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Refactor the sqlite3PcacheFetch() routine into three separate routines,

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which are significantly faster overall and about 100 bytes smaller in
size as well.

FossilOrigin-Name: bdb6e4978d1a26d5f795262172605184264ede9c
This commit is contained in:
drh
2014-08-27 23:18:01 +00:00
parent a1dc42aa91
commit bc59ac0e26
5 changed files with 155 additions and 80 deletions
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191
src/pcache.c
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@@ -231,15 +231,33 @@ int sqlite3PcacheSetPageSize(PCache *pCache, int szPage){
/*
** Try to obtain a page from the cache.
**
** This routine returns a pointer to an sqlite3_pcache_page object if
** such an object is already in cache, or if a new one is created.
** This routine returns a NULL pointer if the object was not in cache
** and could not be created.
**
** The createFlags should be 0 to check for existing pages and should
** be 3 (not 1, but 3) to try to create a new page.
**
** If the createFlag is 0, then NULL is always returned if the page
** is not already in the cache. If createFlag is 1, then a new page
** is created only if that can be done without spilling dirty pages
** and without exceeding the cache size limit.
**
** The caller needs to invoke sqlite3PcacheFetchFinish() to properly
** initialize the sqlite3_pcache_page object and convert it into a
** PgHdr object. The sqlite3PcacheFetch() and sqlite3PcacheFetchFinish()
** routines are split this way for performance reasons. When separated
** they can both (usually) operate without having to push values to
** the stack on entry and pop them back off on exit, which saves a
** lot of pushing and popping.
*/
int sqlite3PcacheFetch(
sqlite3_pcache_page *sqlite3PcacheFetch(
PCache *pCache, /* Obtain the page from this cache */
Pgno pgno, /* Page number to obtain */
int createFlag, /* If true, create page if it does not exist already */
PgHdr **ppPage /* Write the page here */
int createFlag /* If true, create page if it does not exist already */
){
sqlite3_pcache_page *pPage;
PgHdr *pPgHdr = 0;
int eCreate;
assert( pCache!=0 );
@@ -258,69 +276,116 @@ int sqlite3PcacheFetch(
assert( eCreate==0 || eCreate==1 || eCreate==2 );
assert( createFlag==0 || pCache->eCreate==eCreate );
assert( createFlag==0 || eCreate==1+(!pCache->bPurgeable||!pCache->pDirty) );
pPage = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, eCreate);
if( !pPage && eCreate==1 ){
PgHdr *pPg;
return sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, eCreate);
}
/* Find a dirty page to write-out and recycle. First try to find a
** page that does not require a journal-sync (one with PGHDR_NEED_SYNC
** cleared), but if that is not possible settle for any other
** unreferenced dirty page.
*/
expensive_assert( pcacheCheckSynced(pCache) );
for(pPg=pCache->pSynced;
pPg && (pPg->nRef || (pPg->flags&PGHDR_NEED_SYNC));
pPg=pPg->pDirtyPrev
);
pCache->pSynced = pPg;
if( !pPg ){
for(pPg=pCache->pDirtyTail; pPg && pPg->nRef; pPg=pPg->pDirtyPrev);
}
if( pPg ){
int rc;
/*
** If the sqlite3PcacheFetch() routine is unable to allocate a new
** page because new clean pages are available for reuse and the cache
** size limit has been reached, then this routine can be invoked to
** try harder to allocate a page. This routine might invoke the stress
** callback to spill dirty pages to the journal. It will then try to
** allocate the new page and will only fail to allocate a new page on
** an OOM error.
**
** This routine should be invoked only after sqlite3PcacheFetch() fails.
*/
int sqlite3PcacheFetchStress(
PCache *pCache, /* Obtain the page from this cache */
Pgno pgno, /* Page number to obtain */
sqlite3_pcache_page **ppPage /* Write result here */
){
PgHdr *pPg;
if( pCache->eCreate==2 ) return 0;
/* Find a dirty page to write-out and recycle. First try to find a
** page that does not require a journal-sync (one with PGHDR_NEED_SYNC
** cleared), but if that is not possible settle for any other
** unreferenced dirty page.
*/
expensive_assert( pcacheCheckSynced(pCache) );
for(pPg=pCache->pSynced;
pPg && (pPg->nRef || (pPg->flags&PGHDR_NEED_SYNC));
pPg=pPg->pDirtyPrev
);
pCache->pSynced = pPg;
if( !pPg ){
for(pPg=pCache->pDirtyTail; pPg && pPg->nRef; pPg=pPg->pDirtyPrev);
}
if( pPg ){
int rc;
#ifdef SQLITE_LOG_CACHE_SPILL
sqlite3_log(SQLITE_FULL,
"spill page %d making room for %d - cache used: %d/%d",
pPg->pgno, pgno,
sqlite3GlobalConfig.pcache.xPagecount(pCache->pCache),
numberOfCachePages(pCache));
sqlite3_log(SQLITE_FULL,
"spill page %d making room for %d - cache used: %d/%d",
pPg->pgno, pgno,
sqlite3GlobalConfig.pcache.xPagecount(pCache->pCache),
numberOfCachePages(pCache));
#endif
rc = pCache->xStress(pCache->pStress, pPg);
if( rc!=SQLITE_OK && rc!=SQLITE_BUSY ){
return rc;
}
}
pPage = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, 2);
}
if( pPage ){
pPgHdr = (PgHdr *)pPage->pExtra;
if( !pPgHdr->pPage ){
memset(pPgHdr, 0, sizeof(PgHdr));
pPgHdr->pPage = pPage;
pPgHdr->pData = pPage->pBuf;
pPgHdr->pExtra = (void *)&pPgHdr[1];
memset(pPgHdr->pExtra, 0, pCache->szExtra);
pPgHdr->pCache = pCache;
pPgHdr->pgno = pgno;
}
assert( pPgHdr->pCache==pCache );
assert( pPgHdr->pgno==pgno );
assert( pPgHdr->pData==pPage->pBuf );
assert( pPgHdr->pExtra==(void *)&pPgHdr[1] );
if( 0==pPgHdr->nRef ){
pCache->nRef++;
}
pPgHdr->nRef++;
if( pgno==1 ){
pCache->pPage1 = pPgHdr;
rc = pCache->xStress(pCache->pStress, pPg);
if( rc!=SQLITE_OK && rc!=SQLITE_BUSY ){
return rc;
}
}
*ppPage = pPgHdr;
return (pPgHdr==0 && eCreate) ? SQLITE_NOMEM : SQLITE_OK;
*ppPage = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, 2);
return *ppPage==0 ? SQLITE_NOMEM : SQLITE_OK;
}
/*
** This is a helper routine for sqlite3PcacheFetchFinish()
**
** In the uncommon case where the page being fetched has not been
** initialized, this routine is invoked to do the initialization.
** This routine is broken out into a separate function since it
** requires extra stack manipulation that can be avoided in the common
** case.
*/
static SQLITE_NOINLINE PgHdr *pcacheFetchFinishWithInit(
PCache *pCache, /* Obtain the page from this cache */
Pgno pgno, /* Page number obtained */
sqlite3_pcache_page *pPage /* Page obtained by prior PcacheFetch() call */
){
PgHdr *pPgHdr;
assert( pPage!=0 );
pPgHdr = (PgHdr*)pPage->pExtra;
assert( pPgHdr->pPage==0 );
memset(pPgHdr, 0, sizeof(PgHdr));
pPgHdr->pPage = pPage;
pPgHdr->pData = pPage->pBuf;
pPgHdr->pExtra = (void *)&pPgHdr[1];
memset(pPgHdr->pExtra, 0, pCache->szExtra);
pPgHdr->pCache = pCache;
pPgHdr->pgno = pgno;
return sqlite3PcacheFetchFinish(pCache,pgno,pPage);
}
/*
** This routine converts the sqlite3_pcache_page object returned by
** sqlite3PcacheFetch() into an initialized PgHdr object. This routine
** must be called after sqlite3PcacheFetch() in order to get a usable
** result.
*/
PgHdr *sqlite3PcacheFetchFinish(
PCache *pCache, /* Obtain the page from this cache */
Pgno pgno, /* Page number obtained */
sqlite3_pcache_page *pPage /* Page obtained by prior PcacheFetch() call */
){
PgHdr *pPgHdr;
if( pPage==0 ) return 0;
pPgHdr = (PgHdr *)pPage->pExtra;
if( !pPgHdr->pPage ){
return pcacheFetchFinishWithInit(pCache, pgno, pPage);
}
if( 0==pPgHdr->nRef ){
pCache->nRef++;
}
pPgHdr->nRef++;
if( pgno==1 ){
pCache->pPage1 = pPgHdr;
}
return pPgHdr;
}
/*