diff --git a/manifest b/manifest
index f5a2a077ef..4988aa8489 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Minor\sperformance\soptimization\sin\spcache1.c.
-D 2015-06-12T13:04:51.385
+C Omit\smutex\scalls\sin\spcache1\swhen\sthe\smutex\sis\sNULL,\sfor\sa\ssignificant\nperformance\simprovement.
+D 2015-06-13T11:19:47.811
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 1063c58075b7400d93326b0eb332b48a54f53025
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -242,7 +242,7 @@ F src/pager.h c3476e7c89cdf1c6914e50a11f3714e30b4e0a77
 F src/parse.y 6d60dda8f8d418b6dc034f1fbccd816c459983a8
 F src/pcache.c 10539fb959849ad6efff80050541cab3d25089d4
 F src/pcache.h b44658c9c932d203510279439d891a2a83e12ba8
-F src/pcache1.c 0f2c218d9fa84814403033319036d8e9ecb06dfd
+F src/pcache1.c 7ca0caf7ec16c365aff3ddb4a7e00734a0e1fe97
 F src/pragma.c c1f4d012ea9f6b1ce52d341b2cd0ad72d560afd7
 F src/pragma.h b8632d7cdda7b25323fa580e3e558a4f0d4502cc
 F src/prepare.c 82e5db1013846a819f198336fed72c44c974e7b1
@@ -1286,7 +1286,8 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 711a176cbfad5dde6defa9648fba6d0d663af134
-R 9bc91229df1369aa902663b713f0e063
+P 2e8ad2ead9d146e312c693d9b967bbd5b92429d9 dcf4fb8d764611de60afea27cda0a8548ba7ca82
+R caec30587447e9722ed3cdf5357476d2
+T +closed dcf4fb8d764611de60afea27cda0a8548ba7ca82
 U drh
-Z c8fd78f00b5d9acfb5119a0b1df9ec4a
+Z d83dc113d9069d701eaef24905e6fe62
diff --git a/manifest.uuid b/manifest.uuid
index 6055917edd..aa300ff265 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-2e8ad2ead9d146e312c693d9b967bbd5b92429d9
\ No newline at end of file
+caf8f574e5c64da461c6dfba8a06cf3fb18aaa42
\ No newline at end of file
diff --git a/src/pcache1.c b/src/pcache1.c
index 5b1f3ba0df..685ec23e05 100644
--- a/src/pcache1.c
+++ b/src/pcache1.c
@@ -148,8 +148,15 @@ static SQLITE_WSD struct PCacheGlobal {
 /*
 ** Macros to enter and leave the PCache LRU mutex.
 */
-#define pcache1EnterMutex(X) sqlite3_mutex_enter((X)->mutex)
-#define pcache1LeaveMutex(X) sqlite3_mutex_leave((X)->mutex)
+#if !defined(SQLITE_ENABLE_MEMORY_MANAGEMENT) || SQLITE_THREADSAFE==0
+# define pcache1EnterMutex(X)  assert((X)->mutex==0)
+# define pcache1LeaveMutex(X)  assert((X)->mutex==0)
+# define PCACHE1_MIGHT_USE_GROUP_MUTEX 0
+#else
+# define pcache1EnterMutex(X) sqlite3_mutex_enter((X)->mutex)
+# define pcache1LeaveMutex(X) sqlite3_mutex_leave((X)->mutex)
+# define PCACHE1_MIGHT_USE_GROUP_MUTEX 1
+#endif
 
 /******************************************************************************/
 /******** Page Allocation/SQLITE_CONFIG_PCACHE Related Functions **************/
@@ -425,7 +432,7 @@ static void pcache1ResizeHash(PCache1 *p){
 **
 ** The PGroup mutex must be held when this function is called.
 */
-static void pcache1PinPage(PgHdr1 *pPage){
+static PgHdr1 *pcache1PinPage(PgHdr1 *pPage){
   PCache1 *pCache;
 
   assert( pPage!=0 );
@@ -448,6 +455,7 @@ static void pcache1PinPage(PgHdr1 *pPage){
   pPage->pLruPrev = 0;
   pPage->isPinned = 1;
   pCache->nRecyclable--;
+  return pPage;
 }
 
 
@@ -528,10 +536,12 @@ static int pcache1Init(void *NotUsed){
   UNUSED_PARAMETER(NotUsed);
   assert( pcache1.isInit==0 );
   memset(&pcache1, 0, sizeof(pcache1));
+#if SQLITE_THREADSAFE
   if( sqlite3GlobalConfig.bCoreMutex ){
     pcache1.grp.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_LRU);
     pcache1.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_PMEM);
   }
+#endif
   pcache1.grp.mxPinned = 10;
   pcache1.isInit = 1;
   return SQLITE_OK;
@@ -803,8 +813,13 @@ static SQLITE_NOINLINE PgHdr1 *pcache1FetchStage2(
 **      proceed to step 5. 
 **
 **   5. Otherwise, allocate and return a new page buffer.
+**
+** There are two versions of this routine.  pcache1FetchWithMutex() is
+** the general case.  pcache1FetchNoMutex() is a faster implementation for
+** the common case where pGroup->mutex is NULL.  The pcache1Fetch() wrapper
+** invokes the appropriate routine.
 */
-static sqlite3_pcache_page *pcache1Fetch(
+static PgHdr1 *pcache1FetchNoMutex(
   sqlite3_pcache *p, 
   unsigned int iKey, 
   int createFlag
@@ -812,28 +827,63 @@ static sqlite3_pcache_page *pcache1Fetch(
   PCache1 *pCache = (PCache1 *)p;
   PgHdr1 *pPage = 0;
 
-  assert( offsetof(PgHdr1,page)==0 );
-  assert( pCache->bPurgeable || createFlag!=1 );
-  assert( pCache->bPurgeable || pCache->nMin==0 );
-  assert( pCache->bPurgeable==0 || pCache->nMin==10 );
-  assert( pCache->nMin==0 || pCache->bPurgeable );
-  assert( pCache->nHash>0 );
-  pcache1EnterMutex(pCache->pGroup);
-
   /* Step 1: Search the hash table for an existing entry. */
   pPage = pCache->apHash[iKey % pCache->nHash];
   while( pPage && pPage->iKey!=iKey ){ pPage = pPage->pNext; }
 
   /* Step 2: Abort if no existing page is found and createFlag is 0 */
   if( pPage ){
-    if( !pPage->isPinned ) pcache1PinPage(pPage);
+    if( !pPage->isPinned ){
+      return pcache1PinPage(pPage);
+    }else{
+      return pPage;
+    }
   }else if( createFlag ){
     /* Steps 3, 4, and 5 implemented by this subroutine */
-    pPage = pcache1FetchStage2(pCache, iKey, createFlag);
+    return pcache1FetchStage2(pCache, iKey, createFlag);
+  }else{
+    return 0;
   }
+}
+#if PCACHE1_MIGHT_USE_GROUP_MUTEX
+static PgHdr1 *pcache1FetchWithMutex(
+  sqlite3_pcache *p, 
+  unsigned int iKey, 
+  int createFlag
+){
+  PCache1 *pCache = (PCache1 *)p;
+  PgHdr1 *pPage;
+
+  pcache1EnterMutex(pCache->pGroup);
+  pPage = pcache1FetchNoMutex(p, iKey, createFlag);
   assert( pPage==0 || pCache->iMaxKey>=iKey );
   pcache1LeaveMutex(pCache->pGroup);
-  return (sqlite3_pcache_page*)pPage;
+  return pPage;
+}
+#endif
+static sqlite3_pcache_page *pcache1Fetch(
+  sqlite3_pcache *p, 
+  unsigned int iKey, 
+  int createFlag
+){
+#if PCACHE1_MIGHT_USE_GROUP_MUTEX || defined(SQLITE_DEBUG)
+  PCache1 *pCache = (PCache1 *)p;
+#endif
+
+  assert( offsetof(PgHdr1,page)==0 );
+  assert( pCache->bPurgeable || createFlag!=1 );
+  assert( pCache->bPurgeable || pCache->nMin==0 );
+  assert( pCache->bPurgeable==0 || pCache->nMin==10 );
+  assert( pCache->nMin==0 || pCache->bPurgeable );
+  assert( pCache->nHash>0 );
+#if PCACHE1_MIGHT_USE_GROUP_MUTEX
+  if( pCache->pGroup->mutex ){
+    return (sqlite3_pcache_page*)pcache1FetchWithMutex(p, iKey, createFlag);
+  }else
+#endif
+  {
+    return (sqlite3_pcache_page*)pcache1FetchNoMutex(p, iKey, createFlag);
+  }
 }