/*
** 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.
**
** @(#) $Id: pcache1.c,v 1.4 2008/11/24 20:05:39 shane Exp $
*/
#include "sqliteInt.h"
typedef struct PCache1 PCache1;
typedef struct PgHdr1 PgHdr1;
typedef struct PgFreeslot PgFreeslot;
/* 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 global mutex must be held when accessing nMax.
*/
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 */
/* Hash table of all pages. The following variables may only be accessed
** when the accessor is holding the global mutex (see pcache1EnterMutex()
** and pcache1LeaveMutex()).
*/
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. A buffer of PgHdr1.pCache->szPage bytes is allocated
** directly after the 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 {
sqlite3_mutex *mutex; /* static mutex MUTEX_STATIC_LRU */
int nMaxPage; /* Sum of nMaxPage for purgeable caches */
int nMinPage; /* Sum of nMinPage for purgeable caches */
int nCurrentPage; /* Number of purgeable pages allocated */
PgHdr1 *pLruHead, *pLruTail; /* LRU list of unpinned pages */
/* Variables related to SQLITE_CONFIG_PAGECACHE settings. */
int szSlot; /* Size of each free slot */
void *pStart, *pEnd; /* Bounds of pagecache malloc range */
PgFreeslot *pFree; /* Free page blocks */
} 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 after 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(X))==X );
*/
#define PGHDR1_TO_PAGE(p) (void *)(&((unsigned char *)p)[sizeof(PgHdr1)])
#define PAGE_TO_PGHDR1(p) (PgHdr1 *)(&((unsigned char *)p)[-1*(int)sizeof(PgHdr1)])
/*
** Macros to enter and leave the global LRU mutex.
*/
#define pcache1EnterMutex() sqlite3_mutex_enter(pcache1.mutex)
#define pcache1LeaveMutex() sqlite3_mutex_leave(pcache1.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.
*/
void sqlite3PCacheBufferSetup(void *pBuf, int sz, int n){
PgFreeslot *p;
sz &= ~7;
pcache1.szSlot = sz;
pcache1.pStart = pBuf;
pcache1.pFree = 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().
*/
static void *pcache1Alloc(int nByte){
void *p;
assert( sqlite3_mutex_held(pcache1.mutex) );
if( nByte<=pcache1.szSlot && pcache1.pFree ){
p = (PgHdr1 *)pcache1.pFree;
pcache1.pFree = pcache1.pFree->pNext;
sqlite3StatusSet(SQLITE_STATUS_PAGECACHE_SIZE, nByte);
sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_USED, 1);
}else{
/* Allocate a new buffer using sqlite3Malloc. Before doing so, exit the
** global pcache mutex and unlock the pager-cache object pCache. This is
** so that if the attempt to allocate a new buffer causes the the
** configured soft-heap-limit to be breached, it will be possible to
** reclaim memory from this pager-cache.
*/
pcache1LeaveMutex();
p = sqlite3Malloc(nByte);
pcache1EnterMutex();
if( p ){
int sz = sqlite3MallocSize(p);
sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_OVERFLOW, sz);
}
}
return p;
}
/*
** Free an allocated buffer obtained from pcache1Alloc().
*/
static void pcache1Free(void *p){
assert( sqlite3_mutex_held(pcache1.mutex) );
if( p==0 ) return;
if( p>=pcache1.pStart && p<pcache1.pEnd ){
PgFreeslot *pSlot;
sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_USED, -1);
pSlot = (PgFreeslot*)p;
pSlot->pNext = pcache1.pFree;
pcache1.pFree = pSlot;
}else{
int iSize = sqlite3MallocSize(p);
sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_OVERFLOW, -iSize);
sqlite3_free(p);
}
}
/*
** Allocate a new page object initially associated with cache pCache.
*/
static PgHdr1 *pcache1AllocPage(PCache1 *pCache){
int nByte = sizeof(PgHdr1) + pCache->szPage;
PgHdr1 *p = (PgHdr1 *)pcache1Alloc(nByte);
if( p ){
memset(p, 0, nByte);
if( pCache->bPurgeable ){
pcache1.nCurrentPage++;
}
}
return p;
}
/*
** Free a page object allocated by pcache1AllocPage().
*/
static void pcache1FreePage(PgHdr1 *p){
if( p ){
if( p->pCache->bPurgeable ){
pcache1.nCurrentPage--;
}
pcache1Free(p);
}
}
/*
** 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){
void *p;
pcache1EnterMutex();
p = pcache1Alloc(sz);
pcache1LeaveMutex();
return p;
}
/*
** Free an allocated buffer obtained from sqlite3PageMalloc().
*/
void sqlite3PageFree(void *p){
pcache1EnterMutex();
pcache1Free(p);
pcache1LeaveMutex();
}
/******************************************************************************/
/******** General Implementation Functions ************************************/
/*
** This function is used to resize the hash table used by the cache passed
** as the first argument.
**
** The global 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(pcache1.mutex) );
nNew = p->nHash*2;
if( nNew<256 ){
nNew = 256;
}
pcache1LeaveMutex();
apNew = (PgHdr1 **)sqlite3_malloc(sizeof(PgHdr1 *)*nNew);
pcache1EnterMutex();
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) ){
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
** global LRU list, if is part of it. If pPage is not part of the global
** LRU list, then this function is a no-op.
**
** The global mutex must be held when this function is called.
*/
static void pcache1PinPage(PgHdr1 *pPage){
assert( sqlite3_mutex_held(pcache1.mutex) );
if( pPage && (pPage->pLruNext || pPage==pcache1.pLruTail) ){
if( pPage->pLruPrev ){
pPage->pLruPrev->pLruNext = pPage->pLruNext;
}
if( pPage->pLruNext ){
pPage->pLruNext->pLruPrev = pPage->pLruPrev;
}
if( pcache1.pLruHead==pPage ){
pcache1.pLruHead = pPage->pLruNext;
}
if( pcache1.pLruTail==pPage ){
pcache1.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 global mutex must be held when this function is called.
*/
static void pcache1RemoveFromHash(PgHdr1 *pPage){
unsigned int h;
PCache1 *pCache = pPage->pCache;
PgHdr1 **pp;
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 pcache.nMaxPage pages allocated, try
** to recycle pages to reduce the number allocated to pcache.nMaxPage.
*/
static void pcache1EnforceMaxPage(void){
assert( sqlite3_mutex_held(pcache1.mutex) );
while( pcache1.nCurrentPage>pcache1.nMaxPage && pcache1.pLruTail ){
PgHdr1 *p = pcache1.pLruTail;
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 global mutex must be held when this function is called.
*/
static void pcache1TruncateUnsafe(
PCache1 *pCache,
unsigned int iLimit
){
unsigned int h;
assert( sqlite3_mutex_held(pcache1.mutex) );
for(h=0; h<pCache->nHash; h++){
PgHdr1 **pp = &pCache->apHash[h];
PgHdr1 *pPage;
while( (pPage = *pp) ){
if( pPage->iKey>=iLimit ){
pcache1PinPage(pPage);
*pp = pPage->pNext;
pcache1FreePage(pPage);
}else{
pp = &pPage->pNext;
}
}
}
}
/******************************************************************************/
/******** sqlite3_pcache Methods **********************************************/
/*
** Implementation of the sqlite3_pcache.xInit method.
*/
static int pcache1Init(void *NotUsed){
UNUSED_PARAMETER(NotUsed);
memset(&pcache1, 0, sizeof(pcache1));
if( sqlite3GlobalConfig.bCoreMutex ){
pcache1.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_LRU);
}
return SQLITE_OK;
}
/*
** Implementation of the sqlite3_pcache.xShutdown method.
*/
static void pcache1Shutdown(void *NotUsed){
UNUSED_PARAMETER(NotUsed);
/* no-op */
}
/*
** Implementation of the sqlite3_pcache.xCreate method.
**
** Allocate a new cache.
*/
static sqlite3_pcache *pcache1Create(int szPage, int bPurgeable){
PCache1 *pCache;
pCache = (PCache1 *)sqlite3_malloc(sizeof(PCache1));
if( pCache ){
memset(pCache, 0, sizeof(PCache1));
pCache->szPage = szPage;
pCache->bPurgeable = (bPurgeable ? 1 : 0);
if( bPurgeable ){
pCache->nMin = 10;
pcache1EnterMutex();
pcache1.nMinPage += pCache->nMin;
pcache1LeaveMutex();
}
}
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 ){
pcache1EnterMutex();
pcache1.nMaxPage += (nMax - pCache->nMax);
pCache->nMax = nMax;
pcache1EnforceMaxPage();
pcache1LeaveMutex();
}
}
/*
** Implementation of the sqlite3_pcache.xPagecount method.
*/
static int pcache1Pagecount(sqlite3_pcache *p){
int n;
pcache1EnterMutex();
n = ((PCache1 *)p)->nPage;
pcache1LeaveMutex();
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.
**
** 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, the cache is marked as purgeable and the page is
** not already in the cache, and if either of the following are true,
** return NULL:
**
** (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.
**
** 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,
**
** 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){
unsigned int nPinned;
PCache1 *pCache = (PCache1 *)p;
PgHdr1 *pPage = 0;
pcache1EnterMutex();
if( createFlag==1 ) sqlite3BeginBenignMalloc();
/* 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);
}
if( pPage || createFlag==0 ){
pcache1PinPage(pPage);
goto fetch_out;
}
/* Step 3 of header comment. */
nPinned = pCache->nPage - pCache->nRecyclable;
if( createFlag==1 && pCache->bPurgeable && (
nPinned>=(pcache1.nMaxPage+pCache->nMin-pcache1.nMinPage)
|| nPinned>=(pCache->nMax)
)){
goto fetch_out;
}
if( pCache->nPage>=pCache->nHash && pcache1ResizeHash(pCache) ){
goto fetch_out;
}
/* Step 4. Try to recycle a page buffer if appropriate. */
if( pCache->bPurgeable && pcache1.pLruTail && (
pCache->nPage>=pCache->nMax-1 || pcache1.nCurrentPage>=pcache1.nMaxPage
)){
pPage = pcache1.pLruTail;
pcache1RemoveFromHash(pPage);
pcache1PinPage(pPage);
if( pPage->pCache->szPage!=pCache->szPage ){
pcache1FreePage(pPage);
pPage = 0;
}else{
pcache1.nCurrentPage -= (pPage->pCache->bPurgeable - pCache->bPurgeable);
}
}
/* Step 5. If a usable page buffer has still not been found,
** attempt to allocate a new one.
*/
if( !pPage ){
pPage = pcache1AllocPage(pCache);
}
if( pPage ){
unsigned int h = iKey % pCache->nHash;
memset(pPage, 0, pCache->szPage + sizeof(PgHdr1));
pCache->nPage++;
pPage->iKey = iKey;
pPage->pNext = pCache->apHash[h];
pPage->pCache = pCache;
pCache->apHash[h] = pPage;
}
fetch_out:
if( createFlag==1 ) sqlite3EndBenignMalloc();
pcache1LeaveMutex();
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(pPg);
pcache1EnterMutex();
/* It is an error to call this function if the page is already
** part of the global LRU list.
*/
assert( pPage->pLruPrev==0 && pPage->pLruNext==0 );
assert( pcache1.pLruHead!=pPage && pcache1.pLruTail!=pPage );
if( reuseUnlikely || pcache1.nCurrentPage>pcache1.nMaxPage ){
pcache1RemoveFromHash(pPage);
pcache1FreePage(pPage);
}else{
/* Add the page to the global LRU list. Normally, the page is added to
** the head of the list (last page to be recycled). However, if the
** reuseUnlikely flag passed to this function is true, the page is added
** to the tail of the list (first page to be recycled).
*/
if( pcache1.pLruHead ){
pcache1.pLruHead->pLruPrev = pPage;
pPage->pLruNext = pcache1.pLruHead;
pcache1.pLruHead = pPage;
}else{
pcache1.pLruTail = pPage;
pcache1.pLruHead = pPage;
}
pCache->nRecyclable++;
}
pcache1LeaveMutex();
}
/*
** 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(pPg);
PgHdr1 **pp;
unsigned int h;
assert( pPage->iKey==iOld );
pcache1EnterMutex();
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;
pcache1LeaveMutex();
}
/*
** 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();
pcache1TruncateUnsafe(pCache, iLimit);
pcache1LeaveMutex();
}
/*
** Implementation of the sqlite3_pcache.xDestroy method.
**
** Destroy a cache allocated using pcache1Create().
*/
static void pcache1Destroy(sqlite3_pcache *p){
PCache1 *pCache = (PCache1 *)p;
pcache1EnterMutex();
pcache1TruncateUnsafe(pCache, 0);
pcache1.nMaxPage -= pCache->nMax;
pcache1.nMinPage -= pCache->nMin;
pcache1EnforceMaxPage();
pcache1LeaveMutex();
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 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;
if( pcache1.pStart==0 ){
PgHdr1 *p;
pcache1EnterMutex();
while( (nReq<0 || nFree<nReq) && (p=pcache1.pLruTail) ){
nFree += sqlite3MallocSize(p);
pcache1PinPage(p);
pcache1RemoveFromHash(p);
pcache1FreePage(p);
}
pcache1LeaveMutex();
}
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.pLruHead; p; p=p->pLruNext){
nRecyclable++;
}
*pnCurrent = pcache1.nCurrentPage;
*pnMax = pcache1.nMaxPage;
*pnMin = pcache1.nMinPage;
*pnRecyclable = nRecyclable;
}
#endif