame header of the
** previous frame. */
assert( pWal->iReCksum>0 );
if( pWal->iReCksum==1 ){
iCksumOff = 24;
}else{
iCksumOff = walFrameOffset(pWal->iReCksum-1, szPage) + 16;
}
rc = sqlite3OsRead(pWal->pWalFd, aBuf, sizeof(u32)*2, iCksumOff);
pWal->hdr.aFrameCksum[0] = sqlite3Get4byte(aBuf);
pWal->hdr.aFrameCksum[1] = sqlite3Get4byte(&aBuf[sizeof(u32)]);
iRead = pWal->iReCksum;
pWal->iReCksum = 0;
for(; rc==SQLITE_OK && iRead<=iLast; iRead++){
i64 iOff = walFrameOffset(iRead, szPage);
rc = sqlite3OsRead(pWal->pWalFd, aBuf, szPage+WAL_FRAME_HDRSIZE, iOff);
if( rc==SQLITE_OK ){
u32 iPgno, nDbSize;
iPgno = sqlite3Get4byte(aBuf);
nDbSize = sqlite3Get4byte(&aBuf[4]);
walEncodeFrame(pWal, iPgno, nDbSize, &aBuf[WAL_FRAME_HDRSIZE], aFrame);
rc = sqlite3OsWrite(pWal->pWalFd, aFrame, sizeof(aFrame), iOff);
}
}
sqlite3_free(aBuf);
return rc;
}
/*
** Write a set of frames to the log. The caller must hold the write-lock
** on the log file (obtained using sqlite3WalBeginWriteTransaction()).
*/
int sqlite3WalFrames(
Wal *pWal, /* Wal handle to write to */
int szPage, /* Database page-size in bytes */
PgHdr *pList, /* List of dirty pages to write */
Pgno nTruncate, /* Database size after this commit */
int isCommit, /* True if this is a commit */
int sync_flags /* Flags to pass to OsSync() (or 0) */
){
int rc; /* Used to catch return codes */
u32 iFrame; /* Next frame address */
PgHdr *p; /* Iterator to run through pList with. */
PgHdr *pLast = 0; /* Last frame in list */
int nExtra = 0; /* Number of extra copies of last page */
int szFrame; /* The size of a single frame */
i64 iOffset; /* Next byte to write in WAL file */
WalWriter w; /* The writer */
u32 iFirst = 0; /* First frame that may be overwritten */
WalIndexHdr *pLive; /* Pointer to shared header */
assert( pList );
assert( pWal->writeLock );
/* If this frame set completes a transaction, then nTruncate>0. If
** nTruncate==0 then this frame set does not complete the transaction. */
assert( (isCommit!=0)==(nTruncate!=0) );
#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
{ int cnt; for(cnt=0, p=pList; p; p=p->pDirty, cnt++){}
WALTRACE(("WAL%p: frame write begin. %d frames. mxFrame=%d. %s\n",
pWal, cnt, pWal->hdr.mxFrame, isCommit ? "Commit" : "Spill"));
}
#endif
pLive = (WalIndexHdr*)walIndexHdr(pWal);
if( memcmp(&pWal->hdr, (void *)pLive, sizeof(WalIndexHdr))!=0 ){
iFirst = pLive->mxFrame+1;
}
/* See if it is possible to write these frames into the start of the
** log file, instead of appending to it at pWal->hdr.mxFrame.
*/
if( SQLITE_OK!=(rc = walRestartLog(pWal)) ){
return rc;
}
/* If this is the first frame written into the log, write the WAL
** header to the start of the WAL file. See comments at the top of
** this source file for a description of the WAL header format.
*/
iFrame = pWal->hdr.mxFrame;
if( iFrame==0 ){
u8 aWalHdr[WAL_HDRSIZE]; /* Buffer to assemble wal-header in */
u32 aCksum[2]; /* Checksum for wal-header */
sqlite3Put4byte(&aWalHdr[0], (WAL_MAGIC | SQLITE_BIGENDIAN));
sqlite3Put4byte(&aWalHdr[4], WAL_MAX_VERSION);
sqlite3Put4byte(&aWalHdr[8], szPage);
sqlite3Put4byte(&aWalHdr[12], pWal->nCkpt);
if( pWal->nCkpt==0 ) sqlite3_randomness(8, pWal->hdr.aSalt);
memcpy(&aWalHdr[16], pWal->hdr.aSalt, 8);
walChecksumBytes(1, aWalHdr, WAL_HDRSIZE-2*4, 0, aCksum);
sqlite3Put4byte(&aWalHdr[24], aCksum[0]);
sqlite3Put4byte(&aWalHdr[28], aCksum[1]);
pWal->szPage = szPage;
pWal->hdr.bigEndCksum = SQLITE_BIGENDIAN;
pWal->hdr.aFrameCksum[0] = aCksum[0];
pWal->hdr.aFrameCksum[1] = aCksum[1];
pWal->truncateOnCommit = 1;
rc = sqlite3OsWrite(pWal->pWalFd, aWalHdr, sizeof(aWalHdr), 0);
WALTRACE(("WAL%p: wal-header write %s\n", pWal, rc ? "failed" : "ok"));
if( rc!=SQLITE_OK ){
return rc;
}
/* Sync the header (unless SQLITE_IOCAP_SEQUENTIAL is true or unless
** all syncing is turned off by PRAGMA synchronous=OFF). Otherwise
** an out-of-order write following a WAL restart could result in
** database corruption. See the ticket:
**
** https://sqlite.org/src/info/ff5be73dee
*/
if( pWal->syncHeader ){
rc = sqlite3OsSync(pWal->pWalFd, CKPT_SYNC_FLAGS(sync_flags));
if( rc ) return rc;
}
}
assert( (int)pWal->szPage==szPage );
/* Setup information needed to write frames into the WAL */
w.pWal = pWal;
w.pFd = pWal->pWalFd;
w.iSyncPoint = 0;
w.syncFlags = sync_flags;
w.szPage = szPage;
iOffset = walFrameOffset(iFrame+1, szPage);
szFrame = szPage + WAL_FRAME_HDRSIZE;
/* Write all frames into the log file exactly once */
for(p=pList; p; p=p->pDirty){
int nDbSize; /* 0 normally. Positive == commit flag */
/* Check if this page has already been written into the wal file by
** the current transaction. If so, overwrite the existing frame and
** set Wal.writeLock to WAL_WRITELOCK_RECKSUM - indicating that
** checksums must be recomputed when the transaction is committed. */
if( iFirst && (p->pDirty || isCommit==0) ){
u32 iWrite = 0;
VVA_ONLY(rc =) sqlite3WalFindFrame(pWal, p->pgno, &iWrite);
assert( rc==SQLITE_OK || iWrite==0 );
if( iWrite>=iFirst ){
i64 iOff = walFrameOffset(iWrite, szPage) + WAL_FRAME_HDRSIZE;
void *pData;
if( pWal->iReCksum==0 || iWrite<pWal->iReCksum ){
pWal->iReCksum = iWrite;
}
#if defined(SQLITE_HAS_CODEC)
if( (pData = sqlite3PagerCodec(p))==0 ) return SQLITE_NOMEM;
#else
pData = p->pData;
#endif
rc = sqlite3OsWrite(pWal->pWalFd, pData, szPage, iOff);
if( rc ) return rc;
p->flags &= ~PGHDR_WAL_APPEND;
continue;
}
}
iFrame++;
assert( iOffset==walFrameOffset(iFrame, szPage) );
nDbSize = (isCommit && p->pDirty==0) ? nTruncate : 0;
rc = walWriteOneFrame(&w, p, nDbSize, iOffset);
if( rc ) return rc;
pLast = p;
iOffset += szFrame;
p->flags |= PGHDR_WAL_APPEND;
}
/* Recalculate checksums within the wal file if required. */
if( isCommit && pWal->iReCksum ){
rc = walRewriteChecksums(pWal, iFrame);
if( rc ) return rc;
}
/* If this is the end of a transaction, then we might need to pad
** the transaction and/or sync the WAL file.
**
** Padding and syncing only occur if this set of frames complete a
** transaction and if PRAGMA synchronous=FULL. If synchronous==NORMAL
** or synchronous==OFF, then no padding or syncing are needed.
**
** If SQLITE_IOCAP_POWERSAFE_OVERWRITE is defined, then padding is not
** needed and only the sync is done. If padding is needed, then the
** final frame is repeated (with its commit mark) until the next sector
** boundary is crossed. Only the part of the WAL prior to the last
** sector boundary is synced; the part of the last frame that extends
** past the sector boundary is written after the sync.
*/
if( isCommit && WAL_SYNC_FLAGS(sync_flags)!=0 ){
int bSync = 1;
if( pWal->padToSectorBoundary ){
int sectorSize = sqlite3SectorSize(pWal->pWalFd);
w.iSyncPoint = ((iOffset+sectorSize-1)/sectorSize)*sectorSize;
bSync = (w.iSyncPoint==iOffset);
testcase( bSync );
while( iOffset<w.iSyncPoint ){
rc = walWriteOneFrame(&w, pLast, nTruncate, iOffset);
if( rc ) return rc;
iOffset += szFrame;
nExtra++;
}
}
if( bSync ){
assert( rc==SQLITE_OK );
rc = sqlite3OsSync(w.pFd, WAL_SYNC_FLAGS(sync_flags));
}
}
/* If this frame set completes the first transaction in the WAL and
** if PRAGMA journal_size_limit is set, then truncate the WAL to the
** journal size limit, if possible.
*/
if( isCommit && pWal->truncateOnCommit && pWal->mxWalSize>=0 ){
i64 sz = pWal->mxWalSize;
if( walFrameOffset(iFrame+nExtra+1, szPage)>pWal->mxWalSize ){
sz = walFrameOffset(iFrame+nExtra+1, szPage);
}
walLimitSize(pWal, sz);
pWal->truncateOnCommit = 0;
}
/* Append data to the wal-index. It is not necessary to lock the
** wal-index to do this as the SQLITE_SHM_WRITE lock held on the wal-index
** guarantees that there are no other writers, and no data that may
** be in use by existing readers is being overwritten.
*/
iFrame = pWal->hdr.mxFrame;
for(p=pList; p && rc==SQLITE_OK; p=p->pDirty){
if( (p->flags & PGHDR_WAL_APPEND)==0 ) continue;
iFrame++;
rc = walIndexAppend(pWal, iFrame, p->pgno);
}
while( rc==SQLITE_OK && nExtra>0 ){
iFrame++;
nExtra--;
rc = walIndexAppend(pWal, iFrame, pLast->pgno);
}
if( rc==SQLITE_OK ){
/* Update the private copy of the header. */
pWal->hdr.szPage = (u16)((szPage&0xff00) | (szPage>>16));
testcase( szPage<=32768 );
testcase( szPage>=65536 );
pWal->hdr.mxFrame = iFrame;
if( isCommit ){
pWal->hdr.iChange++;
pWal->hdr.nPage = nTruncate;
}
/* If this is a commit, update the wal-index header too. */
if( isCommit ){
walIndexWriteHdr(pWal);
pWal->iCallback = iFrame;
}
}
WALTRACE(("WAL%p: frame write %s\n", pWal, rc ? "failed" : "ok"));
return rc;
}
/*
** This routine is called to implement sqlite3_wal_checkpoint() and
** related interfaces.
**
** Obtain a CHECKPOINT lock and then backfill as much information as
** we can from WAL into the database.
**
** If parameter xBusy is not NULL, it is a pointer to a busy-handler
** callback. In this case this function runs a blocking checkpoint.
*/
int sqlite3WalCheckpoint(
Wal *pWal, /* Wal connection */
sqlite3 *db, /* Check this handle's interrupt flag */
int eMode, /* PASSIVE, FULL, RESTART, or TRUNCATE */
int (*xBusy)(void*), /* Function to call when busy */
void *pBusyArg, /* Context argument for xBusyHandler */
int sync_flags, /* Flags to sync db file with (or 0) */
int nBuf, /* Size of temporary buffer */
u8 *zBuf, /* Temporary buffer to use */
int *pnLog, /* OUT: Number of frames in WAL */
int *pnCkpt /* OUT: Number of backfilled frames in WAL */
){
int rc; /* Return code */
int isChanged = 0; /* True if a new wal-index header is loaded */
int eMode2 = eMode; /* Mode to pass to walCheckpoint() */
int (*xBusy2)(void*) = xBusy; /* Busy handler for eMode2 */
assert( pWal->ckptLock==0 );
assert( pWal->writeLock==0 );
/* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked
** in the SQLITE_CHECKPOINT_PASSIVE mode. */
assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 );
if( pWal->readOnly ) return SQLITE_READONLY;
WALTRACE(("WAL%p: checkpoint begins\n", pWal));
/* IMPLEMENTATION-OF: R-62028-47212 All calls obtain an exclusive
** "checkpoint" lock on the database file. */
rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
if( rc ){
/* EVIDENCE-OF: R-10421-19736 If any other process is running a
** checkpoint operation at the same time, the lock cannot be obtained and
** SQLITE_BUSY is returned.
** EVIDENCE-OF: R-53820-33897 Even if there is a busy-handler configured,
** it will not be invoked in this case.
*/
testcase( rc==SQLITE_BUSY );
testcase( xBusy!=0 );
return rc;
}
pWal->ckptLock = 1;
/* IMPLEMENTATION-OF: R-59782-36818 The SQLITE_CHECKPOINT_FULL, RESTART and
** TRUNCATE modes also obtain the exclusive "writer" lock on the database
** file.
**
** EVIDENCE-OF: R-60642-04082 If the writer lock cannot be obtained
** immediately, and a busy-handler is configured, it is invoked and the
** writer lock retried until either the busy-handler returns 0 or the
** lock is successfully obtained.
*/
if( eMode!=SQLITE_CHECKPOINT_PASSIVE ){
rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_WRITE_LOCK, 1);
if( rc==SQLITE_OK ){
pWal->writeLock = 1;
}else if( rc==SQLITE_BUSY ){
eMode2 = SQLITE_CHECKPOINT_PASSIVE;
xBusy2 = 0;
rc = SQLITE_OK;
}
}
/* Read the wal-index header. */
if( rc==SQLITE_OK ){
rc = walIndexReadHdr(pWal, &isChanged);
if( isChanged && pWal->pDbFd->pMethods->iVersion>=3 ){
sqlite3OsUnfetch(pWal->pDbFd, 0, 0);
}
}
/* Copy data from the log to the database file. */
if( rc==SQLITE_OK ){
if( pWal->hdr.mxFrame && walPagesize(pWal)!=nBuf ){
rc = SQLITE_CORRUPT_BKPT;
}else{
rc = walCheckpoint(pWal, db, eMode2, xBusy2, pBusyArg, sync_flags, zBuf);
}
/* If no error occurred, set the output variables. */
if( rc==SQLITE_OK || rc==SQLITE_BUSY ){
if( pnLog ) *pnLog = (int)pWal->hdr.mxFrame;
if( pnCkpt ) *pnCkpt = (int)(walCkptInfo(pWal)->nBackfill);
}
}
if( isChanged ){
/* If a new wal-index header was loaded before the checkpoint was
** performed, then the pager-cache associated with pWal is now
** out of date. So zero the cached wal-index header to ensure that
** next time the pager opens a snapshot on this database it knows that
** the cache needs to be reset.
*/
memset(&pWal->hdr, 0, sizeof(WalIndexHdr));
}
/* Release the locks. */
sqlite3WalEndWriteTransaction(pWal);
walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
pWal->ckptLock = 0;
WALTRACE(("WAL%p: checkpoint %s\n", pWal, rc ? "failed" : "ok"));
return (rc==SQLITE_OK && eMode!=eMode2 ? SQLITE_BUSY : rc);
}
/* Return the value to pass to a sqlite3_wal_hook callback, the
** number of frames in the WAL at the point of the last commit since
** sqlite3WalCallback() was called. If no commits have occurred since
** the last call, then return 0.
*/
int sqlite3WalCallback(Wal *pWal){
u32 ret = 0;
if( pWal ){
ret = pWal->iCallback;
pWal->iCallback = 0;
}
return (int)ret;
}
/*
** This function is called to change the WAL subsystem into or out
** of locking_mode=EXCLUSIVE.
**
** If op is zero, then attempt to change from locking_mode=EXCLUSIVE
** into locking_mode=NORMAL. This means that we must acquire a lock
** on the pWal->readLock byte. If the WAL is already in locking_mode=NORMAL
** or if the acquisition of the lock fails, then return 0. If the
** transition out of exclusive-mode is successful, return 1. This
** operation must occur while the pager is still holding the exclusive
** lock on the main database file.
**
** If op is one, then change from locking_mode=NORMAL into
** locking_mode=EXCLUSIVE. This means that the pWal->readLock must
** be released. Return 1 if the transition is made and 0 if the
** WAL is already in exclusive-locking mode - meaning that this
** routine is a no-op. The pager must already hold the exclusive lock
** on the main database file before invoking this operation.
**
** If op is negative, then do a dry-run of the op==1 case but do
** not actually change anything. The pager uses this to see if it
** should acquire the database exclusive lock prior to invoking
** the op==1 case.
*/
int sqlite3WalExclusiveMode(Wal *pWal, int op){
int rc;
assert( pWal->writeLock==0 );
assert( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE || op==-1 );
/* pWal->readLock is usually set, but might be -1 if there was a
** prior error while attempting to acquire are read-lock. This cannot
** happen if the connection is actually in exclusive mode (as no xShmLock
** locks are taken in this case). Nor should the pager attempt to
** upgrade to exclusive-mode following such an error.
*/
assert( pWal->readLock>=0 || pWal->lockError );
assert( pWal->readLock>=0 || (op<=0 && pWal->exclusiveMode==0) );
if( op==0 ){
if( pWal->exclusiveMode!=WAL_NORMAL_MODE ){
pWal->exclusiveMode = WAL_NORMAL_MODE;
if( walLockShared(pWal, WAL_READ_LOCK(pWal->readLock))!=SQLITE_OK ){
pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
}
rc = pWal->exclusiveMode==WAL_NORMAL_MODE;
}else{
/* Already in locking_mode=NORMAL */
rc = 0;
}
}else if( op>0 ){
assert( pWal->exclusiveMode==WAL_NORMAL_MODE );
assert( pWal->readLock>=0 );
walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
rc = 1;
}else{
rc = pWal->exclusiveMode==WAL_NORMAL_MODE;
}
return rc;
}
/*
** Return true if the argument is non-NULL and the WAL module is using
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false.
*/
int sqlite3WalHeapMemory(Wal *pWal){
return (pWal && pWal->exclusiveMode==WAL_HEAPMEMORY_MODE );
}
#ifdef SQLITE_ENABLE_SNAPSHOT
/* Create a snapshot object. The content of a snapshot is opaque to
** every other subsystem, so the WAL module can put whatever it needs
** in the object.
*/
int sqlite3WalSnapshotGet(Wal *pWal, sqlite3_snapshot **ppSnapshot){
int rc = SQLITE_OK;
WalIndexHdr *pRet;
static const u32 aZero[4] = { 0, 0, 0, 0 };
assert( pWal->readLock>=0 && pWal->writeLock==0 );
if( memcmp(&pWal->hdr.aFrameCksum[0],aZero,16)==0 ){
*ppSnapshot = 0;
return SQLITE_ERROR;
}
pRet = (WalIndexHdr*)sqlite3_malloc(sizeof(WalIndexHdr));
if( pRet==0 ){
rc = SQLITE_NOMEM_BKPT;
}else{
memcpy(pRet, &pWal->hdr, sizeof(WalIndexHdr));
*ppSnapshot = (sqlite3_snapshot*)pRet;
}
return rc;
}
/* Try to open on pSnapshot when the next read-transaction starts
*/
void sqlite3WalSnapshotOpen(Wal *pWal, sqlite3_snapshot *pSnapshot){
pWal->pSnapshot = (WalIndexHdr*)pSnapshot;
}
/*
** Return a +ve value if snapshot p1 is newer than p2. A -ve value if
** p1 is older than p2 and zero if p1 and p2 are the same snapshot.
*/
int sqlite3_snapshot_cmp(sqlite3_snapshot *p1, sqlite3_snapshot *p2){
WalIndexHdr *pHdr1 = (WalIndexHdr*)p1;
WalIndexHdr *pHdr2 = (WalIndexHdr*)p2;
/* aSalt[0] is a copy of the value stored in the wal file header. It
** is incremented each time the wal file is restarted. */
if( pHdr1->aSalt[0]<pHdr2->aSalt[0] ) return -1;
if( pHdr1->aSalt[0]>pHdr2->aSalt[0] ) return +1;
if( pHdr1->mxFrame<pHdr2->mxFrame ) return -1;
if( pHdr1->mxFrame>pHdr2->mxFrame ) return +1;
return 0;
}
#endif /* SQLITE_ENABLE_SNAPSHOT */
#ifdef SQLITE_ENABLE_ZIPVFS
/*
** If the argument is not NULL, it points to a Wal object that holds a
** read-lock. This function returns the database page-size if it is known,
** or zero if it is not (or if pWal is NULL).
*/
int sqlite3WalFramesize(Wal *pWal){
assert( pWal==0 || pWal->readLock>=0 );
return (pWal ? pWal->szPage : 0);
}
#endif
/* Return the sqlite3_file object for the WAL file
*/
sqlite3_file *sqlite3WalFile(Wal *pWal){
return pWal->pWalFd;
}
#endif /* #ifndef SQLITE_OMIT_WAL */
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