Index: src/pcache1.c
==================================================================
--- src/pcache1.c
+++ src/pcache1.c
@@ -496,29 +496,59 @@
 */
 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( pCache->nPage==nPage );
+  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);
+  }
 }
 
 /******************************************************************************/
 /******** sqlite3_pcache Methods **********************************************/
 
@@ -943,11 +973,11 @@
 static void pcache1Destroy(sqlite3_pcache *p){
   PCache1 *pCache = (PCache1 *)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 );
   pGroup->nMinPage -= pCache->nMin;
   pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage;

Index: src/sqliteInt.h
==================================================================
--- src/sqliteInt.h
+++ src/sqliteInt.h
@@ -197,11 +197,11 @@
 ** It determines whether or not the features related to 
 ** SQLITE_CONFIG_MEMSTATUS are available by default or not. This value can
 ** 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
 
 /*
 ** Exactly one of the following macros must be defined in order to
 ** specify which memory allocation subsystem to use.
@@ -3812,7 +3812,28 @@
 */
 #if SQLITE_MAX_WORKER_THREADS>0
 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_ */