diff options
author | Hans-Christoph Steiner <hans@eds.org> | 2012-03-30 20:42:12 -0400 |
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committer | Hans-Christoph Steiner <hans@eds.org> | 2012-03-30 20:42:12 -0400 |
commit | 7bb481fda9ecb134804b49c2ce77ca28f7eea583 (patch) | |
tree | 31b520b9914d3e2453968abe375f2c102772c3dc /src/pcache1.c |
Imported Upstream version 2.0.3
Diffstat (limited to 'src/pcache1.c')
-rw-r--r-- | src/pcache1.c | 972 |
1 files changed, 972 insertions, 0 deletions
diff --git a/src/pcache1.c b/src/pcache1.c new file mode 100644 index 0000000..077a7b2 --- /dev/null +++ b/src/pcache1.c @@ -0,0 +1,972 @@ +/* +** 2008 November 05 +** +** The author disclaims copyright to this source code. In place of +** a legal notice, here is a blessing: +** +** May you do good and not evil. +** May you find forgiveness for yourself and forgive others. +** May you share freely, never taking more than you give. +** +************************************************************************* +** +** This file implements the default page cache implementation (the +** sqlite3_pcache interface). It also contains part of the implementation +** of the SQLITE_CONFIG_PAGECACHE and sqlite3_release_memory() features. +** If the default page cache implementation is overriden, then neither of +** these two features are available. +*/ + +#include "sqliteInt.h" + +typedef struct PCache1 PCache1; +typedef struct PgHdr1 PgHdr1; +typedef struct PgFreeslot PgFreeslot; +typedef struct PGroup PGroup; + + +/* Each page cache (or PCache) belongs to a PGroup. A PGroup is a set +** of one or more PCaches that are able to recycle each others unpinned +** pages when they are under memory pressure. A PGroup is an instance of +** the following object. +** +** This page cache implementation works in one of two modes: +** +** (1) Every PCache is the sole member of its own PGroup. There is +** one PGroup per PCache. +** +** (2) There is a single global PGroup that all PCaches are a member +** of. +** +** Mode 1 uses more memory (since PCache instances are not able to rob +** unused pages from other PCaches) but it also operates without a mutex, +** and is therefore often faster. Mode 2 requires a mutex in order to be +** threadsafe, but is able recycle pages more efficient. +** +** For mode (1), PGroup.mutex is NULL. For mode (2) there is only a single +** PGroup which is the pcache1.grp global variable and its mutex is +** SQLITE_MUTEX_STATIC_LRU. +*/ +struct PGroup { + sqlite3_mutex *mutex; /* MUTEX_STATIC_LRU or NULL */ + int nMaxPage; /* Sum of nMax for purgeable caches */ + int nMinPage; /* Sum of nMin for purgeable caches */ + int mxPinned; /* nMaxpage + 10 - nMinPage */ + int nCurrentPage; /* Number of purgeable pages allocated */ + PgHdr1 *pLruHead, *pLruTail; /* LRU list of unpinned pages */ +}; + +/* Each page cache is an instance of the following object. Every +** open database file (including each in-memory database and each +** temporary or transient database) has a single page cache which +** is an instance of this object. +** +** Pointers to structures of this type are cast and returned as +** opaque sqlite3_pcache* handles. +*/ +struct PCache1 { + /* Cache configuration parameters. Page size (szPage) and the purgeable + ** flag (bPurgeable) are set when the cache is created. nMax may be + ** modified at any time by a call to the pcache1CacheSize() method. + ** The PGroup mutex must be held when accessing nMax. + */ + PGroup *pGroup; /* PGroup this cache belongs to */ + int szPage; /* Size of allocated pages in bytes */ + int bPurgeable; /* True if cache is purgeable */ + unsigned int nMin; /* Minimum number of pages reserved */ + unsigned int nMax; /* Configured "cache_size" value */ + unsigned int n90pct; /* nMax*9/10 */ + + /* Hash table of all pages. The following variables may only be accessed + ** when the accessor is holding the PGroup mutex. + */ + unsigned int nRecyclable; /* Number of pages in the LRU list */ + unsigned int nPage; /* Total number of pages in apHash */ + unsigned int nHash; /* Number of slots in apHash[] */ + PgHdr1 **apHash; /* Hash table for fast lookup by key */ + + unsigned int iMaxKey; /* Largest key seen since xTruncate() */ +}; + +/* +** Each cache entry is represented by an instance of the following +** structure. A buffer of PgHdr1.pCache->szPage bytes is allocated +** directly before this structure in memory (see the PGHDR1_TO_PAGE() +** macro below). +*/ +struct PgHdr1 { + unsigned int iKey; /* Key value (page number) */ + PgHdr1 *pNext; /* Next in hash table chain */ + PCache1 *pCache; /* Cache that currently owns this page */ + PgHdr1 *pLruNext; /* Next in LRU list of unpinned pages */ + PgHdr1 *pLruPrev; /* Previous in LRU list of unpinned pages */ +}; + +/* +** Free slots in the allocator used to divide up the buffer provided using +** the SQLITE_CONFIG_PAGECACHE mechanism. +*/ +struct PgFreeslot { + PgFreeslot *pNext; /* Next free slot */ +}; + +/* +** Global data used by this cache. +*/ +static SQLITE_WSD struct PCacheGlobal { + PGroup grp; /* The global PGroup for mode (2) */ + + /* Variables related to SQLITE_CONFIG_PAGECACHE settings. The + ** szSlot, nSlot, pStart, pEnd, nReserve, and isInit values are all + ** fixed at sqlite3_initialize() time and do not require mutex protection. + ** The nFreeSlot and pFree values do require mutex protection. + */ + int isInit; /* True if initialized */ + int szSlot; /* Size of each free slot */ + int nSlot; /* The number of pcache slots */ + int nReserve; /* Try to keep nFreeSlot above this */ + void *pStart, *pEnd; /* Bounds of pagecache malloc range */ + /* Above requires no mutex. Use mutex below for variable that follow. */ + sqlite3_mutex *mutex; /* Mutex for accessing the following: */ + int nFreeSlot; /* Number of unused pcache slots */ + PgFreeslot *pFree; /* Free page blocks */ + /* The following value requires a mutex to change. We skip the mutex on + ** reading because (1) most platforms read a 32-bit integer atomically and + ** (2) even if an incorrect value is read, no great harm is done since this + ** is really just an optimization. */ + int bUnderPressure; /* True if low on PAGECACHE memory */ +} pcache1_g; + +/* +** All code in this file should access the global structure above via the +** alias "pcache1". This ensures that the WSD emulation is used when +** compiling for systems that do not support real WSD. +*/ +#define pcache1 (GLOBAL(struct PCacheGlobal, pcache1_g)) + +/* +** When a PgHdr1 structure is allocated, the associated PCache1.szPage +** bytes of data are located directly before it in memory (i.e. the total +** size of the allocation is sizeof(PgHdr1)+PCache1.szPage byte). The +** PGHDR1_TO_PAGE() macro takes a pointer to a PgHdr1 structure as +** an argument and returns a pointer to the associated block of szPage +** bytes. The PAGE_TO_PGHDR1() macro does the opposite: its argument is +** a pointer to a block of szPage bytes of data and the return value is +** a pointer to the associated PgHdr1 structure. +** +** assert( PGHDR1_TO_PAGE(PAGE_TO_PGHDR1(pCache, X))==X ); +*/ +#define PGHDR1_TO_PAGE(p) (void*)(((char*)p) - p->pCache->szPage) +#define PAGE_TO_PGHDR1(c, p) (PgHdr1*)(((char*)p) + c->szPage) + +/* +** Macros to enter and leave the PCache LRU mutex. +*/ +#define pcache1EnterMutex(X) sqlite3_mutex_enter((X)->mutex) +#define pcache1LeaveMutex(X) sqlite3_mutex_leave((X)->mutex) + +/******************************************************************************/ +/******** Page Allocation/SQLITE_CONFIG_PCACHE Related Functions **************/ + +/* +** This function is called during initialization if a static buffer is +** supplied to use for the page-cache by passing the SQLITE_CONFIG_PAGECACHE +** verb to sqlite3_config(). Parameter pBuf points to an allocation large +** enough to contain 'n' buffers of 'sz' bytes each. +** +** This routine is called from sqlite3_initialize() and so it is guaranteed +** to be serialized already. There is no need for further mutexing. +*/ +void sqlite3PCacheBufferSetup(void *pBuf, int sz, int n){ + if( pcache1.isInit ){ + PgFreeslot *p; + sz = ROUNDDOWN8(sz); + pcache1.szSlot = sz; + pcache1.nSlot = pcache1.nFreeSlot = n; + pcache1.nReserve = n>90 ? 10 : (n/10 + 1); + pcache1.pStart = pBuf; + pcache1.pFree = 0; + pcache1.bUnderPressure = 0; + while( n-- ){ + p = (PgFreeslot*)pBuf; + p->pNext = pcache1.pFree; + pcache1.pFree = p; + pBuf = (void*)&((char*)pBuf)[sz]; + } + pcache1.pEnd = pBuf; + } +} + +/* +** Malloc function used within this file to allocate space from the buffer +** configured using sqlite3_config(SQLITE_CONFIG_PAGECACHE) option. If no +** such buffer exists or there is no space left in it, this function falls +** back to sqlite3Malloc(). +** +** Multiple threads can run this routine at the same time. Global variables +** in pcache1 need to be protected via mutex. +*/ +static void *pcache1Alloc(int nByte){ + void *p = 0; + assert( sqlite3_mutex_notheld(pcache1.grp.mutex) ); + sqlite3StatusSet(SQLITE_STATUS_PAGECACHE_SIZE, nByte); + if( nByte<=pcache1.szSlot ){ + sqlite3_mutex_enter(pcache1.mutex); + p = (PgHdr1 *)pcache1.pFree; + if( p ){ + pcache1.pFree = pcache1.pFree->pNext; + pcache1.nFreeSlot--; + pcache1.bUnderPressure = pcache1.nFreeSlot<pcache1.nReserve; + assert( pcache1.nFreeSlot>=0 ); + sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_USED, 1); + } + sqlite3_mutex_leave(pcache1.mutex); + } + if( p==0 ){ + /* Memory is not available in the SQLITE_CONFIG_PAGECACHE pool. Get + ** it from sqlite3Malloc instead. + */ + p = sqlite3Malloc(nByte); + if( p ){ + int sz = sqlite3MallocSize(p); + sqlite3_mutex_enter(pcache1.mutex); + sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_OVERFLOW, sz); + sqlite3_mutex_leave(pcache1.mutex); + } + sqlite3MemdebugSetType(p, MEMTYPE_PCACHE); + } + return p; +} + +/* +** Free an allocated buffer obtained from pcache1Alloc(). +*/ +static void pcache1Free(void *p){ + if( p==0 ) return; + if( p>=pcache1.pStart && p<pcache1.pEnd ){ + PgFreeslot *pSlot; + sqlite3_mutex_enter(pcache1.mutex); + sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_USED, -1); + pSlot = (PgFreeslot*)p; + pSlot->pNext = pcache1.pFree; + pcache1.pFree = pSlot; + pcache1.nFreeSlot++; + pcache1.bUnderPressure = pcache1.nFreeSlot<pcache1.nReserve; + assert( pcache1.nFreeSlot<=pcache1.nSlot ); + sqlite3_mutex_leave(pcache1.mutex); + }else{ + int iSize; + assert( sqlite3MemdebugHasType(p, MEMTYPE_PCACHE) ); + sqlite3MemdebugSetType(p, MEMTYPE_HEAP); + iSize = sqlite3MallocSize(p); + sqlite3_mutex_enter(pcache1.mutex); + sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_OVERFLOW, -iSize); + sqlite3_mutex_leave(pcache1.mutex); + sqlite3_free(p); + } +} + +#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT +/* +** Return the size of a pcache allocation +*/ +static int pcache1MemSize(void *p){ + if( p>=pcache1.pStart && p<pcache1.pEnd ){ + return pcache1.szSlot; + }else{ + int iSize; + assert( sqlite3MemdebugHasType(p, MEMTYPE_PCACHE) ); + sqlite3MemdebugSetType(p, MEMTYPE_HEAP); + iSize = sqlite3MallocSize(p); + sqlite3MemdebugSetType(p, MEMTYPE_PCACHE); + return iSize; + } +} +#endif /* SQLITE_ENABLE_MEMORY_MANAGEMENT */ + +/* +** Allocate a new page object initially associated with cache pCache. +*/ +static PgHdr1 *pcache1AllocPage(PCache1 *pCache){ + int nByte = sizeof(PgHdr1) + pCache->szPage; + PgHdr1 *p = 0; + void *pPg; + + /* The group mutex must be released before pcache1Alloc() is called. This + ** is because it may call sqlite3_release_memory(), which assumes that + ** this mutex is not held. */ + assert( sqlite3_mutex_held(pCache->pGroup->mutex) ); + pcache1LeaveMutex(pCache->pGroup); + pPg = pcache1Alloc(nByte); + pcache1EnterMutex(pCache->pGroup); + + if( pPg ){ + p = PAGE_TO_PGHDR1(pCache, pPg); + if( pCache->bPurgeable ){ + pCache->pGroup->nCurrentPage++; + } + } + return p; +} + +/* +** Free a page object allocated by pcache1AllocPage(). +** +** The pointer is allowed to be NULL, which is prudent. But it turns out +** that the current implementation happens to never call this routine +** with a NULL pointer, so we mark the NULL test with ALWAYS(). +*/ +static void pcache1FreePage(PgHdr1 *p){ + if( ALWAYS(p) ){ + PCache1 *pCache = p->pCache; + assert( sqlite3_mutex_held(p->pCache->pGroup->mutex) ); + pcache1Free(PGHDR1_TO_PAGE(p)); + if( pCache->bPurgeable ){ + pCache->pGroup->nCurrentPage--; + } + } +} + +/* +** Malloc function used by SQLite to obtain space from the buffer configured +** using sqlite3_config(SQLITE_CONFIG_PAGECACHE) option. If no such buffer +** exists, this function falls back to sqlite3Malloc(). +*/ +void *sqlite3PageMalloc(int sz){ + return pcache1Alloc(sz); +} + +/* +** Free an allocated buffer obtained from sqlite3PageMalloc(). +*/ +void sqlite3PageFree(void *p){ + pcache1Free(p); +} + + +/* +** Return true if it desirable to avoid allocating a new page cache +** entry. +** +** If memory was allocated specifically to the page cache using +** SQLITE_CONFIG_PAGECACHE but that memory has all been used, then +** it is desirable to avoid allocating a new page cache entry because +** presumably SQLITE_CONFIG_PAGECACHE was suppose to be sufficient +** for all page cache needs and we should not need to spill the +** allocation onto the heap. +** +** Or, the heap is used for all page cache memory put the heap is +** under memory pressure, then again it is desirable to avoid +** allocating a new page cache entry in order to avoid stressing +** the heap even further. +*/ +static int pcache1UnderMemoryPressure(PCache1 *pCache){ + if( pcache1.nSlot && pCache->szPage<=pcache1.szSlot ){ + return pcache1.bUnderPressure; + }else{ + return sqlite3HeapNearlyFull(); + } +} + +/******************************************************************************/ +/******** General Implementation Functions ************************************/ + +/* +** This function is used to resize the hash table used by the cache passed +** as the first argument. +** +** The PCache mutex must be held when this function is called. +*/ +static int pcache1ResizeHash(PCache1 *p){ + PgHdr1 **apNew; + unsigned int nNew; + unsigned int i; + + assert( sqlite3_mutex_held(p->pGroup->mutex) ); + + nNew = p->nHash*2; + if( nNew<256 ){ + nNew = 256; + } + + pcache1LeaveMutex(p->pGroup); + if( p->nHash ){ sqlite3BeginBenignMalloc(); } + apNew = (PgHdr1 **)sqlite3_malloc(sizeof(PgHdr1 *)*nNew); + if( p->nHash ){ sqlite3EndBenignMalloc(); } + pcache1EnterMutex(p->pGroup); + if( apNew ){ + memset(apNew, 0, sizeof(PgHdr1 *)*nNew); + for(i=0; i<p->nHash; i++){ + PgHdr1 *pPage; + PgHdr1 *pNext = p->apHash[i]; + while( (pPage = pNext)!=0 ){ + unsigned int h = pPage->iKey % nNew; + pNext = pPage->pNext; + pPage->pNext = apNew[h]; + apNew[h] = pPage; + } + } + sqlite3_free(p->apHash); + p->apHash = apNew; + p->nHash = nNew; + } + + return (p->apHash ? SQLITE_OK : SQLITE_NOMEM); +} + +/* +** This function is used internally to remove the page pPage from the +** PGroup LRU list, if is part of it. If pPage is not part of the PGroup +** LRU list, then this function is a no-op. +** +** The PGroup mutex must be held when this function is called. +** +** If pPage is NULL then this routine is a no-op. +*/ +static void pcache1PinPage(PgHdr1 *pPage){ + PCache1 *pCache; + PGroup *pGroup; + + if( pPage==0 ) return; + pCache = pPage->pCache; + pGroup = pCache->pGroup; + assert( sqlite3_mutex_held(pGroup->mutex) ); + if( pPage->pLruNext || pPage==pGroup->pLruTail ){ + if( pPage->pLruPrev ){ + pPage->pLruPrev->pLruNext = pPage->pLruNext; + } + if( pPage->pLruNext ){ + pPage->pLruNext->pLruPrev = pPage->pLruPrev; + } + if( pGroup->pLruHead==pPage ){ + pGroup->pLruHead = pPage->pLruNext; + } + if( pGroup->pLruTail==pPage ){ + pGroup->pLruTail = pPage->pLruPrev; + } + pPage->pLruNext = 0; + pPage->pLruPrev = 0; + pPage->pCache->nRecyclable--; + } +} + + +/* +** Remove the page supplied as an argument from the hash table +** (PCache1.apHash structure) that it is currently stored in. +** +** The PGroup mutex must be held when this function is called. +*/ +static void pcache1RemoveFromHash(PgHdr1 *pPage){ + unsigned int h; + PCache1 *pCache = pPage->pCache; + PgHdr1 **pp; + + assert( sqlite3_mutex_held(pCache->pGroup->mutex) ); + h = pPage->iKey % pCache->nHash; + for(pp=&pCache->apHash[h]; (*pp)!=pPage; pp=&(*pp)->pNext); + *pp = (*pp)->pNext; + + pCache->nPage--; +} + +/* +** If there are currently more than nMaxPage pages allocated, try +** to recycle pages to reduce the number allocated to nMaxPage. +*/ +static void pcache1EnforceMaxPage(PGroup *pGroup){ + assert( sqlite3_mutex_held(pGroup->mutex) ); + while( pGroup->nCurrentPage>pGroup->nMaxPage && pGroup->pLruTail ){ + PgHdr1 *p = pGroup->pLruTail; + assert( p->pCache->pGroup==pGroup ); + pcache1PinPage(p); + pcache1RemoveFromHash(p); + pcache1FreePage(p); + } +} + +/* +** Discard all pages from cache pCache with a page number (key value) +** greater than or equal to iLimit. Any pinned pages that meet this +** criteria are unpinned before they are discarded. +** +** The PCache mutex must be held when this function is called. +*/ +static void pcache1TruncateUnsafe( + PCache1 *pCache, /* The cache to truncate */ + unsigned int iLimit /* Drop pages with this pgno or larger */ +){ + TESTONLY( unsigned int nPage = 0; ) /* To assert pCache->nPage is correct */ + unsigned int h; + assert( sqlite3_mutex_held(pCache->pGroup->mutex) ); + for(h=0; h<pCache->nHash; h++){ + PgHdr1 **pp = &pCache->apHash[h]; + PgHdr1 *pPage; + while( (pPage = *pp)!=0 ){ + if( pPage->iKey>=iLimit ){ + pCache->nPage--; + *pp = pPage->pNext; + pcache1PinPage(pPage); + pcache1FreePage(pPage); + }else{ + pp = &pPage->pNext; + TESTONLY( nPage++; ) + } + } + } + assert( pCache->nPage==nPage ); +} + +/******************************************************************************/ +/******** sqlite3_pcache Methods **********************************************/ + +/* +** Implementation of the sqlite3_pcache.xInit method. +*/ +static int pcache1Init(void *NotUsed){ + UNUSED_PARAMETER(NotUsed); + assert( pcache1.isInit==0 ); + memset(&pcache1, 0, sizeof(pcache1)); + if( sqlite3GlobalConfig.bCoreMutex ){ + pcache1.grp.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_LRU); + pcache1.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_PMEM); + } + pcache1.grp.mxPinned = 10; + pcache1.isInit = 1; + return SQLITE_OK; +} + +/* +** Implementation of the sqlite3_pcache.xShutdown method. +** Note that the static mutex allocated in xInit does +** not need to be freed. +*/ +static void pcache1Shutdown(void *NotUsed){ + UNUSED_PARAMETER(NotUsed); + assert( pcache1.isInit!=0 ); + memset(&pcache1, 0, sizeof(pcache1)); +} + +/* +** Implementation of the sqlite3_pcache.xCreate method. +** +** Allocate a new cache. +*/ +static sqlite3_pcache *pcache1Create(int szPage, int bPurgeable){ + PCache1 *pCache; /* The newly created page cache */ + PGroup *pGroup; /* The group the new page cache will belong to */ + int sz; /* Bytes of memory required to allocate the new cache */ + + /* + ** The seperateCache variable is true if each PCache has its own private + ** PGroup. In other words, separateCache is true for mode (1) where no + ** mutexing is required. + ** + ** * Always use a unified cache (mode-2) if ENABLE_MEMORY_MANAGEMENT + ** + ** * Always use a unified cache in single-threaded applications + ** + ** * Otherwise (if multi-threaded and ENABLE_MEMORY_MANAGEMENT is off) + ** use separate caches (mode-1) + */ +#if defined(SQLITE_ENABLE_MEMORY_MANAGEMENT) || SQLITE_THREADSAFE==0 + const int separateCache = 0; +#else + int separateCache = sqlite3GlobalConfig.bCoreMutex>0; +#endif + + sz = sizeof(PCache1) + sizeof(PGroup)*separateCache; + pCache = (PCache1 *)sqlite3_malloc(sz); + if( pCache ){ + memset(pCache, 0, sz); + if( separateCache ){ + pGroup = (PGroup*)&pCache[1]; + pGroup->mxPinned = 10; + }else{ + pGroup = &pcache1.grp; + } + pCache->pGroup = pGroup; + pCache->szPage = szPage; + pCache->bPurgeable = (bPurgeable ? 1 : 0); + if( bPurgeable ){ + pCache->nMin = 10; + pcache1EnterMutex(pGroup); + pGroup->nMinPage += pCache->nMin; + pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage; + pcache1LeaveMutex(pGroup); + } + } + return (sqlite3_pcache *)pCache; +} + +/* +** Implementation of the sqlite3_pcache.xCachesize method. +** +** Configure the cache_size limit for a cache. +*/ +static void pcache1Cachesize(sqlite3_pcache *p, int nMax){ + PCache1 *pCache = (PCache1 *)p; + if( pCache->bPurgeable ){ + PGroup *pGroup = pCache->pGroup; + pcache1EnterMutex(pGroup); + pGroup->nMaxPage += (nMax - pCache->nMax); + pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage; + pCache->nMax = nMax; + pCache->n90pct = pCache->nMax*9/10; + pcache1EnforceMaxPage(pGroup); + pcache1LeaveMutex(pGroup); + } +} + +/* +** Implementation of the sqlite3_pcache.xPagecount method. +*/ +static int pcache1Pagecount(sqlite3_pcache *p){ + int n; + PCache1 *pCache = (PCache1*)p; + pcache1EnterMutex(pCache->pGroup); + n = pCache->nPage; + pcache1LeaveMutex(pCache->pGroup); + return n; +} + +/* +** 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-purgable 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 void *pcache1Fetch(sqlite3_pcache *p, unsigned int iKey, int createFlag){ + int nPinned; + PCache1 *pCache = (PCache1 *)p; + PGroup *pGroup; + PgHdr1 *pPage = 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 || createFlag==0 ){ + pcache1PinPage(pPage); + 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 */ + nPinned = pCache->nPage - pCache->nRecyclable; + assert( nPinned>=0 ); + assert( pGroup->mxPinned == pGroup->nMaxPage + 10 - pGroup->nMinPage ); + assert( pCache->n90pct == pCache->nMax*9/10 ); + if( createFlag==1 && ( + nPinned>=pGroup->mxPinned + || nPinned>=(int)pCache->n90pct + || pcache1UnderMemoryPressure(pCache) + )){ + goto fetch_out; + } + + if( pCache->nPage>=pCache->nHash && pcache1ResizeHash(pCache) ){ + goto fetch_out; + } + + /* Step 4. Try to recycle a page. */ + if( pCache->bPurgeable && pGroup->pLruTail && ( + (pCache->nPage+1>=pCache->nMax) + || pGroup->nCurrentPage>=pGroup->nMaxPage + || pcache1UnderMemoryPressure(pCache) + )){ + PCache1 *pOtherCache; + pPage = pGroup->pLruTail; + pcache1RemoveFromHash(pPage); + pcache1PinPage(pPage); + if( (pOtherCache = pPage->pCache)->szPage!=pCache->szPage ){ + pcache1FreePage(pPage); + pPage = 0; + }else{ + pGroup->nCurrentPage -= + (pOtherCache->bPurgeable - pCache->bPurgeable); + } + } + + /* Step 5. If a usable page buffer has still not been found, + ** attempt to allocate a new one. + */ + if( !pPage ){ + if( createFlag==1 ) sqlite3BeginBenignMalloc(); + pPage = pcache1AllocPage(pCache); + if( createFlag==1 ) sqlite3EndBenignMalloc(); + } + + if( pPage ){ + unsigned int h = iKey % pCache->nHash; + pCache->nPage++; + pPage->iKey = iKey; + pPage->pNext = pCache->apHash[h]; + pPage->pCache = pCache; + pPage->pLruPrev = 0; + pPage->pLruNext = 0; + *(void **)(PGHDR1_TO_PAGE(pPage)) = 0; + pCache->apHash[h] = pPage; + } + +fetch_out: + if( pPage && iKey>pCache->iMaxKey ){ + pCache->iMaxKey = iKey; + } + pcache1LeaveMutex(pGroup); + return (pPage ? PGHDR1_TO_PAGE(pPage) : 0); +} + + +/* +** Implementation of the sqlite3_pcache.xUnpin method. +** +** Mark a page as unpinned (eligible for asynchronous recycling). +*/ +static void pcache1Unpin(sqlite3_pcache *p, void *pPg, int reuseUnlikely){ + PCache1 *pCache = (PCache1 *)p; + PgHdr1 *pPage = PAGE_TO_PGHDR1(pCache, pPg); + PGroup *pGroup = pCache->pGroup; + + assert( pPage->pCache==pCache ); + pcache1EnterMutex(pGroup); + + /* It is an error to call this function if the page is already + ** part of the PGroup LRU list. + */ + assert( pPage->pLruPrev==0 && pPage->pLruNext==0 ); + assert( pGroup->pLruHead!=pPage && pGroup->pLruTail!=pPage ); + + if( reuseUnlikely || pGroup->nCurrentPage>pGroup->nMaxPage ){ + pcache1RemoveFromHash(pPage); + pcache1FreePage(pPage); + }else{ + /* Add the page to the PGroup LRU list. */ + if( pGroup->pLruHead ){ + pGroup->pLruHead->pLruPrev = pPage; + pPage->pLruNext = pGroup->pLruHead; + pGroup->pLruHead = pPage; + }else{ + pGroup->pLruTail = pPage; + pGroup->pLruHead = pPage; + } + pCache->nRecyclable++; + } + + pcache1LeaveMutex(pCache->pGroup); +} + +/* +** Implementation of the sqlite3_pcache.xRekey method. +*/ +static void pcache1Rekey( + sqlite3_pcache *p, + void *pPg, + unsigned int iOld, + unsigned int iNew +){ + PCache1 *pCache = (PCache1 *)p; + PgHdr1 *pPage = PAGE_TO_PGHDR1(pCache, pPg); + PgHdr1 **pp; + unsigned int h; + assert( pPage->iKey==iOld ); + assert( pPage->pCache==pCache ); + + pcache1EnterMutex(pCache->pGroup); + + h = iOld%pCache->nHash; + pp = &pCache->apHash[h]; + while( (*pp)!=pPage ){ + pp = &(*pp)->pNext; + } + *pp = pPage->pNext; + + h = iNew%pCache->nHash; + pPage->iKey = iNew; + pPage->pNext = pCache->apHash[h]; + pCache->apHash[h] = pPage; + if( iNew>pCache->iMaxKey ){ + pCache->iMaxKey = iNew; + } + + pcache1LeaveMutex(pCache->pGroup); +} + +/* +** Implementation of the sqlite3_pcache.xTruncate method. +** +** Discard all unpinned pages in the cache with a page number equal to +** or greater than parameter iLimit. Any pinned pages with a page number +** equal to or greater than iLimit are implicitly unpinned. +*/ +static void pcache1Truncate(sqlite3_pcache *p, unsigned int iLimit){ + PCache1 *pCache = (PCache1 *)p; + pcache1EnterMutex(pCache->pGroup); + if( iLimit<=pCache->iMaxKey ){ + pcache1TruncateUnsafe(pCache, iLimit); + pCache->iMaxKey = iLimit-1; + } + pcache1LeaveMutex(pCache->pGroup); +} + +/* +** Implementation of the sqlite3_pcache.xDestroy method. +** +** Destroy a cache allocated using pcache1Create(). +*/ +static void pcache1Destroy(sqlite3_pcache *p){ + PCache1 *pCache = (PCache1 *)p; + PGroup *pGroup = pCache->pGroup; + assert( pCache->bPurgeable || (pCache->nMax==0 && pCache->nMin==0) ); + pcache1EnterMutex(pGroup); + pcache1TruncateUnsafe(pCache, 0); + pGroup->nMaxPage -= pCache->nMax; + pGroup->nMinPage -= pCache->nMin; + pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage; + pcache1EnforceMaxPage(pGroup); + pcache1LeaveMutex(pGroup); + sqlite3_free(pCache->apHash); + sqlite3_free(pCache); +} + +/* +** This function is called during initialization (sqlite3_initialize()) to +** install the default pluggable cache module, assuming the user has not +** already provided an alternative. +*/ +void sqlite3PCacheSetDefault(void){ + static const sqlite3_pcache_methods defaultMethods = { + 0, /* pArg */ + pcache1Init, /* xInit */ + pcache1Shutdown, /* xShutdown */ + pcache1Create, /* xCreate */ + pcache1Cachesize, /* xCachesize */ + pcache1Pagecount, /* xPagecount */ + pcache1Fetch, /* xFetch */ + pcache1Unpin, /* xUnpin */ + pcache1Rekey, /* xRekey */ + pcache1Truncate, /* xTruncate */ + pcache1Destroy /* xDestroy */ + }; + sqlite3_config(SQLITE_CONFIG_PCACHE, &defaultMethods); +} + +#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT +/* +** This function is called to free superfluous dynamically allocated memory +** held by the pager system. Memory in use by any SQLite pager allocated +** by the current thread may be sqlite3_free()ed. +** +** nReq is the number of bytes of memory required. Once this much has +** been released, the function returns. The return value is the total number +** of bytes of memory released. +*/ +int sqlite3PcacheReleaseMemory(int nReq){ + int nFree = 0; + assert( sqlite3_mutex_notheld(pcache1.grp.mutex) ); + assert( sqlite3_mutex_notheld(pcache1.mutex) ); + if( pcache1.pStart==0 ){ + PgHdr1 *p; + pcache1EnterMutex(&pcache1.grp); + while( (nReq<0 || nFree<nReq) && ((p=pcache1.grp.pLruTail)!=0) ){ + nFree += pcache1MemSize(PGHDR1_TO_PAGE(p)); + pcache1PinPage(p); + pcache1RemoveFromHash(p); + pcache1FreePage(p); + } + pcache1LeaveMutex(&pcache1.grp); + } + return nFree; +} +#endif /* SQLITE_ENABLE_MEMORY_MANAGEMENT */ + +#ifdef SQLITE_TEST +/* +** This function is used by test procedures to inspect the internal state +** of the global cache. +*/ +void sqlite3PcacheStats( + int *pnCurrent, /* OUT: Total number of pages cached */ + int *pnMax, /* OUT: Global maximum cache size */ + int *pnMin, /* OUT: Sum of PCache1.nMin for purgeable caches */ + int *pnRecyclable /* OUT: Total number of pages available for recycling */ +){ + PgHdr1 *p; + int nRecyclable = 0; + for(p=pcache1.grp.pLruHead; p; p=p->pLruNext){ + nRecyclable++; + } + *pnCurrent = pcache1.grp.nCurrentPage; + *pnMax = pcache1.grp.nMaxPage; + *pnMin = pcache1.grp.nMinPage; + *pnRecyclable = nRecyclable; +} +#endif |