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1021 lines (944 loc) · 32.3 KB
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/*
** 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 recycles pages more efficiently.
**
** 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 */
unsigned int nMaxPage; /* Sum of nMax for purgeable caches */
unsigned int nMinPage; /* Sum of nMin for purgeable caches */
unsigned int mxPinned; /* nMaxpage + 10 - nMinPage */
unsigned 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 szExtra; /* Size of extra space 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 */
unsigned int iMaxKey; /* Largest key seen since xTruncate() */
/* 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 */
};
/*
** Each cache entry is represented by an instance of the following
** structure. Unless SQLITE_PCACHE_SEPARATE_HEADER is defined, a buffer of
** PgHdr1.pCache->szPage bytes is allocated directly before this structure
** in memory.
*/
struct PgHdr1 {
sqlite3_pcache_page page;
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: */
PgFreeslot *pFree; /* Free page blocks */
int nFreeSlot; /* Number of unused pcache slots */
/* 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))
/*
** 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);
#ifndef SQLITE_DISABLE_PAGECACHE_OVERFLOW_STATS
if( p ){
int sz = sqlite3MallocSize(p);
sqlite3_mutex_enter(pcache1.mutex);
sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_OVERFLOW, sz);
sqlite3_mutex_leave(pcache1.mutex);
}
#endif
sqlite3MemdebugSetType(p, MEMTYPE_PCACHE);
}
return p;
}
/*
** Free an allocated buffer obtained from pcache1Alloc().
*/
static int pcache1Free(void *p){
int nFreed = 0;
if( p==0 ) return 0;
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{
assert( sqlite3MemdebugHasType(p, MEMTYPE_PCACHE) );
sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
nFreed = sqlite3MallocSize(p);
#ifndef SQLITE_DISABLE_PAGECACHE_OVERFLOW_STATS
sqlite3_mutex_enter(pcache1.mutex);
sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_OVERFLOW, -nFreed);
sqlite3_mutex_leave(pcache1.mutex);
#endif
sqlite3_free(p);
}
return nFreed;
}
#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){
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);
#ifdef SQLITE_PCACHE_SEPARATE_HEADER
pPg = pcache1Alloc(pCache->szPage);
p = sqlite3Malloc(sizeof(PgHdr1) + pCache->szExtra);
if( !pPg || !p ){
pcache1Free(pPg);
sqlite3_free(p);
pPg = 0;
}
#else
pPg = pcache1Alloc(sizeof(PgHdr1) + pCache->szPage + pCache->szExtra);
p = (PgHdr1 *)&((u8 *)pPg)[pCache->szPage];
#endif
pcache1EnterMutex(pCache->pGroup);
if( pPg ){
p->page.pBuf = pPg;
p->page.pExtra = &p[1];
if( pCache->bPurgeable ){
pCache->pGroup->nCurrentPage++;
}
return p;
}
return 0;
}
/*
** 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(p->page.pBuf);
#ifdef SQLITE_PCACHE_SEPARATE_HEADER
sqlite3_free(p);
#endif
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 but 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+pCache->szExtra)<=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 **)sqlite3MallocZero(sizeof(PgHdr1 *)*nNew);
if( p->nHash ){ sqlite3EndBenignMalloc(); }
pcache1EnterMutex(p->pGroup);
if( apNew ){
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 szExtra, 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 separateCache 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
assert( (szPage & (szPage-1))==0 && szPage>=512 && szPage<=65536 );
assert( szExtra < 300 );
sz = sizeof(PCache1) + sizeof(PGroup)*separateCache;
pCache = (PCache1 *)sqlite3MallocZero(sz);
if( pCache ){
if( separateCache ){
pGroup = (PGroup*)&pCache[1];
pGroup->mxPinned = 10;
}else{
pGroup = &pcache1.grp;
}
pCache->pGroup = pGroup;
pCache->szPage = szPage;
pCache->szExtra = szExtra;
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.xShrink method.
**
** Free up as much memory as possible.
*/
static void pcache1Shrink(sqlite3_pcache *p){
PCache1 *pCache = (PCache1*)p;
if( pCache->bPurgeable ){
PGroup *pGroup = pCache->pGroup;
int savedMaxPage;
pcache1EnterMutex(pGroup);
savedMaxPage = pGroup->nMaxPage;
pGroup->nMaxPage = 0;
pcache1EnforceMaxPage(pGroup);
pGroup->nMaxPage = savedMaxPage;
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-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
){
unsigned 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 */
assert( pCache->nPage >= pCache->nRecyclable );
nPinned = pCache->nPage - pCache->nRecyclable;
assert( pGroup->mxPinned == pGroup->nMaxPage + 10 - pGroup->nMinPage );
assert( pCache->n90pct == pCache->nMax*9/10 );
if( createFlag==1 && (
nPinned>=pGroup->mxPinned
|| nPinned>=pCache->n90pct
|| pcache1UnderMemoryPressure(pCache)
)){
goto fetch_out;
}
if( pCache->nPage>=pCache->nHash && pcache1ResizeHash(pCache) ){
goto fetch_out;
}
assert( pCache->nHash>0 && pCache->apHash );
/* Step 4. Try to recycle a page. */
if( pCache->bPurgeable && pGroup->pLruTail && (
(pCache->nPage+1>=pCache->nMax)
|| pGroup->nCurrentPage>=pGroup->nMaxPage
|| pcache1UnderMemoryPressure(pCache)
)){
PCache1 *pOther;
pPage = pGroup->pLruTail;
pcache1RemoveFromHash(pPage);
pcache1PinPage(pPage);
pOther = pPage->pCache;
/* We want to verify that szPage and szExtra are the same for pOther
** and pCache. Assert that we can verify this by comparing sums. */
assert( (pCache->szPage & (pCache->szPage-1))==0 && pCache->szPage>=512 );
assert( pCache->szExtra<512 );
assert( (pOther->szPage & (pOther->szPage-1))==0 && pOther->szPage>=512 );
assert( pOther->szExtra<512 );
if( pOther->szPage+pOther->szExtra != pCache->szPage+pCache->szExtra ){
pcache1FreePage(pPage);
pPage = 0;
}else{
pGroup->nCurrentPage -= (pOther->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 **)pPage->page.pExtra = 0;
pCache->apHash[h] = pPage;
}
fetch_out:
if( pPage && iKey>pCache->iMaxKey ){
pCache->iMaxKey = iKey;
}
pcache1LeaveMutex(pGroup);
return &pPage->page;
}
/*
** Implementation of the sqlite3_pcache.xUnpin method.
**
** Mark a page as unpinned (eligible for asynchronous recycling).
*/
static void pcache1Unpin(
sqlite3_pcache *p,
sqlite3_pcache_page *pPg,
int reuseUnlikely
){
PCache1 *pCache = (PCache1 *)p;
PgHdr1 *pPage = (PgHdr1 *)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,
sqlite3_pcache_page *pPg,
unsigned int iOld,
unsigned int iNew
){
PCache1 *pCache = (PCache1 *)p;
PgHdr1 *pPage = (PgHdr1 *)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);
assert( pGroup->nMaxPage >= pCache->nMax );
pGroup->nMaxPage -= pCache->nMax;
assert( pGroup->nMinPage >= pCache->nMin );
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_methods2 defaultMethods = {
1, /* iVersion */
0, /* pArg */
pcache1Init, /* xInit */
pcache1Shutdown, /* xShutdown */
pcache1Create, /* xCreate */
pcache1Cachesize, /* xCachesize */
pcache1Pagecount, /* xPagecount */
pcache1Fetch, /* xFetch */
pcache1Unpin, /* xUnpin */
pcache1Rekey, /* xRekey */
pcache1Truncate, /* xTruncate */
pcache1Destroy, /* xDestroy */
pcache1Shrink /* xShrink */
};
sqlite3_config(SQLITE_CONFIG_PCACHE2, &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(p->page.pBuf);
#ifdef SQLITE_PCACHE_SEPARATE_HEADER
nFree += sqlite3MemSize(p);
#endif
pcache1PinPage(p);
pcache1RemoveFromHash(p);
pcache1FreePage(p);
}
pcache1LeaveMutex(&pcache1.grp);
}
return nFree;
}
#endif /* SQLITE_ENABLE_MEMORY_MANAGEMENT */
#ifdef SQLITE_TEST