From fe21a796f7af89c7bf6c588f28a2a2d3f646218f Mon Sep 17 00:00:00 2001
From: drh <drh@noemail.net>
Date: Mon, 3 Feb 2014 17:04:29 +0000
Subject: [PATCH] Performance optimizations in sqlite3PcacheFetch().

FossilOrigin-Name: b60cc11ef775c23a2245d9e7a00dab34013f3ccb
---
 manifest      | 13 ++++++-------
 manifest.uuid |  2 +-
 src/pcache.c  | 34 ++++++++++++++++++++++++++--------
 3 files changed, 33 insertions(+), 16 deletions(-)

diff --git a/manifest b/manifest
index 90c123fd33..8ed9435be8 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Provide\shints\sto\sthe\sbtree\slayer\sNext\sand\sPrevious\sprimitives\sto\slet\sthem\s\nknow\sif\sthey\scan\sbe\sno-ops\sif\sthe\sunderlying\sindex\sis\sunique.
-D 2014-02-03T14:04:11.993
+C Performance\soptimizations\sin\ssqlite3PcacheFetch().
+D 2014-02-03T17:04:29.099
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 2ef13430cd359f7b361bb863504e227b25cc7f81
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -210,7 +210,7 @@ F src/os_win.c 1b21af72c5fa6f9e519a5fcab33e80d182b1aedb
 F src/pager.c efa923693e958696eee69b205a20bfbc402c8480
 F src/pager.h ffd5607f7b3e4590b415b007a4382f693334d428
 F src/parse.y bd51bc17cbfe7549adb4ca3747b1c3d384645065
-F src/pcache.c f8043b433a57aba85384a531e3937a804432a346
+F src/pcache.c d8eafac28290d4bb80332005435db44991d07fc2
 F src/pcache.h a5e4f5d9f5d592051d91212c5949517971ae6222
 F src/pcache1.c 102e6f5a2fbc646154463eb856d1fd716867b64c
 F src/pragma.c ed409ce4104cf4d9de6ead40ace70974f124853b
@@ -1152,8 +1152,7 @@ F tool/vdbe-compress.tcl 0cf56e9263a152b84da86e75a5c0cdcdb7a47891
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh d1a6de74685f360ab718efda6265994b99bbea01
 F tool/win/sqlite.vsix 030f3eeaf2cb811a3692ab9c14d021a75ce41fff
-P e816dd924619db5f766de6df74ea2194f3e3b538
-Q +a2c347faf91d82cf8734621bf378a6dd68b00957
-R be5a44c31c2829557525011b36aec00e
+P 6c643e45c274e755dc5a1a65673df79261c774be
+R 8b5419aed1d20751ed2fa03b47b5e0a6
 U drh
-Z 23965260487a528a52632de193207045
+Z f3fb6a665960323d1a0ee233aafe4773
diff --git a/manifest.uuid b/manifest.uuid
index 243bc6de49..bad810a1b8 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-6c643e45c274e755dc5a1a65673df79261c774be
\ No newline at end of file
+b60cc11ef775c23a2245d9e7a00dab34013f3ccb
\ No newline at end of file
diff --git a/src/pcache.c b/src/pcache.c
index 482a188bee..e18bf93be0 100644
--- a/src/pcache.c
+++ b/src/pcache.c
@@ -23,7 +23,8 @@ struct PCache {
   int szCache;                        /* Configured cache size */
   int szPage;                         /* Size of every page in this cache */
   int szExtra;                        /* Size of extra space for each page */
-  int bPurgeable;                     /* True if pages are on backing store */
+  u8 bPurgeable;                      /* True if pages are on backing store */
+  u8 eCreate;                         /* eCreate value for for xFetch() */
   int (*xStress)(void*,PgHdr*);       /* Call to try make a page clean */
   void *pStress;                      /* Argument to xStress */
   sqlite3_pcache *pCache;             /* Pluggable cache module */
@@ -90,6 +91,10 @@ static void pcacheRemoveFromDirtyList(PgHdr *pPage){
   }else{
     assert( pPage==p->pDirty );
     p->pDirty = pPage->pDirtyNext;
+    if( p->pDirty==0 && p->bPurgeable ){
+      assert( p->eCreate==1 );
+      p->eCreate = 2;
+    }
   }
   pPage->pDirtyNext = 0;
   pPage->pDirtyPrev = 0;
@@ -110,6 +115,9 @@ static void pcacheAddToDirtyList(PgHdr *pPage){
   if( pPage->pDirtyNext ){
     assert( pPage->pDirtyNext->pDirtyPrev==0 );
     pPage->pDirtyNext->pDirtyPrev = pPage;
+  }else if( p->bPurgeable ){
+    assert( p->eCreate==2 );
+    p->eCreate = 1;
   }
   p->pDirty = pPage;
   if( !p->pDirtyTail ){
@@ -179,6 +187,7 @@ void sqlite3PcacheOpen(
   p->szPage = szPage;
   p->szExtra = szExtra;
   p->bPurgeable = bPurgeable;
+  p->eCreate = 2;
   p->xStress = xStress;
   p->pStress = pStress;
   p->szCache = 100;
@@ -218,7 +227,7 @@ int sqlite3PcacheFetch(
   int createFlag,       /* If true, create page if it does not exist already */
   PgHdr **ppPage        /* Write the page here */
 ){
-  sqlite3_pcache_page *pPage = 0;
+  sqlite3_pcache_page *pPage;
   PgHdr *pPgHdr = 0;
   int eCreate;
 
@@ -229,8 +238,12 @@ int sqlite3PcacheFetch(
   /* If the pluggable cache (sqlite3_pcache*) has not been allocated,
   ** allocate it now.
   */
-  if( !pCache->pCache && createFlag ){
+  if( !pCache->pCache ){
     sqlite3_pcache *p;
+    if( !createFlag ){
+      *ppPage = 0;
+      return SQLITE_OK;
+    }
     p = sqlite3GlobalConfig.pcache2.xCreate(
         pCache->szPage, pCache->szExtra + sizeof(PgHdr), pCache->bPurgeable
     );
@@ -241,11 +254,16 @@ int sqlite3PcacheFetch(
     pCache->pCache = p;
   }
 
-  eCreate = createFlag * (1 + (!pCache->bPurgeable || !pCache->pDirty));
-  if( pCache->pCache ){
-    pPage = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, eCreate);
-  }
-
+  /* eCreate defines what to do if the page does not exist.
+  **    0     Do not allocate a new page.  (createFlag==0)
+  **    1     Allocate a new page if doing so is inexpensive.
+  **          (createFlag==1 AND bPurgeable AND pDirty)
+  **    2     Allocate a new page even it doing so is difficult.
+  **          (createFlag==1 AND !(bPurgeable AND pDirty)
+  */
+  eCreate = createFlag==0 ? 0 : pCache->eCreate;
+  assert( (createFlag*(1+(!pCache->bPurgeable||!pCache->pDirty)))==eCreate );
+  pPage = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, eCreate);
   if( !pPage && eCreate==1 ){
     PgHdr *pPg;