Enhance the pcache1 page cache so that it tries to allocate a block of

SQLITE_DEFAULT_PCACHE_INITSZ pages from malloc() on startup, and uses those preallocated pages when possible rather than going to malloc() for each individual page. About a 5% performance increase for some workloads. FossilOrigin-Name: 5348ffc3fda5168c1e9e14aa88b0c6aedbda7c94
2015-07-08 16:22:42 +00:00
parent 4698136594 7b341e6f99
commit 104a25a034
10 changed files with 196 additions and 104 deletions
@@ -1,5 +1,5 @@
-C Early\sdetection\sof\sfile\scorruption\sin\sa\sdebugging\sroutine,\sbefore\sthe\sinvalid\ndata\scan\scause\sproblems.
-D 2015-07-08T12:25:38.106
+C Enhance\sthe\spcache1\spage\scache\sso\sthat\sit\stries\sto\sallocate\sa\sblock\sof\nSQLITE_DEFAULT_PCACHE_INITSZ\spages\sfrom\smalloc()\son\sstartup,\sand\suses\sthose\npreallocated\spages\swhen\spossible\srather\sthan\sgoing\sto\smalloc()\sfor\seach\nindividual\spage.\s\sAbout\sa\s5%\sperformance\sincrease\sfor\ssome\sworkloads.
+D 2015-07-08T16:22:42.453
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 017bf0511d1b2dd1db5e16488fbf75a17b526cbc
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -269,7 +269,7 @@ F src/auth.c b56c78ebe40a2110fd361379f7e8162d23f92240
 F src/backup.c 4d9134dc988a87838c06056c89c0e8c4700a0452
 F src/bitvec.c d1f21d7d91690747881f03940584f4cc548c9d3d
 F src/btmutex.c 45a968cc85afed9b5e6cf55bf1f42f8d18107f79
-F src/btree.c 740ab30df845f4a2c2bdb731ed191b4b63b2b2eb
+F src/btree.c 781deff0d5af639e8dd4f83ec963cc3bbf8cffc2
 F src/btree.h 969adc948e89e449220ff0ff724c94bb2a52e9f1
 F src/btreeInt.h 2ad754dd4528baa8d0946a593cc373b890bf859e
 F src/build.c b3f15255d5b16e42dafeaa638fd4f8a47c94ed70
@@ -283,7 +283,7 @@ F src/expr.c c5c58e4d01c7ceb2266791d8d877f1b23a88e316
 F src/fault.c 160a0c015b6c2629d3899ed2daf63d75754a32bb
 F src/fkey.c c9b63a217d86582c22121699a47f22f524608869
 F src/func.c a98ea5880dc50e9ca6dd6f57079a37b9cfcdecf1
-F src/global.c 4f77cadbc5427d00139ba43d0f3979804cbb700e
+F src/global.c 508e4087f7b41d688e4762dcf4d4fe28cfbc87f9
 F src/hash.c 4263fbc955f26c2e8cdc0cf214bc42435aa4e4f5
 F src/hash.h c8f3c31722cf3277d03713909761e152a5b81094
 F src/hwtime.h d32741c8f4df852c7d959236615444e2b1063b08
@@ -319,7 +319,7 @@ F src/pager.h 6d435f563b3f7fcae4b84433b76a6ac2730036e2
 F src/parse.y 6d60dda8f8d418b6dc034f1fbccd816c459983a8
 F src/pcache.c cde06aa50962595e412d497e22fd2e07878ba1f0
 F src/pcache.h 9968603796240cdf83da7e7bef76edf90619cea9
-F src/pcache1.c b800e90896640bb0d1b0f6baa34fb059ca3b8b2e
+F src/pcache1.c 3f4c87cf913f2de8189026d9a5223ddaf55eaf6b
 F src/pragma.c c1f4d012ea9f6b1ce52d341b2cd0ad72d560afd7
 F src/pragma.h b8632d7cdda7b25323fa580e3e558a4f0d4502cc
 F src/prepare.c 82e5db1013846a819f198336fed72c44c974e7b1
@@ -332,7 +332,7 @@ F src/shell.c 8af3cced094aebb5f57a8ad739b9dafc7867eed7
 F src/sqlite.h.in 3d951bf985839de7fcf4d3f69568bb4df2641abe
 F src/sqlite3.rc 992c9f5fb8285ae285d6be28240a7e8d3a7f2bad
 F src/sqlite3ext.h be1a718b7d2ce40ceba725ae92c8eb5f18003066
-F src/sqliteInt.h bc2cb1755150fc0b490d1af23ac2911b03f2f92d
+F src/sqliteInt.h d8d420d66a5c403b119696159b69f71cd53840ce
 F src/sqliteLimit.h 216557999cb45f2e3578ed53ebefe228d779cb46
 F src/status.c f266ad8a2892d659b74f0f50cb6a88b6e7c12179
 F src/table.c 51b46b2a62d1b3a959633d593b89bab5e2c9155e
@@ -843,9 +843,9 @@ F test/mallocL.test 252ddc7eb4fbf75364eab17b938816085ff1fc17
 F test/malloc_common.tcl aac62499b76be719fac31e7a3e54a7fd53272e7f
 F test/manydb.test 28385ae2087967aa05c38624cec7d96ec74feb3e
 F test/mem5.test c6460fba403c5703141348cd90de1c294188c68f
-F test/memdb.test fcb5297b321b562084fc79d64d5a12a1cd2b639b
+F test/memdb.test c1f2a343ad14398d5d6debda6ea33e80d0dafcc7
 F test/memleak.test 10b9c6c57e19fc68c32941495e9ba1c50123f6e2
-F test/memsubsys1.test 690d142525a7d31efb638b0d232e25fac3afeb1a
+F test/memsubsys1.test 1733c617e246642db5bf3b9f78c18e2b14fac96c
 F test/memsubsys2.test 3a1c1a9de48e5726faa85108b02459fae8cb9ee9
 F test/minmax.test 42fbad0e81afaa6e0de41c960329f2b2c3526efd
 F test/minmax2.test b44bae787fc7b227597b01b0ca5575c7cb54d3bc
@@ -900,7 +900,7 @@ F test/pagerfault3.test 1003fcda009bf48a8e22a516e193b6ef0dd1bbd8
 F test/pageropt.test 6b8f6a123a5572c195ad4ae40f2987007923bbd6
 F test/pagesize.test 5769fc62d8c890a83a503f67d47508dfdc543305
 F test/pcache.test b09104b03160aca0d968d99e8cd2c5b1921a993d
-F test/pcache2.test a83efe2dec0d392f814bfc998def1d1833942025
+F test/pcache2.test ec3ae192f444ee6a0a80d1fd80d99695d884bfb3
 F test/percentile.test 4243af26b8f3f4555abe166f723715a1f74c77ff
 F test/permutations.test 6a88fd9ca15b804e9c20990773262ca67494058f
 F test/pragma.test be7195f0aa72bdb8a512133e9640ac40f15b57a2
@@ -1005,7 +1005,7 @@ F test/speed3.test d32043614c08c53eafdc80f33191d5bd9b920523
 F test/speed4.test abc0ad3399dcf9703abed2fff8705e4f8e416715
 F test/speed4p.explain 6b5f104ebeb34a038b2f714150f51d01143e59aa
 F test/speed4p.test 0e51908951677de5a969b723e03a27a1c45db38b
-F test/speedtest1.c 2e8f367c5fe5e0c3df24a157e17cb2f75c1b88c7
+F test/speedtest1.c 54f211994e2fb5b3f7c5c82137378f46ca89aae8
 F test/spellfix.test 0597065ff57042df1f138e6a2611ae19c2698135
 F test/sqldiff1.test 8f6bc7c6a5b3585d350d779c6078869ba402f8f5
 F test/sqllimits1.test e05786eaed7950ff6a2d00031d001d8a26131e68
@@ -1364,7 +1364,8 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 48bd54594752d5be3337f12c72f28d2080cb630b
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 6ace73541ae48aeb19e0c2d9f6772d032d0a7eae
-R 8adde983bcb4c45839c171b768ffd3b9
+P b27a47fef995f0ab2516e6ca779711cab1f50fb9 c1e2ed0ef4d3436d19d3203c5fb553caac53659e
+R 0716d0744f0e72c8cdadbca41133bc14
+T +closed c1e2ed0ef4d3436d19d3203c5fb553caac53659e
 U drh
-Z b9cf714cb314f182c61af66a54b1bb68
+Z eea1350426d30f63377f69d37a46ee1a
@@ -1 +1 @@
-b27a47fef995f0ab2516e6ca779711cab1f50fb9
+5348ffc3fda5168c1e9e14aa88b0c6aedbda7c94
@@ -9119,7 +9119,7 @@ static int checkTreePage(
      assert( (u32)i<=usableSize-4 );     /* Enforced by btreeInitPage() */
      size = get2byte(&data[i+2]);
      assert( (u32)(i+size)<=usableSize );  /* Enforced by btreeInitPage() */
-      btreeHeapInsert(heap, (i<<16)|(i+size-1));
+      btreeHeapInsert(heap, (((u32)i)<<16)|(i+size-1));
      /* EVIDENCE-OF: R-58208-19414 The first 2 bytes of a freeblock are a
      ** big-endian integer which is the offset in the b-tree page of the next
      ** freeblock in the chain, or zero if the freeblock is the last on the
@@ -186,7 +186,7 @@ SQLITE_WSD struct Sqlite3Config sqlite3Config = {
   0,                         /* nScratch */
   (void*)0,                  /* pPage */
   0,                         /* szPage */
-   0,                         /* nPage */
+   SQLITE_DEFAULT_PCACHE_INITSZ, /* nPage */
   0,                         /* mxParserStack */
   0,                         /* sharedCacheEnabled */
   SQLITE_SORTER_PMASZ,       /* szPma */
@@ -41,7 +41,8 @@
 **
 ** If SQLITE_PCACHE_SEPARATE_HEADER is defined, then the extension is obtained
 ** using a separate memory allocation from the database page content.  This
-** seeks to overcome the "clownfoot" problem of allocating a few bytes more
+** seeks to overcome the "clownshoe" problem (also called "internal
+** fragmentation" in academic literature) of allocating a few bytes more
 ** than a power of two with the memory allocator rounding up to the next
 ** power of two, and leaving the rounded-up space unused.
 **
@@ -50,8 +51,35 @@
 **
 ** The pcache.c and pager.c modules deal pointers to PgHdr objects.
 ** The btree.c module deals with pointers to MemPage objects.
+**
+** SOURCE OF PAGE CACHE MEMORY:
+**
+** Memory for a page might come from any of three sources:
+**
+**    (1)  The general-purpose memory allocator - sqlite3Malloc()
+**    (2)  Global page-cache memory provided using sqlite3_config() with
+**         SQLITE_CONFIG_PAGECACHE.
+**    (3)  PCache-local bulk allocation.
+**
+** The third case is a chunk of heap memory (defaulting to 100 pages worth)
+** that is allocated when the page cache is created.  The size of the local
+** bulk allocation can be adjusted using 
+**
+**     sqlite3_config(SQLITE_CONFIG_PCACHE, 0, 0, N).
+**
+** If N is positive, then N pages worth of memory are allocated using a single
+** sqlite3Malloc() call and that memory is used for the first N pages allocated.
+** Or if N is negative, then -1024*N bytes of memory are allocated and used
+** for as many pages as can be accomodated.
+**
+** Only one of (2) or (3) can be used.  Once the memory available to (2) or
+** (3) is exhausted, subsequent allocations fail over to the general-purpose
+** memory allocator (1).
+**
+** Earlier versions of SQLite used only methods (1) and (2).  But experiments
+** show that method (3) with N==100 provides about a 5% performance boost for
+** common workloads.
 */
-
 #include "sqliteInt.h"

 typedef struct PCache1 PCache1;
@@ -105,8 +133,9 @@ struct PCache1 {
  ** The PGroup mutex must be held when accessing nMax.
  */
  PGroup *pGroup;                     /* PGroup this cache belongs to */
-  int szPage;                         /* Size of allocated pages in bytes */
-  int szExtra;                        /* Size of extra space in bytes */
+  int szPage;                         /* Size of database content section */
+  int szExtra;                        /* sizeof(MemPage)+sizeof(PgHdr) */
+  int szAlloc;                        /* Total size of one pcache line */
  int bPurgeable;                     /* True if cache is purgeable */
  unsigned int nMin;                  /* Minimum number of pages reserved */
  unsigned int nMax;                  /* Configured "cache_size" value */
@@ -120,6 +149,8 @@ struct PCache1 {
  unsigned int nPage;                 /* Total number of pages in apHash */
  unsigned int nHash;                 /* Number of slots in apHash[] */
  PgHdr1 **apHash;                    /* Hash table for fast lookup by key */
+  PgHdr1 *pFree;                      /* List of unused pcache-local pages */
+  void *pBulk;                        /* Bulk memory used by pcache-local */
 };

 /*
@@ -132,6 +163,7 @@ struct PgHdr1 {
  sqlite3_pcache_page page;
  unsigned int iKey;             /* Key value (page number) */
  u8 isPinned;                   /* Page in use, not on the LRU list */
+  u8 isBulkLocal;                /* This page from bulk local storage */
  PgHdr1 *pNext;                 /* Next in hash table chain */
  PCache1 *pCache;               /* Cache that currently owns this page */
  PgHdr1 *pLruNext;              /* Next in LRU list of unpinned pages */
@@ -139,8 +171,8 @@ struct PgHdr1 {
 };

 /*
-** Free slots in the allocator used to divide up the buffer provided using
-** the SQLITE_CONFIG_PAGECACHE mechanism.
+** Free slots in the allocator used to divide up the global page cache
+** buffer provided using the SQLITE_CONFIG_PAGECACHE mechanism.
 */
 struct PgFreeslot {
  PgFreeslot *pNext;  /* Next free slot */
@@ -158,10 +190,11 @@ static SQLITE_WSD struct PCacheGlobal {
  ** The nFreeSlot and pFree values do require mutex protection.
  */
  int isInit;                    /* True if initialized */
+  int separateCache;             /* Use a new PGroup for each PCache */
  int szSlot;                    /* Size of each free slot */
  int nSlot;                     /* The number of pcache slots */
  int nReserve;                  /* Try to keep nFreeSlot above this */
-  void *pStart, *pEnd;           /* Bounds of pagecache malloc range */
+  void *pStart, *pEnd;           /* Bounds of global page cache memory */
  /* Above requires no mutex.  Use mutex below for variable that follow. */
  sqlite3_mutex *mutex;          /* Mutex for accessing the following: */
  PgFreeslot *pFree;             /* Free page blocks */
@@ -208,6 +241,7 @@ static SQLITE_WSD struct PCacheGlobal {
 void sqlite3PCacheBufferSetup(void *pBuf, int sz, int n){
  if( pcache1.isInit ){
    PgFreeslot *p;
+    if( pBuf==0 ) sz = n = 0;
    sz = ROUNDDOWN8(sz);
    pcache1.szSlot = sz;
    pcache1.nSlot = pcache1.nFreeSlot = n;
@@ -272,9 +306,9 @@ static void *pcache1Alloc(int nByte){
 /*
 ** Free an allocated buffer obtained from pcache1Alloc().
 */
-static int pcache1Free(void *p){
+static void pcache1Free(void *p){
  int nFreed = 0;
-  if( p==0 ) return 0;
+  if( p==0 ) return;
  if( p>=pcache1.pStart && p<pcache1.pEnd ){
    PgFreeslot *pSlot;
    sqlite3_mutex_enter(pcache1.mutex);
@@ -289,15 +323,14 @@ static int pcache1Free(void *p){
  }else{
    assert( sqlite3MemdebugHasType(p, MEMTYPE_PCACHE) );
    sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
-    nFreed = sqlite3MallocSize(p);
 #ifndef SQLITE_DISABLE_PAGECACHE_OVERFLOW_STATS
+    nFreed = sqlite3MallocSize(p);
    sqlite3_mutex_enter(pcache1.mutex);
    sqlite3StatusDown(SQLITE_STATUS_PAGECACHE_OVERFLOW, nFreed);
    sqlite3_mutex_leave(pcache1.mutex);
 #endif
    sqlite3_free(p);
  }
-  return nFreed;
 }

 #ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
@@ -325,54 +358,65 @@ static PgHdr1 *pcache1AllocPage(PCache1 *pCache){
  PgHdr1 *p = 0;
  void *pPg;

-  /* The group mutex must be released before pcache1Alloc() is called. This
-  ** is because it may call sqlite3_release_memory(), which assumes that 
-  ** this mutex is not held. */
  assert( sqlite3_mutex_held(pCache->pGroup->mutex) );
-  pcache1LeaveMutex(pCache->pGroup);
-#ifdef SQLITE_PCACHE_SEPARATE_HEADER
-  pPg = pcache1Alloc(pCache->szPage);
-  p = sqlite3Malloc(sizeof(PgHdr1) + pCache->szExtra);
-  if( !pPg || !p ){
-    pcache1Free(pPg);
-    sqlite3_free(p);
-    pPg = 0;
-  }
-#else
-  pPg = pcache1Alloc(ROUND8(sizeof(PgHdr1)) + pCache->szPage + pCache->szExtra);
-  p = (PgHdr1 *)&((u8 *)pPg)[pCache->szPage];
+  if( pCache->pFree ){
+    p = pCache->pFree;
+    pCache->pFree = p->pNext;
+    p->pNext = 0;
+  }else{
+#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
+    /* The group mutex must be released before pcache1Alloc() is called. This
+    ** is because it might call sqlite3_release_memory(), which assumes that 
+    ** this mutex is not held. */
+    assert( pcache1.separateCache==0 );
+    assert( pCache->pGroup==&pcache1.grp );
+    pcache1LeaveMutex(pCache->pGroup);
 #endif
-  pcache1EnterMutex(pCache->pGroup);
-
-  if( pPg ){
+#ifdef SQLITE_PCACHE_SEPARATE_HEADER
+    pPg = pcache1Alloc(pCache->szPage);
+    p = sqlite3Malloc(sizeof(PgHdr1) + pCache->szExtra);
+    if( !pPg || !p ){
+      pcache1Free(pPg);
+      sqlite3_free(p);
+      pPg = 0;
+    }
+#else
+    pPg = pcache1Alloc(pCache->szAlloc);
+    p = (PgHdr1 *)&((u8 *)pPg)[pCache->szPage];
+#endif
+#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
+    pcache1EnterMutex(pCache->pGroup);
+#endif
+    if( pPg==0 ) return 0;
    p->page.pBuf = pPg;
    p->page.pExtra = &p[1];
-    if( pCache->bPurgeable ){
-      pCache->pGroup->nCurrentPage++;
-    }
-    return p;
+    p->isBulkLocal = 0;
  }
-  return 0;
+  if( pCache->bPurgeable ){
+    pCache->pGroup->nCurrentPage++;
+  }
+  return p;
 }

 /*
 ** Free a page object allocated by pcache1AllocPage().
-**
-** The pointer is allowed to be NULL, which is prudent.  But it turns out
-** that the current implementation happens to never call this routine
-** with a NULL pointer, so we mark the NULL test with ALWAYS().
 */
 static void pcache1FreePage(PgHdr1 *p){
-  if( ALWAYS(p) ){
-    PCache1 *pCache = p->pCache;
-    assert( sqlite3_mutex_held(p->pCache->pGroup->mutex) );
+  PCache1 *pCache;
+  assert( p!=0 );
+  pCache = p->pCache;
+  assert( sqlite3_mutex_held(p->pCache->pGroup->mutex) );
+  if( p->isBulkLocal ){
+    p->pNext = pCache->pFree;
+    pCache->pFree = p;
+  }else{
    pcache1Free(p->page.pBuf);
 #ifdef SQLITE_PCACHE_SEPARATE_HEADER
    sqlite3_free(p);
 #endif
-    if( pCache->bPurgeable ){
-      pCache->pGroup->nCurrentPage--;
-    }
+  }
+  if( pCache->bPurgeable ){
+    pCache->pGroup->nCurrentPage--;
  }
 }

@@ -572,6 +616,31 @@ static int pcache1Init(void *NotUsed){
  UNUSED_PARAMETER(NotUsed);
  assert( pcache1.isInit==0 );
  memset(&pcache1, 0, sizeof(pcache1));
+
+
+  /*
+  ** The pcache1.separateCache variable is true if each PCache has its own
+  ** private PGroup (mode-1).  pcache1.separateCache is false if the single
+  ** PGroup in pcache1.grp is used for all page caches (mode-2).
+  **
+  **   *  Always use a unified cache (mode-2) if ENABLE_MEMORY_MANAGEMENT
+  **
+  **   *  Use a unified cache in single-threaded applications that have
+  **      configured a start-time buffer for use as page-cache memory using
+  **      sqlite3_config(SQLITE_CONFIG_PAGECACHE, pBuf, sz, N) with non-NULL 
+  **      pBuf argument.
+  **
+  **   *  Otherwise use separate caches (mode-1)
+  */
+#if defined(SQLITE_ENABLE_MEMORY_MANAGEMENT)
+  pcache1.separateCache = 0;
+#elif SQLITE_THREADSAFE
+  pcache1.separateCache = sqlite3GlobalConfig.pPage==0
+                          || sqlite3GlobalConfig.bCoreMutex>0;
+#else
+  pcache1.separateCache = sqlite3GlobalConfig.pPage==0;
+#endif
+
 #if SQLITE_THREADSAFE
  if( sqlite3GlobalConfig.bCoreMutex ){
    pcache1.grp.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_LRU);
@@ -607,31 +676,13 @@ static sqlite3_pcache *pcache1Create(int szPage, int szExtra, int bPurgeable){
  PGroup *pGroup;       /* The group the new page cache will belong to */
  int sz;               /* Bytes of memory required to allocate the new cache */

-  /*
-  ** The separateCache variable is true if each PCache has its own private
-  ** PGroup.  In other words, separateCache is true for mode (1) where no
-  ** mutexing is required.
-  **
-  **   *  Always use a unified cache (mode-2) if ENABLE_MEMORY_MANAGEMENT
-  **
-  **   *  Always use a unified cache in single-threaded applications
-  **
-  **   *  Otherwise (if multi-threaded and ENABLE_MEMORY_MANAGEMENT is off)
-  **      use separate caches (mode-1)
-  */
-#if defined(SQLITE_ENABLE_MEMORY_MANAGEMENT) || SQLITE_THREADSAFE==0
-  const int separateCache = 0;
-#else
-  int separateCache = sqlite3GlobalConfig.bCoreMutex>0;
-#endif
-
  assert( (szPage & (szPage-1))==0 && szPage>=512 && szPage<=65536 );
  assert( szExtra < 300 );

-  sz = sizeof(PCache1) + sizeof(PGroup)*separateCache;
+  sz = sizeof(PCache1) + sizeof(PGroup)*pcache1.separateCache;
  pCache = (PCache1 *)sqlite3MallocZero(sz);
  if( pCache ){
-    if( separateCache ){
+    if( pcache1.separateCache ){
      pGroup = (PGroup*)&pCache[1];
      pGroup->mxPinned = 10;
    }else{
@@ -640,6 +691,7 @@ static sqlite3_pcache *pcache1Create(int szPage, int szExtra, int bPurgeable){
    pCache->pGroup = pGroup;
    pCache->szPage = szPage;
    pCache->szExtra = szExtra;
+    pCache->szAlloc = szPage + szExtra + ROUND8(sizeof(PgHdr1));
    pCache->bPurgeable = (bPurgeable ? 1 : 0);
    pcache1EnterMutex(pGroup);
    pcache1ResizeHash(pCache);
@@ -649,6 +701,36 @@ static sqlite3_pcache *pcache1Create(int szPage, int szExtra, int bPurgeable){
      pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage;
    }
    pcache1LeaveMutex(pGroup);
+    /* Try to initialize the local bulk pagecache line allocation if using
+    ** separate caches and if nPage!=0 */
+    if( pcache1.separateCache
+     && sqlite3GlobalConfig.nPage!=0
+     && sqlite3GlobalConfig.pPage==0
+    ){
+      int szBulk;
+      char *zBulk;
+      sqlite3BeginBenignMalloc();
+      if( sqlite3GlobalConfig.nPage>0 ){
+        szBulk = pCache->szAlloc * sqlite3GlobalConfig.nPage;
+      }else{
+        szBulk = -1024*sqlite3GlobalConfig.nPage;
+      }
+      zBulk = pCache->pBulk = sqlite3Malloc( szBulk );
+      sqlite3EndBenignMalloc();
+      if( zBulk ){
+        int nBulk = sqlite3MallocSize(zBulk)/pCache->szAlloc;
+        int i;
+        for(i=0; i<nBulk; i++){
+          PgHdr1 *pX = (PgHdr1*)&zBulk[szPage];
+          pX->page.pBuf = zBulk;
+          pX->page.pExtra = &pX[1];
+          pX->isBulkLocal = 1;
+          pX->pNext = pCache->pFree;
+          pCache->pFree = pX;
+          zBulk += pCache->szAlloc;
+        }
+      }
+    }
    if( pCache->nHash==0 ){
      pcache1Destroy((sqlite3_pcache*)pCache);
      pCache = 0;
@@ -742,26 +824,17 @@ static SQLITE_NOINLINE PgHdr1 *pcache1FetchStage2(
  assert( pCache->nHash>0 && pCache->apHash );

  /* Step 4. Try to recycle a page. */
-  if( pCache->bPurgeable && pGroup->pLruTail && (
-         (pCache->nPage+1>=pCache->nMax)
-      || pGroup->nCurrentPage>=pGroup->nMaxPage
-      || pcache1UnderMemoryPressure(pCache)
-  )){
+  if( pCache->bPurgeable
+   && pGroup->pLruTail
+   && ((pCache->nPage+1>=pCache->nMax) || pcache1UnderMemoryPressure(pCache))
+  ){
    PCache1 *pOther;
    pPage = pGroup->pLruTail;
    assert( pPage->isPinned==0 );
    pcache1RemoveFromHash(pPage, 0);
    pcache1PinPage(pPage);
    pOther = pPage->pCache;
-
-    /* We want to verify that szPage and szExtra are the same for pOther
-    ** and pCache.  Assert that we can verify this by comparing sums. */
-    assert( (pCache->szPage & (pCache->szPage-1))==0 && pCache->szPage>=512 );
-    assert( pCache->szExtra<512 );
-    assert( (pOther->szPage & (pOther->szPage-1))==0 && pOther->szPage>=512 );
-    assert( pOther->szExtra<512 );
-
-    if( pOther->szPage+pOther->szExtra != pCache->szPage+pCache->szExtra ){
+    if( pOther->szAlloc != pCache->szAlloc ){
      pcache1FreePage(pPage);
      pPage = 0;
    }else{
@@ -1037,6 +1110,7 @@ static void pcache1Destroy(sqlite3_pcache *p){
  pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage;
  pcache1EnforceMaxPage(pGroup);
  pcache1LeaveMutex(pGroup);
+  sqlite3_free(pCache->pBulk);
  sqlite3_free(pCache->apHash);
  sqlite3_free(pCache);
 }
@@ -1092,7 +1166,7 @@ int sqlite3PcacheReleaseMemory(int nReq){
  int nFree = 0;
  assert( sqlite3_mutex_notheld(pcache1.grp.mutex) );
  assert( sqlite3_mutex_notheld(pcache1.mutex) );
-  if( pcache1.pStart==0 ){
+  if( sqlite3GlobalConfig.nPage==0 ){
    PgHdr1 *p;
    pcache1EnterMutex(&pcache1.grp);
    while( (nReq<0 || nFree<nReq) && ((p=pcache1.grp.pLruTail)!=0) ){
@@ -509,6 +509,16 @@
 # define SQLITE_MAX_WORKER_THREADS SQLITE_DEFAULT_WORKER_THREADS
 #endif

+/*
+** The default initial allocation for the pagecache when using separate
+** pagecaches for each database connection.  A positive number is the
+** number of pages.  A negative number N translations means that a buffer
+** of -1024*N bytes is allocated and used for as many pages as it will hold.
+*/
+#ifndef SQLITE_DEFAULT_PCACHE_INITSZ
+# define SQLITE_DEFAULT_PCACHE_INITSZ 100
+#endif
+

 /*
 ** GCC does not define the offsetof() macro so we'll have to do it
@@ -419,11 +419,10 @@ ifcapable autovacuum {
      INSERT INTO t1 VALUES(randstr(1000,1000));
      INSERT INTO t1 VALUES(randstr(1000,1000));
    }
-    set memused [lindex [sqlite3_status SQLITE_STATUS_MEMORY_USED 0] 1]
-    set pgovfl [lindex [sqlite3_status SQLITE_STATUS_PAGECACHE_OVERFLOW 0] 1]
+    set before [db one {PRAGMA page_count}]
    execsql { DELETE FROM t1 }
-    set memused2 [lindex [sqlite3_status SQLITE_STATUS_MEMORY_USED 0] 1]
-    expr {($memused2 + 2048 < $memused) || $pgovfl==0}
+    set after [db one {PRAGMA page_count}]
+    expr {$before>$after}
  } {1}
 }

@@ -75,6 +75,7 @@ set xtra_size 290
 db close
 sqlite3_shutdown
 sqlite3_config_lookaside 0 0
+sqlite3_config_pagecache 0 0
 sqlite3_initialize
 reset_highwater_marks
 build_test_db memsubsys1-1 {PRAGMA page_size=1024}
@@ -115,10 +116,10 @@ do_test memsubsys1-2.5 {
 db close
 sqlite3_shutdown
 sqlite3_config_pagecache [expr 512+$xtra_size] 20
+sqlite3_config singlethread
 sqlite3_initialize
 reset_highwater_marks
 build_test_db memsubsys1-3.1 {PRAGMA page_size=1024}
-#show_memstats
 do_test memsubsys1-3.1.3 {
  set pg_used [lindex [sqlite3_status SQLITE_STATUS_PAGECACHE_USED 0] 2]
 } 0
@@ -312,6 +313,7 @@ sqlite3_config_memstatus 1
 sqlite3_config_pagecache 0 0
 sqlite3_config_scratch 0 0
 sqlite3_config_lookaside 100 500
+sqlite3_config serialized
 sqlite3_initialize
 autoinstall_test_functions
 finish_test
@@ -24,6 +24,7 @@ do_test pcache2-1.1 {
  sqlite3_reset_auto_extension
  sqlite3_shutdown
  sqlite3_config_pagecache 6000 100
+  sqlite3_config singlethread
  sqlite3_initialize
  autoinstall_test_functions
  sqlite3_status SQLITE_STATUS_PAGECACHE_USED 1
@@ -73,6 +74,7 @@ catch {db2 close}
 sqlite3_reset_auto_extension
 sqlite3_shutdown
 sqlite3_config_pagecache 0 0
+sqlite3_config serialized
 sqlite3_initialize
 autoinstall_test_functions

@@ -1177,6 +1177,7 @@ int main(int argc, char **argv){
  int noSync = 0;               /* True for --nosync */
  int pageSize = 0;             /* Desired page size.  0 means default */
  int nPCache = 0, szPCache = 0;/* --pcache configuration */
+  int doPCache = 0;             /* True if --pcache is seen */
  int nScratch = 0, szScratch=0;/* --scratch configuration */
  int showStats = 0;            /* True for --stats */
  int nThread = 0;              /* --threads value */
@@ -1251,6 +1252,7 @@ int main(int argc, char **argv){
        if( i>=argc-2 ) fatal_error("missing arguments on %s\n", argv[i]);
        nPCache = integerValue(argv[i+1]);
        szPCache = integerValue(argv[i+2]);
+        doPCache = 1;
        i += 2;
      }else if( strcmp(z,"primarykey")==0 ){
        g.zPK = "PRIMARY KEY";
@@ -1317,10 +1319,12 @@ int main(int argc, char **argv){
    rc = sqlite3_config(SQLITE_CONFIG_HEAP, pHeap, nHeap, mnHeap);
    if( rc ) fatal_error("heap configuration failed: %d\n", rc);
  }
-  if( nPCache>0 && szPCache>0 ){
-    pPCache = malloc( nPCache*(sqlite3_int64)szPCache );
-    if( pPCache==0 ) fatal_error("cannot allocate %lld-byte pcache\n",
-                                 nPCache*(sqlite3_int64)szPCache);
+  if( doPCache ){
+    if( nPCache>0 && szPCache>0 ){
+      pPCache = malloc( nPCache*(sqlite3_int64)szPCache );
+      if( pPCache==0 ) fatal_error("cannot allocate %lld-byte pcache\n",
+                                   nPCache*(sqlite3_int64)szPCache);
+    }
    rc = sqlite3_config(SQLITE_CONFIG_PAGECACHE, pPCache, szPCache, nPCache);
    if( rc ) fatal_error("pcache configuration failed: %d\n", rc);
  }