Try to make pcache1TruncateUnsafe() run faster for the case where iLimit is

very close to iMaxKey.

FossilOrigin-Name: 9ab53605d562a926c5620cba9dc96a3b812a432f

manifest

@@ -1,5 +1,5 @@
-C Optimizations\saimed\sat\sreducing\sthe\snumber\sof\smemcpy()\soperations\srequired\sby\sbalance_nonroot().
-D 2014-10-27T14:26:54.508
+C Try\sto\smake\spcache1TruncateUnsafe()\srun\sfaster\sfor\sthe\scase\swhere\siLimit\sis\nvery\sclose\sto\siMaxKey.
+D 2016-08-10T03:35:50.389
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in cf57f673d77606ab0f2d9627ca52a9ba1464146a
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -172,7 +172,7 @@ F src/auth.c d8abcde53426275dab6243b441256fcd8ccbebb2
 F src/backup.c a31809c65623cc41849b94d368917f8bb66e6a7e
 F src/bitvec.c 19a4ba637bd85f8f63fc8c9bae5ade9fb05ec1cb
 F src/btmutex.c 49ca66250c7dfa844a4d4cb8272b87420d27d3a5
-F src/btree.c 9790fb4df51d36861bcbb8cd0a9b41586cbae699
+F src/btree.c 44c34502f17681eb957149cc1b8b4e1964ed231a
 F src/btree.h a79aa6a71e7f1055f01052b7f821bd1c2dce95c8
 F src/btreeInt.h 026d0129724e8f265fdc60d44ec240cf5a4e6179
 F src/build.c 9dc2bd94347b878c89627000c92b0c8d97ec2919
@@ -220,7 +220,7 @@ F src/pager.h d1eee3c3f741be247ce6d82752a178515fc8578b
 F src/parse.y 5dfead8aed90cb0c7c1115898ee2266804daff45
 F src/pcache.c 4121a0571c18581ee9f82f086d5e2030051ebd6a
 F src/pcache.h 9b559127b83f84ff76d735c8262f04853be0c59a
-F src/pcache1.c e412cb585f777c840ddce0500eddc5c6043c2bb5
+F src/pcache1.c 04279e6cf595ba3520707886e1f4e3a0b6312cad
 F src/pragma.c 3f3e959390a10c0131676f0e307acce372777e0f
 F src/prepare.c 6ef0cf2f9274982988ed6b7cab1be23147e94196
 F src/printf.c 090fac0f779c93c8a95089a125339686648835e4
@@ -232,7 +232,7 @@ F src/shell.c 282f8f5278e0c78eb442217531172ec9e1538796
 F src/sqlite.h.in 4a5e5158c189d2bcd45c7c4607c2c0eb6d25c153
 F src/sqlite3.rc 992c9f5fb8285ae285d6be28240a7e8d3a7f2bad
 F src/sqlite3ext.h 17d487c3c91b0b8c584a32fbeb393f6f795eea7d
-F src/sqliteInt.h 90519c3b3e8ee90adfce013234c4bd07275d77b5
+F src/sqliteInt.h c5d6a3bd2f2514ed08e3b842201b211ad3795d25
 F src/sqliteLimit.h 164b0e6749d31e0daa1a4589a169d31c0dec7b3d
 F src/status.c 961d5926e5a8fda611d385ec22c226b8635cd1cb
 F src/table.c 2e99ef7ef16187e17033d9398dc962ce22dab5cb
@@ -1207,7 +1207,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P fc6920b5483eeeb06a474ff399a21afa51dc4859 1f80f8c136ac970dcc7fb2337263dc5922e348c3
-R ed2304a6a2e587056109284e9717f063
-U dan
-Z 986c15e36469a97fa56839a4b2a55b25
+P 5980e625dbb694dc3b0535e71fd986a6d211e245
+R 2aecde0e663e22b28208114fb4e83a67
+U drh
+Z 9f57a23eafe4610b0bd9a6ac18d687c6

manifest.uuid

@@ -1 +1 @@
-face33bea1ba3a6d57780655fa827226b4d2baa9
+9ab53605d562a926c5620cba9dc96a3b812a432f

src/btree.c

@@ -6786,7 +6786,7 @@ static int balance_nonroot(
     assert( d<nMaxCells );
     assert( r<nMaxCells );
     while( szRight==0 
-       || (!bBulk && szRight+szCell[d]+2<=szLeft-(szCell[r]+2)) 
+       || (!bBulk && szRight+szCell[d]+2<=szLeft-(szCell[r]+(i==k-1?0:2))) 
     ){
       szRight += szCell[d] + 2;
       szLeft -= szCell[r] + 2;

src/pcache1.c

@@ -498,25 +498,55 @@ static void pcache1TruncateUnsafe(
   PCache1 *pCache,             /* The cache to truncate */
   unsigned int iLimit          /* Drop pages with this pgno or larger */
 ){
-  TESTONLY( unsigned int nPage = 0; )  /* To assert pCache->nPage is correct */
-  unsigned int h;
+  TESTONLY( int nPage = 0; )  /* To assert pCache->nPage is correct */
+  unsigned int h, iStop;
+  START_DEBUG_TIMER;
+  int nFree = 0;
   assert( sqlite3_mutex_held(pCache->pGroup->mutex) );
-  for(h=0; h<pCache->nHash; h++){
-    PgHdr1 **pp = &pCache->apHash[h]; 
+  assert( pCache->iMaxKey >= iLimit );
+  assert( pCache->nHash > 0 );
+  if( pCache->iMaxKey - iLimit < pCache->nHash/2 ){
+    /* If we are just shaving the last few pages off the end of the
+    ** cache, then there is no point in scanning the entire hash table.
+    ** Only scan those hash slots that might contain pages that need to
+    ** be removed. */
+    iStop = iLimit % pCache->nHash;
+    h = pCache->iMaxKey % pCache->nHash;
+    TESTONLY( nPage = -10; )  /* Disable the pCache->nPage validity check */
+  }else{
+    /* This is the general case where many pages are being removed.
+    ** It is necessary to scan the entire hash table */
+    iStop = 0;
+    h = pCache->nHash - 1;
+  }
+  for(;;){
+    PgHdr1 **pp;
     PgHdr1 *pPage;
+    assert( h<pCache->nHash );
+    pp = &pCache->apHash[h]; 
     while( (pPage = *pp)!=0 ){
       if( pPage->iKey>=iLimit ){
         pCache->nPage--;
+        nFree++;
         *pp = pPage->pNext;
         if( !pPage->isPinned ) pcache1PinPage(pPage);
         pcache1FreePage(pPage);
       }else{
         pp = &pPage->pNext;
-        TESTONLY( nPage++; )
+        TESTONLY( if( nPage>=0 ) nPage++; )
       }
     }
+    if( h==iStop ) break;
+    h = h ? h-1 : pCache->nHash - 1;
+  }
+  assert( nPage<0 || pCache->nPage==(unsigned)nPage );
+  END_DEBUG_TIMER( DEBUG_TIMER_BIG_TIMEOUT ){
+    sqlite3_log(SQLITE_NOTICE, 
+       "slow pcache1TruncateUnsafe() %lld "
+       " nFree=%d nHash=%d nPage=%d iLimit=%d iMaxKey=%d",
+       iDebugTimer,
+       nFree, pCache->nHash, pCache->nPage, iLimit, pCache->iMaxKey);
   }
-  assert( pCache->nPage==nPage );
 }
 
 /******************************************************************************/
@@ -945,7 +975,7 @@ static void pcache1Destroy(sqlite3_pcache *p){
   PGroup *pGroup = pCache->pGroup;
   assert( pCache->bPurgeable || (pCache->nMax==0 && pCache->nMin==0) );
   pcache1EnterMutex(pGroup);
-  pcache1TruncateUnsafe(pCache, 0);
+  if( pCache->nPage ) pcache1TruncateUnsafe(pCache, 0);
   assert( pGroup->nMaxPage >= pCache->nMax );
   pGroup->nMaxPage -= pCache->nMax;
   assert( pGroup->nMinPage >= pCache->nMin );

src/sqliteInt.h

@@ -199,7 +199,7 @@
 ** be overridden at runtime using the sqlite3_config() API.
 */
 #if !defined(SQLITE_DEFAULT_MEMSTATUS)
-# define SQLITE_DEFAULT_MEMSTATUS 1
+# define SQLITE_DEFAULT_MEMSTATUS 0
 #endif
 
 /*
@@ -3815,4 +3815,25 @@ int sqlite3ThreadCreate(SQLiteThread**,void*(*)(void*),void*);
 int sqlite3ThreadJoin(SQLiteThread*, void**);
 #endif
 
+#include <sys/time.h>
+#define START_DEBUG_TIMER \
+  sqlite3_uint64 iDebugTimerStart, iDebugTimer;                     \
+  struct timeval debug_timer_var;                                   \
+  gettimeofday(&debug_timer_var, 0);                                \
+  iDebugTimerStart = 1000000*(sqlite3_uint64)debug_timer_var.tv_sec \
+                     + debug_timer_var.tv_usec;
+
+#define END_DEBUG_TIMER(nDebugUsec) \
+  gettimeofday(&debug_timer_var, 0);                                \
+  iDebugTimer = 1000000*(sqlite3_uint64)debug_timer_var.tv_sec      \
+                +debug_timer_var.tv_usec-iDebugTimerStart;          \
+  if( iDebugTimer>=nDebugUsec )
+
+#ifndef DEBUG_TIMER_BIG_TIMEOUT
+# define DEBUG_TIMER_BIG_TIMEOUT  10000
+#endif
+#ifndef DEBUG_TIMER_SMALL_TIMEOUT
+# define DEBUG_TIMER_SMALL_TIMEOUT 1000
+#endif
+
 #endif /* _SQLITEINT_H_ */