Index: src/pcache1.c
==================================================================
--- src/pcache1.c
+++ src/pcache1.c
@@ -146,12 +146,19 @@
 #define pcache1 (GLOBAL(struct PCacheGlobal, pcache1_g))
 
 /*
 ** 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 **************/
 
 /*
@@ -423,11 +430,11 @@
 ** PGroup LRU list, if is part of it. If pPage is not part of the PGroup
 ** LRU list, then this function is a no-op.
 **
 ** 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 );
   assert( pPage->isPinned==0 );
   pCache = pPage->pCache;
@@ -446,10 +453,11 @@
   }
   pPage->pLruNext = 0;
   pPage->pLruPrev = 0;
   pPage->isPinned = 1;
   pCache->nRecyclable--;
+  return pPage;
 }
 
 
 /*
 ** Remove the page supplied as an argument from the hash table 
@@ -526,14 +534,16 @@
 */
 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;
 }
 
@@ -801,41 +811,81 @@
 **      then attempt to recycle a page from the LRU list. If it is the right
 **      size, return the recycled buffer. Otherwise, free the buffer and
 **      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
 ){
   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);
+  }
 }
 
 
 /*
 ** Implementation of the sqlite3_pcache.xUnpin method.