A negative value N for the cache_size pragma adjusts the number of cache

pages to use approximately N kibibytes of memory.

FossilOrigin-Name: b3faa680aedc94ed8aa2819228c0d304b181cc51

manifest

@@ -1,5 +1,5 @@
-C For\sthe\smem1.c\ssystem\smalloc\simplementation,\suse\sthe\smalloc_usable_size()\nfunction\sif\sthe\sHAVE_MALLOC_USABLE_SIZE\smacro\sis\sdefined.\s\sUpdate\sautoconf\nto\slook\sfor\sthat\sfunction\swhen\sconfiguring.
-D 2011-11-09T01:53:25.593
+C A\snegative\svalue\sN\sfor\sthe\scache_size\spragma\sadjusts\sthe\snumber\sof\scache\npages\sto\suse\sapproximately\sN\skibibytes\sof\smemory.
+D 2011-11-09T14:23:04.394
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 5b4a3e12a850b021547e43daf886b25133b44c07
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -171,10 +171,10 @@ F src/os_win.c 49d418916428a59d773f39993db0ecde56ab4c37
 F src/pager.c db33d4bf1e3e019c34c220971cc6c3aa07c30f54
 F src/pager.h 9f81b08efb06db4ba8be69446e10b005c351373d
 F src/parse.y 12b7ebd61ea54f0e1b1083ff69cc2c8ce9353d58
-F src/pcache.c 8820564f6e32842190f06df545d964a5491ddae4
+F src/pcache.c b9d52e9f844d91c27c161279234f273fc02abc71
 F src/pcache.h c770382f9fae4ca5025c5523bd0aa13cd6ddc6f8
 F src/pcache1.c 9a42ace8022b3d38175c3b41802aa9bccd9c6a3a
-F src/pragma.c da8ef96b3eec351e81e0061c39810e548bcc96d7
+F src/pragma.c c5ba7627fbdedc02c7b8f52e77a3bceb030cf5ed
 F src/prepare.c e64261559a3187698a3e7e6c8b001a4f4f98dab4
 F src/printf.c 03104cbff6959ff45df69dc9060ba6212f60a869
 F src/random.c cd4a67b3953b88019f8cd4ccd81394a8ddfaba50
@@ -627,7 +627,7 @@ F test/pagesize.test 1dd51367e752e742f58e861e65ed7390603827a0
 F test/pcache.test 065aa286e722ab24f2e51792c1f093bf60656b16
 F test/pcache2.test a83efe2dec0d392f814bfc998def1d1833942025
 F test/permutations.test 522823b47238cb1754198f80817fe9f9158ede55
-F test/pragma.test 1ea0c85be853135bb7468e6eed48ee12b04794d4
+F test/pragma.test 7fa35e53085812dac94c2bfcbb02c2a4ad35df5e
 F test/pragma2.test 3a55f82b954242c642f8342b17dffc8b47472947
 F test/printf.test ec9870c4dce8686a37818e0bf1aba6e6a1863552
 F test/progress.test 5b075c3c790c7b2a61419bc199db87aaf48b8301
@@ -974,7 +974,7 @@ F tool/tostr.awk e75472c2f98dd76e06b8c9c1367f4ab07e122d06
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
 F tool/warnings-clang.sh 9f406d66e750e8ac031c63a9ef3248aaa347ef2a
 F tool/warnings.sh fbc018d67fd7395f440c28f33ef0f94420226381
-P 4da7095683ec821414e255419d63a24dbd9d726d
-R c213b277008496abb081e494c07b96f8
+P 2e8ab3cedfebc33a831837792b523d1aa7cdc6b7
+R f79cb2e5e3c648503ef136bcf9a7e813
 U drh
-Z adde38f0bee72bcf55d83cbeb4f89a8f
+Z ee913c4e43d90078be9388d453dfd115

manifest.uuid

@@ -1 +1 @@
-2e8ab3cedfebc33a831837792b523d1aa7cdc6b7
+b3faa680aedc94ed8aa2819228c0d304b181cc51

src/pcache.c

@@ -20,7 +20,7 @@ struct PCache {
   PgHdr *pDirty, *pDirtyTail;         /* List of dirty pages in LRU order */
   PgHdr *pSynced;                     /* Last synced page in dirty page list */
   int nRef;                           /* Number of referenced pages */
-  int nMax;                           /* Configured cache size */
+  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 */
@@ -181,7 +181,7 @@ void sqlite3PcacheOpen(
   p->bPurgeable = bPurgeable;
   p->xStress = xStress;
   p->pStress = pStress;
-  p->nMax = 100;
+  p->szCache = 100;
 }
 
 /*
@@ -198,6 +198,17 @@ void sqlite3PcacheSetPageSize(PCache *pCache, int szPage){
   pCache->szPage = szPage;
 }
 
+/*
+** Compute the number of pages of cache requested.
+*/
+static int numberOfCachePages(PCache *p){
+  if( p->szCache>=0 ){
+    return p->szCache;
+  }else{
+    return (-1024*p->szCache)/(p->szPage+p->szExtra);
+  }
+}
+
 /*
 ** Try to obtain a page from the cache.
 */
@@ -226,7 +237,7 @@ int sqlite3PcacheFetch(
     if( !p ){
       return SQLITE_NOMEM;
     }
-    sqlite3GlobalConfig.pcache2.xCachesize(p, pCache->nMax);
+    sqlite3GlobalConfig.pcache2.xCachesize(p, numberOfCachePages(pCache));
     pCache->pCache = p;
   }
 
@@ -259,7 +270,7 @@ int sqlite3PcacheFetch(
                   "spill page %d making room for %d - cache used: %d/%d",
                   pPg->pgno, pgno,
                   sqlite3GlobalConfig.pcache.xPagecount(pCache->pCache),
-                  pCache->nMax);
+                  numberOfCachePages(pCache));
 #endif
       rc = pCache->xStress(pCache->pStress, pPg);
       if( rc!=SQLITE_OK && rc!=SQLITE_BUSY ){
@@ -569,7 +580,7 @@ int sqlite3PcachePagecount(PCache *pCache){
 ** Get the suggested cache-size value.
 */
 int sqlite3PcacheGetCachesize(PCache *pCache){
-  return pCache->nMax;
+  return numberOfCachePages(pCache);
 }
 #endif
 
@@ -577,9 +588,10 @@ int sqlite3PcacheGetCachesize(PCache *pCache){
 ** Set the suggested cache-size value.
 */
 void sqlite3PcacheSetCachesize(PCache *pCache, int mxPage){
-  pCache->nMax = mxPage;
+  pCache->szCache = mxPage;
   if( pCache->pCache ){
-    sqlite3GlobalConfig.pcache2.xCachesize(pCache->pCache, mxPage);
+    sqlite3GlobalConfig.pcache2.xCachesize(pCache->pCache,
+                                           numberOfCachePages(pCache));
   }
 }
 

src/pragma.c

@@ -684,14 +684,11 @@ void sqlite3Pragma(
   **  PRAGMA [database.]cache_size=N
   **
   ** The first form reports the current local setting for the
-  ** page cache size.  The local setting can be different from
-  ** the persistent cache size value that is stored in the database
-  ** file itself.  The value returned is the maximum number of
-  ** pages in the page cache.  The second form sets the local
-  ** page cache size value.  It does not change the persistent
-  ** cache size stored on the disk so the cache size will revert
-  ** to its default value when the database is closed and reopened.
-  ** N should be a positive integer.
+  ** page cache size. The second form sets the local
+  ** page cache size value.  If N is positive then that is the
+  ** number of pages in the cache.  If N is negative, then the
+  ** number of pages is adjusted so that the cache uses -N kibibytes
+  ** of memory.
   */
   if( sqlite3StrICmp(zLeft,"cache_size")==0 ){
     if( sqlite3ReadSchema(pParse) ) goto pragma_out;
@@ -699,7 +696,7 @@ void sqlite3Pragma(
     if( !zRight ){
       returnSingleInt(pParse, "cache_size", pDb->pSchema->cache_size);
     }else{
-      int size = sqlite3AbsInt32(sqlite3Atoi(zRight));
+      int size = sqlite3Atoi(zRight);
       pDb->pSchema->cache_size = size;
       sqlite3BtreeSetCacheSize(pDb->pBt, pDb->pSchema->cache_size);
     }

test/pragma.test

@@ -99,7 +99,7 @@ do_test pragma-1.5 {
     PRAGMA default_cache_size;
     PRAGMA synchronous;
   }
-} [list 4321 $DFLT_CACHE_SZ 0]
+} [list -4321 $DFLT_CACHE_SZ 0]
 do_test pragma-1.6 {
   execsql {
     PRAGMA synchronous=ON;
@@ -107,7 +107,7 @@ do_test pragma-1.6 {
     PRAGMA default_cache_size;
     PRAGMA synchronous;
   }
-} [list 4321 $DFLT_CACHE_SZ 1]
+} [list -4321 $DFLT_CACHE_SZ 1]
 do_test pragma-1.7 {
   db close
   sqlite3 db test.db