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

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pages to use approximately N kibibytes of memory.

FossilOrigin-Name: b3faa680aedc94ed8aa2819228c0d304b181cc51
This commit is contained in:
drh
2011-11-09 14:23:04 +00:00
parent 6a8ab6d9cb
commit 3b42abb35b
5 changed files with 36 additions and 27 deletions
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26
src/pcache.c
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@@ -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));
}
}