**
** The PCache mutex must be held when this function is called.
*/
-static int pcache1ResizeHash(PCache1 *p){
+static void pcache1ResizeHash(PCache1 *p){
PgHdr1 **apNew;
unsigned int nNew;
unsigned int i;
p->apHash = apNew;
p->nHash = nNew;
}
-
- return (p->apHash ? SQLITE_OK : SQLITE_NOMEM);
}
/*
memset(&pcache1, 0, sizeof(pcache1));
}
+/* forward declaration */
+static void pcache1Destroy(sqlite3_pcache *p);
+
/*
** Implementation of the sqlite3_pcache.xCreate method.
**
pCache->szPage = szPage;
pCache->szExtra = szExtra;
pCache->bPurgeable = (bPurgeable ? 1 : 0);
+ pcache1EnterMutex(pGroup);
+ pcache1ResizeHash(pCache);
if( bPurgeable ){
pCache->nMin = 10;
- pcache1EnterMutex(pGroup);
pGroup->nMinPage += pCache->nMin;
pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage;
- pcache1LeaveMutex(pGroup);
+ }
+ pcache1LeaveMutex(pGroup);
+ if( pCache->nHash==0 ){
+ pcache1Destroy((sqlite3_pcache*)pCache);
+ pCache = 0;
}
}
return (sqlite3_pcache *)pCache;
return n;
}
+
/*
-** Implementation of the sqlite3_pcache.xFetch method.
-**
-** Fetch a page by key value.
+** Implement steps 3, 4, and 5 of the pcache1Fetch() algorithm described
+** in the header of the pcache1Fetch() procedure.
**
-** Whether or not a new page may be allocated by this function depends on
-** the value of the createFlag argument. 0 means do not allocate a new
-** page. 1 means allocate a new page if space is easily available. 2
-** means to try really hard to allocate a new page.
-**
-** For a non-purgeable cache (a cache used as the storage for an in-memory
-** database) there is really no difference between createFlag 1 and 2. So
-** the calling function (pcache.c) will never have a createFlag of 1 on
-** a non-purgeable cache.
-**
-** There are three different approaches to obtaining space for a page,
-** depending on the value of parameter createFlag (which may be 0, 1 or 2).
-**
-** 1. Regardless of the value of createFlag, the cache is searched for a
-** copy of the requested page. If one is found, it is returned.
-**
-** 2. If createFlag==0 and the page is not already in the cache, NULL is
-** returned.
-**
-** 3. If createFlag is 1, and the page is not already in the cache, then
-** return NULL (do not allocate a new page) if any of the following
-** conditions are true:
-**
-** (a) the number of pages pinned by the cache is greater than
-** PCache1.nMax, or
-**
-** (b) the number of pages pinned by the cache is greater than
-** the sum of nMax for all purgeable caches, less the sum of
-** nMin for all other purgeable caches, or
-**
-** 4. If none of the first three conditions apply and the cache is marked
-** as purgeable, and if one of the following is true:
-**
-** (a) The number of pages allocated for the cache is already
-** PCache1.nMax, or
-**
-** (b) The number of pages allocated for all purgeable caches is
-** already equal to or greater than the sum of nMax for all
-** purgeable caches,
-**
-** (c) The system is under memory pressure and wants to avoid
-** unnecessary pages cache entry allocations
-**
-** then attempt to recycle a page from the LRU list. If it is the right
-** size, return the recycled buffer. Otherwise, free the buffer and
-** proceed to step 5.
-**
-** 5. Otherwise, allocate and return a new page buffer.
+** This steps are broken out into a separate procedure because they are
+** usually not needed, and by avoiding the stack initialization required
+** for these steps, the main pcache1Fetch() procedure can run faster.
*/
-static sqlite3_pcache_page *pcache1Fetch(
- sqlite3_pcache *p,
+static SQLITE_NOINLINE PgHdr1 *pcache1FetchStage2(
+ PCache1 *pCache,
unsigned int iKey,
int createFlag
){
unsigned int nPinned;
- PCache1 *pCache = (PCache1 *)p;
- PGroup *pGroup;
+ PGroup *pGroup = pCache->pGroup;
PgHdr1 *pPage = 0;
- assert( offsetof(PgHdr1,page)==0 );
- assert( pCache->bPurgeable || createFlag!=1 );
- assert( pCache->bPurgeable || pCache->nMin==0 );
- assert( pCache->bPurgeable==0 || pCache->nMin==10 );
- assert( pCache->nMin==0 || pCache->bPurgeable );
- pcache1EnterMutex(pGroup = pCache->pGroup);
-
- /* Step 1: Search the hash table for an existing entry. */
- if( pCache->nHash>0 ){
- unsigned int h = iKey % pCache->nHash;
- for(pPage=pCache->apHash[h]; pPage&&pPage->iKey!=iKey; pPage=pPage->pNext);
- }
-
- /* Step 2: Abort if no existing page is found and createFlag is 0 */
- if( pPage ){
- if( !pPage->isPinned ) pcache1PinPage(pPage);
- goto fetch_out;
- }
- if( createFlag==0 ){
- goto fetch_out;
- }
-
- /* The pGroup local variable will normally be initialized by the
- ** pcache1EnterMutex() macro above. But if SQLITE_MUTEX_OMIT is defined,
- ** then pcache1EnterMutex() is a no-op, so we have to initialize the
- ** local variable here. Delaying the initialization of pGroup is an
- ** optimization: The common case is to exit the module before reaching
- ** this point.
- */
-#ifdef SQLITE_MUTEX_OMIT
- pGroup = pCache->pGroup;
-#endif
-
/* Step 3: Abort if createFlag is 1 but the cache is nearly full */
assert( pCache->nPage >= pCache->nRecyclable );
nPinned = pCache->nPage - pCache->nRecyclable;
|| nPinned>=pCache->n90pct
|| pcache1UnderMemoryPressure(pCache)
)){
- goto fetch_out;
+ return 0;
}
- if( pCache->nPage>=pCache->nHash && pcache1ResizeHash(pCache) ){
- goto fetch_out;
- }
+ if( pCache->nPage>=pCache->nHash ) pcache1ResizeHash(pCache);
assert( pCache->nHash>0 && pCache->apHash );
/* Step 4. Try to recycle a page. */
pPage->isPinned = 1;
*(void **)pPage->page.pExtra = 0;
pCache->apHash[h] = pPage;
+ if( iKey>pCache->iMaxKey ){
+ pCache->iMaxKey = iKey;
+ }
}
+ return pPage;
+}
+
+/*
+** Implementation of the sqlite3_pcache.xFetch method.
+**
+** Fetch a page by key value.
+**
+** Whether or not a new page may be allocated by this function depends on
+** the value of the createFlag argument. 0 means do not allocate a new
+** page. 1 means allocate a new page if space is easily available. 2
+** means to try really hard to allocate a new page.
+**
+** For a non-purgeable cache (a cache used as the storage for an in-memory
+** database) there is really no difference between createFlag 1 and 2. So
+** the calling function (pcache.c) will never have a createFlag of 1 on
+** a non-purgeable cache.
+**
+** There are three different approaches to obtaining space for a page,
+** depending on the value of parameter createFlag (which may be 0, 1 or 2).
+**
+** 1. Regardless of the value of createFlag, the cache is searched for a
+** copy of the requested page. If one is found, it is returned.
+**
+** 2. If createFlag==0 and the page is not already in the cache, NULL is
+** returned.
+**
+** 3. If createFlag is 1, and the page is not already in the cache, then
+** return NULL (do not allocate a new page) if any of the following
+** conditions are true:
+**
+** (a) the number of pages pinned by the cache is greater than
+** PCache1.nMax, or
+**
+** (b) the number of pages pinned by the cache is greater than
+** the sum of nMax for all purgeable caches, less the sum of
+** nMin for all other purgeable caches, or
+**
+** 4. If none of the first three conditions apply and the cache is marked
+** as purgeable, and if one of the following is true:
+**
+** (a) The number of pages allocated for the cache is already
+** PCache1.nMax, or
+**
+** (b) The number of pages allocated for all purgeable caches is
+** already equal to or greater than the sum of nMax for all
+** purgeable caches,
+**
+** (c) The system is under memory pressure and wants to avoid
+** unnecessary pages cache entry allocations
+**
+** then attempt to recycle a page from the LRU list. If it is the right
+** size, return the recycled buffer. Otherwise, free the buffer and
+** proceed to step 5.
+**
+** 5. Otherwise, allocate and return a new page buffer.
+*/
+static sqlite3_pcache_page *pcache1Fetch(
+ sqlite3_pcache *p,
+ unsigned int iKey,
+ int createFlag
+){
+ PCache1 *pCache = (PCache1 *)p;
+ PgHdr1 *pPage = 0;
+
+ assert( offsetof(PgHdr1,page)==0 );
+ assert( pCache->bPurgeable || createFlag!=1 );
+ assert( pCache->bPurgeable || pCache->nMin==0 );
+ assert( pCache->bPurgeable==0 || pCache->nMin==10 );
+ assert( pCache->nMin==0 || pCache->bPurgeable );
+ assert( pCache->nHash>0 );
+ pcache1EnterMutex(pCache->pGroup);
+
+ /* Step 1: Search the hash table for an existing entry. */
+ pPage = pCache->apHash[iKey % pCache->nHash];
+ while( pPage && pPage->iKey!=iKey ){ pPage = pPage->pNext; }
-fetch_out:
- if( pPage && iKey>pCache->iMaxKey ){
- pCache->iMaxKey = iKey;
+ /* Step 2: Abort if no existing page is found and createFlag is 0 */
+ if( pPage ){
+ if( !pPage->isPinned ) pcache1PinPage(pPage);
+ }else if( createFlag ){
+ /* Steps 3, 4, and 5 implemented by this subroutine */
+ pPage = pcache1FetchStage2(pCache, iKey, createFlag);
}
- pcache1LeaveMutex(pGroup);
+ assert( pPage==0 || pCache->iMaxKey>=iKey );
+ pcache1LeaveMutex(pCache->pGroup);
return (sqlite3_pcache_page*)pPage;
}
projects / thirdparty / sqlite.git / commitdiff
