From 982215a2c5b6bd5f121ef5d763decf42fdd45bd3 Mon Sep 17 00:00:00 2001
From: drh <drh@noemail.net>
Date: Sat, 13 Jun 2015 11:10:55 +0000
Subject: [PATCH] Avoid unnecessary mutex usage in pcache1, for a significant
 speedup.

FossilOrigin-Name: dcf4fb8d764611de60afea27cda0a8548ba7ca82
---
 manifest      | 15 ++++++---------
 manifest.uuid |  2 +-
 src/pcache1.c | 22 +++++++++++++++++++---
 3 files changed, 26 insertions(+), 13 deletions(-)

diff --git a/manifest b/manifest
index df814d0093..2f261b5b12 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Add\sa\sfast-path\simplementation\sof\spcache1Fetch()\sfor\sthe\scommon\scase\sof\nseparate\scaches\sthat\sdo\snot\suse\sa\smutex.
-D 2015-06-12T13:49:26.780
+C Avoid\sunnecessary\smutex\susage\sin\spcache1,\sfor\sa\ssignificant\sspeedup.
+D 2015-06-13T11:10:55.570
 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 0324126d981c6db4ba39e0a6b2bf79b690d3107f
+F src/pcache1.c 7ca0caf7ec16c365aff3ddb4a7e00734a0e1fe97
 F src/pragma.c c1f4d012ea9f6b1ce52d341b2cd0ad72d560afd7
 F src/pragma.h b8632d7cdda7b25323fa580e3e558a4f0d4502cc
 F src/prepare.c 82e5db1013846a819f198336fed72c44c974e7b1
@@ -1286,10 +1286,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 2e8ad2ead9d146e312c693d9b967bbd5b92429d9
-R 911300e4b1697824e69cfe439e19a5f8
-T *branch * faster-pcache1-fetch
-T *sym-faster-pcache1-fetch *
-T -sym-trunk *
+P 760700edb3ff1f5d6bf3058f874cc8e2808905c7
+R caec30587447e9722ed3cdf5357476d2
 U drh
-Z e8ae5ddb4580a5169c907c35e69dd177
+Z 153683ea51b205873f976242b39879f7
diff --git a/manifest.uuid b/manifest.uuid
index 859267d458..3e458c2d08 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-760700edb3ff1f5d6bf3058f874cc8e2808905c7
\ No newline at end of file
+dcf4fb8d764611de60afea27cda0a8548ba7ca82
\ No newline at end of file
diff --git a/src/pcache1.c b/src/pcache1.c
index 0a6d6d01d3..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 **************/
@@ -529,10 +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;
@@ -836,6 +845,7 @@ static PgHdr1 *pcache1FetchNoMutex(
     return 0;
   }
 }
+#if PCACHE1_MIGHT_USE_GROUP_MUTEX
 static PgHdr1 *pcache1FetchWithMutex(
   sqlite3_pcache *p, 
   unsigned int iKey, 
@@ -850,12 +860,15 @@ static PgHdr1 *pcache1FetchWithMutex(
   pcache1LeaveMutex(pCache->pGroup);
   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 );
@@ -863,9 +876,12 @@ static sqlite3_pcache_page *pcache1Fetch(
   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{
+  }else
+#endif
+  {
     return (sqlite3_pcache_page*)pcache1FetchNoMutex(p, iKey, createFlag);
   }
 }