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+/*
+** 2008 August 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 that page cache.
+*/
+#include "sqliteInt.h"
+
+/*
+** A complete page cache is an instance of this structure.
+*/
+struct PCache {
+ PgHdr *pDirty, *pDirtyTail; /* List of dirty pages in LRU order */
+ PgHdr *pSynced; /* Last synced page in dirty page list */
+ int nRef; /* Number of referenced pages */
+ int nMax; /* Configured cache size */
+ int szPage; /* Size of every page in this cache */
+ int szExtra; /* Size of extra space for each page */
+ int bPurgeable; /* True if pages are on backing store */
+ int (*xStress)(void*,PgHdr*); /* Call to try make a page clean */
+ void *pStress; /* Argument to xStress */
+ sqlite3_pcache *pCache; /* Pluggable cache module */
+ PgHdr *pPage1; /* Reference to page 1 */
+};
+
+/*
+** Some of the assert() macros in this code are too expensive to run
+** even during normal debugging. Use them only rarely on long-running
+** tests. Enable the expensive asserts using the
+** -DSQLITE_ENABLE_EXPENSIVE_ASSERT=1 compile-time option.
+*/
+#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
+# define expensive_assert(X) assert(X)
+#else
+# define expensive_assert(X)
+#endif
+
+/********************************** Linked List Management ********************/
+
+#if !defined(NDEBUG) && defined(SQLITE_ENABLE_EXPENSIVE_ASSERT)
+/*
+** Check that the pCache->pSynced variable is set correctly. If it
+** is not, either fail an assert or return zero. Otherwise, return
+** non-zero. This is only used in debugging builds, as follows:
+**
+** expensive_assert( pcacheCheckSynced(pCache) );
+*/
+static int pcacheCheckSynced(PCache *pCache){
+ PgHdr *p;
+ for(p=pCache->pDirtyTail; p!=pCache->pSynced; p=p->pDirtyPrev){
+ assert( p->nRef || (p->flags&PGHDR_NEED_SYNC) );
+ }
+ return (p==0 || p->nRef || (p->flags&PGHDR_NEED_SYNC)==0);
+}
+#endif /* !NDEBUG && SQLITE_ENABLE_EXPENSIVE_ASSERT */
+
+/*
+** Remove page pPage from the list of dirty pages.
+*/
+static void pcacheRemoveFromDirtyList(PgHdr *pPage){
+ PCache *p = pPage->pCache;
+
+ assert( pPage->pDirtyNext || pPage==p->pDirtyTail );
+ assert( pPage->pDirtyPrev || pPage==p->pDirty );
+
+ /* Update the PCache1.pSynced variable if necessary. */
+ if( p->pSynced==pPage ){
+ PgHdr *pSynced = pPage->pDirtyPrev;
+ while( pSynced && (pSynced->flags&PGHDR_NEED_SYNC) ){
+ pSynced = pSynced->pDirtyPrev;
+ }
+ p->pSynced = pSynced;
+ }
+
+ if( pPage->pDirtyNext ){
+ pPage->pDirtyNext->pDirtyPrev = pPage->pDirtyPrev;
+ }else{
+ assert( pPage==p->pDirtyTail );
+ p->pDirtyTail = pPage->pDirtyPrev;
+ }
+ if( pPage->pDirtyPrev ){
+ pPage->pDirtyPrev->pDirtyNext = pPage->pDirtyNext;
+ }else{
+ assert( pPage==p->pDirty );
+ p->pDirty = pPage->pDirtyNext;
+ }
+ pPage->pDirtyNext = 0;
+ pPage->pDirtyPrev = 0;
+
+ expensive_assert( pcacheCheckSynced(p) );
+}
+
+/*
+** Add page pPage to the head of the dirty list (PCache1.pDirty is set to
+** pPage).
+*/
+static void pcacheAddToDirtyList(PgHdr *pPage){
+ PCache *p = pPage->pCache;
+
+ assert( pPage->pDirtyNext==0 && pPage->pDirtyPrev==0 && p->pDirty!=pPage );
+
+ pPage->pDirtyNext = p->pDirty;
+ if( pPage->pDirtyNext ){
+ assert( pPage->pDirtyNext->pDirtyPrev==0 );
+ pPage->pDirtyNext->pDirtyPrev = pPage;
+ }
+ p->pDirty = pPage;
+ if( !p->pDirtyTail ){
+ p->pDirtyTail = pPage;
+ }
+ if( !p->pSynced && 0==(pPage->flags&PGHDR_NEED_SYNC) ){
+ p->pSynced = pPage;
+ }
+ expensive_assert( pcacheCheckSynced(p) );
+}
+
+/*
+** Wrapper around the pluggable caches xUnpin method. If the cache is
+** being used for an in-memory database, this function is a no-op.
+*/
+static void pcacheUnpin(PgHdr *p){
+ PCache *pCache = p->pCache;
+ if( pCache->bPurgeable ){
+ if( p->pgno==1 ){
+ pCache->pPage1 = 0;
+ }
+ sqlite3GlobalConfig.pcache.xUnpin(pCache->pCache, p, 0);
+ }
+}
+
+/*************************************************** General Interfaces ******
+**
+** Initialize and shutdown the page cache subsystem. Neither of these
+** functions are threadsafe.
+*/
+int sqlite3PcacheInitialize(void){
+ if( sqlite3GlobalConfig.pcache.xInit==0 ){
+ /* IMPLEMENTATION-OF: R-26801-64137 If the xInit() method is NULL, then the
+ ** built-in default page cache is used instead of the application defined
+ ** page cache. */
+ sqlite3PCacheSetDefault();
+ }
+ return sqlite3GlobalConfig.pcache.xInit(sqlite3GlobalConfig.pcache.pArg);
+}
+void sqlite3PcacheShutdown(void){
+ if( sqlite3GlobalConfig.pcache.xShutdown ){
+ /* IMPLEMENTATION-OF: R-26000-56589 The xShutdown() method may be NULL. */
+ sqlite3GlobalConfig.pcache.xShutdown(sqlite3GlobalConfig.pcache.pArg);
+ }
+}
+
+/*
+** Return the size in bytes of a PCache object.
+*/
+int sqlite3PcacheSize(void){ return sizeof(PCache); }
+
+/*
+** Create a new PCache object. Storage space to hold the object
+** has already been allocated and is passed in as the p pointer.
+** The caller discovers how much space needs to be allocated by
+** calling sqlite3PcacheSize().
+*/
+void sqlite3PcacheOpen(
+ int szPage, /* Size of every page */
+ int szExtra, /* Extra space associated with each page */
+ int bPurgeable, /* True if pages are on backing store */
+ int (*xStress)(void*,PgHdr*),/* Call to try to make pages clean */
+ void *pStress, /* Argument to xStress */
+ PCache *p /* Preallocated space for the PCache */
+){
+ memset(p, 0, sizeof(PCache));
+ p->szPage = szPage;
+ p->szExtra = szExtra;
+ p->bPurgeable = bPurgeable;
+ p->xStress = xStress;
+ p->pStress = pStress;
+ p->nMax = 100;
+}
+
+/*
+** Change the page size for PCache object. The caller must ensure that there
+** are no outstanding page references when this function is called.
+*/
+void sqlite3PcacheSetPageSize(PCache *pCache, int szPage){
+ assert( pCache->nRef==0 && pCache->pDirty==0 );
+ if( pCache->pCache ){
+ sqlite3GlobalConfig.pcache.xDestroy(pCache->pCache);
+ pCache->pCache = 0;
+ pCache->pPage1 = 0;
+ }
+ pCache->szPage = szPage;
+}
+
+/*
+** Try to obtain a page from the cache.
+*/
+int 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 */
+){
+ PgHdr *pPage = 0;
+ int eCreate;
+
+ assert( pCache!=0 );
+ assert( createFlag==1 || createFlag==0 );
+ assert( pgno>0 );
+
+ /* If the pluggable cache (sqlite3_pcache*) has not been allocated,
+ ** allocate it now.
+ */
+ if( !pCache->pCache && createFlag ){
+ sqlite3_pcache *p;
+ int nByte;
+ nByte = pCache->szPage + pCache->szExtra + sizeof(PgHdr);
+ p = sqlite3GlobalConfig.pcache.xCreate(nByte, pCache->bPurgeable);
+ if( !p ){
+ return SQLITE_NOMEM;
+ }
+ sqlite3GlobalConfig.pcache.xCachesize(p, pCache->nMax);
+ pCache->pCache = p;
+ }
+
+ eCreate = createFlag * (1 + (!pCache->bPurgeable || !pCache->pDirty));
+ if( pCache->pCache ){
+ pPage = sqlite3GlobalConfig.pcache.xFetch(pCache->pCache, pgno, eCreate);
+ }
+
+ if( !pPage && eCreate==1 ){
+ PgHdr *pPg;
+
+ /* 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),
+ pCache->nMax);
+#endif
+ rc = pCache->xStress(pCache->pStress, pPg);
+ if( rc!=SQLITE_OK && rc!=SQLITE_BUSY ){
+ return rc;
+ }
+ }
+
+ pPage = sqlite3GlobalConfig.pcache.xFetch(pCache->pCache, pgno, 2);
+ }
+
+ if( pPage ){
+ if( !pPage->pData ){
+ memset(pPage, 0, sizeof(PgHdr));
+ pPage->pData = (void *)&pPage[1];
+ pPage->pExtra = (void*)&((char *)pPage->pData)[pCache->szPage];
+ memset(pPage->pExtra, 0, pCache->szExtra);
+ pPage->pCache = pCache;
+ pPage->pgno = pgno;
+ }
+ assert( pPage->pCache==pCache );
+ assert( pPage->pgno==pgno );
+ assert( pPage->pData==(void *)&pPage[1] );
+ assert( pPage->pExtra==(void *)&((char *)&pPage[1])[pCache->szPage] );
+
+ if( 0==pPage->nRef ){
+ pCache->nRef++;
+ }
+ pPage->nRef++;
+ if( pgno==1 ){
+ pCache->pPage1 = pPage;
+ }
+ }
+ *ppPage = pPage;
+ return (pPage==0 && eCreate) ? SQLITE_NOMEM : SQLITE_OK;
+}
+
+/*
+** Decrement the reference count on a page. If the page is clean and the
+** reference count drops to 0, then it is made elible for recycling.
+*/
+void sqlite3PcacheRelease(PgHdr *p){
+ assert( p->nRef>0 );
+ p->nRef--;
+ if( p->nRef==0 ){
+ PCache *pCache = p->pCache;
+ pCache->nRef--;
+ if( (p->flags&PGHDR_DIRTY)==0 ){
+ pcacheUnpin(p);
+ }else{
+ /* Move the page to the head of the dirty list. */
+ pcacheRemoveFromDirtyList(p);
+ pcacheAddToDirtyList(p);
+ }
+ }
+}
+
+/*
+** Increase the reference count of a supplied page by 1.
+*/
+void sqlite3PcacheRef(PgHdr *p){
+ assert(p->nRef>0);
+ p->nRef++;
+}
+
+/*
+** Drop a page from the cache. There must be exactly one reference to the
+** page. This function deletes that reference, so after it returns the
+** page pointed to by p is invalid.
+*/
+void sqlite3PcacheDrop(PgHdr *p){
+ PCache *pCache;
+ assert( p->nRef==1 );
+ if( p->flags&PGHDR_DIRTY ){
+ pcacheRemoveFromDirtyList(p);
+ }
+ pCache = p->pCache;
+ pCache->nRef--;
+ if( p->pgno==1 ){
+ pCache->pPage1 = 0;
+ }
+ sqlite3GlobalConfig.pcache.xUnpin(pCache->pCache, p, 1);
+}
+
+/*
+** Make sure the page is marked as dirty. If it isn't dirty already,
+** make it so.
+*/
+void sqlite3PcacheMakeDirty(PgHdr *p){
+ p->flags &= ~PGHDR_DONT_WRITE;
+ assert( p->nRef>0 );
+ if( 0==(p->flags & PGHDR_DIRTY) ){
+ p->flags |= PGHDR_DIRTY;
+ pcacheAddToDirtyList( p);
+ }
+}
+
+/*
+** Make sure the page is marked as clean. If it isn't clean already,
+** make it so.
+*/
+void sqlite3PcacheMakeClean(PgHdr *p){
+ if( (p->flags & PGHDR_DIRTY) ){
+ pcacheRemoveFromDirtyList(p);
+ p->flags &= ~(PGHDR_DIRTY|PGHDR_NEED_SYNC);
+ if( p->nRef==0 ){
+ pcacheUnpin(p);
+ }
+ }
+}
+
+/*
+** Make every page in the cache clean.
+*/
+void sqlite3PcacheCleanAll(PCache *pCache){
+ PgHdr *p;
+ while( (p = pCache->pDirty)!=0 ){
+ sqlite3PcacheMakeClean(p);
+ }
+}
+
+/*
+** Clear the PGHDR_NEED_SYNC flag from all dirty pages.
+*/
+void sqlite3PcacheClearSyncFlags(PCache *pCache){
+ PgHdr *p;
+ for(p=pCache->pDirty; p; p=p->pDirtyNext){
+ p->flags &= ~PGHDR_NEED_SYNC;
+ }
+ pCache->pSynced = pCache->pDirtyTail;
+}
+
+/*
+** Change the page number of page p to newPgno.
+*/
+void sqlite3PcacheMove(PgHdr *p, Pgno newPgno){
+ PCache *pCache = p->pCache;
+ assert( p->nRef>0 );
+ assert( newPgno>0 );
+ sqlite3GlobalConfig.pcache.xRekey(pCache->pCache, p, p->pgno, newPgno);
+ p->pgno = newPgno;
+ if( (p->flags&PGHDR_DIRTY) && (p->flags&PGHDR_NEED_SYNC) ){
+ pcacheRemoveFromDirtyList(p);
+ pcacheAddToDirtyList(p);
+ }
+}
+
+/*
+** Drop every cache entry whose page number is greater than "pgno". The
+** caller must ensure that there are no outstanding references to any pages
+** other than page 1 with a page number greater than pgno.
+**
+** If there is a reference to page 1 and the pgno parameter passed to this
+** function is 0, then the data area associated with page 1 is zeroed, but
+** the page object is not dropped.
+*/
+void sqlite3PcacheTruncate(PCache *pCache, Pgno pgno){
+ if( pCache->pCache ){
+ PgHdr *p;
+ PgHdr *pNext;
+ for(p=pCache->pDirty; p; p=pNext){
+ pNext = p->pDirtyNext;
+ /* This routine never gets call with a positive pgno except right
+ ** after sqlite3PcacheCleanAll(). So if there are dirty pages,
+ ** it must be that pgno==0.
+ */
+ assert( p->pgno>0 );
+ if( ALWAYS(p->pgno>pgno) ){
+ assert( p->flags&PGHDR_DIRTY );
+ sqlite3PcacheMakeClean(p);
+ }
+ }
+ if( pgno==0 && pCache->pPage1 ){
+ memset(pCache->pPage1->pData, 0, pCache->szPage);
+ pgno = 1;
+ }
+ sqlite3GlobalConfig.pcache.xTruncate(pCache->pCache, pgno+1);
+ }
+}
+
+/*
+** Close a cache.
+*/
+void sqlite3PcacheClose(PCache *pCache){
+ if( pCache->pCache ){
+ sqlite3GlobalConfig.pcache.xDestroy(pCache->pCache);
+ }
+}
+
+/*
+** Discard the contents of the cache.
+*/
+void sqlite3PcacheClear(PCache *pCache){
+ sqlite3PcacheTruncate(pCache, 0);
+}
+
+/*
+** Merge two lists of pages connected by pDirty and in pgno order.
+** Do not both fixing the pDirtyPrev pointers.
+*/
+static PgHdr *pcacheMergeDirtyList(PgHdr *pA, PgHdr *pB){
+ PgHdr result, *pTail;
+ pTail = &result;
+ while( pA && pB ){
+ if( pA->pgno<pB->pgno ){
+ pTail->pDirty = pA;
+ pTail = pA;
+ pA = pA->pDirty;
+ }else{
+ pTail->pDirty = pB;
+ pTail = pB;
+ pB = pB->pDirty;
+ }
+ }
+ if( pA ){
+ pTail->pDirty = pA;
+ }else if( pB ){
+ pTail->pDirty = pB;
+ }else{
+ pTail->pDirty = 0;
+ }
+ return result.pDirty;
+}
+
+/*
+** Sort the list of pages in accending order by pgno. Pages are
+** connected by pDirty pointers. The pDirtyPrev pointers are
+** corrupted by this sort.
+**
+** Since there cannot be more than 2^31 distinct pages in a database,
+** there cannot be more than 31 buckets required by the merge sorter.
+** One extra bucket is added to catch overflow in case something
+** ever changes to make the previous sentence incorrect.
+*/
+#define N_SORT_BUCKET 32
+static PgHdr *pcacheSortDirtyList(PgHdr *pIn){
+ PgHdr *a[N_SORT_BUCKET], *p;
+ int i;
+ memset(a, 0, sizeof(a));
+ while( pIn ){
+ p = pIn;
+ pIn = p->pDirty;
+ p->pDirty = 0;
+ for(i=0; ALWAYS(i<N_SORT_BUCKET-1); i++){
+ if( a[i]==0 ){
+ a[i] = p;
+ break;
+ }else{
+ p = pcacheMergeDirtyList(a[i], p);
+ a[i] = 0;
+ }
+ }
+ if( NEVER(i==N_SORT_BUCKET-1) ){
+ /* To get here, there need to be 2^(N_SORT_BUCKET) elements in
+ ** the input list. But that is impossible.
+ */
+ a[i] = pcacheMergeDirtyList(a[i], p);
+ }
+ }
+ p = a[0];
+ for(i=1; i<N_SORT_BUCKET; i++){
+ p = pcacheMergeDirtyList(p, a[i]);
+ }
+ return p;
+}
+
+/*
+** Return a list of all dirty pages in the cache, sorted by page number.
+*/
+PgHdr *sqlite3PcacheDirtyList(PCache *pCache){
+ PgHdr *p;
+ for(p=pCache->pDirty; p; p=p->pDirtyNext){
+ p->pDirty = p->pDirtyNext;
+ }
+ return pcacheSortDirtyList(pCache->pDirty);
+}
+
+/*
+** Return the total number of referenced pages held by the cache.
+*/
+int sqlite3PcacheRefCount(PCache *pCache){
+ return pCache->nRef;
+}
+
+/*
+** Return the number of references to the page supplied as an argument.
+*/
+int sqlite3PcachePageRefcount(PgHdr *p){
+ return p->nRef;
+}
+
+/*
+** Return the total number of pages in the cache.
+*/
+int sqlite3PcachePagecount(PCache *pCache){
+ int nPage = 0;
+ if( pCache->pCache ){
+ nPage = sqlite3GlobalConfig.pcache.xPagecount(pCache->pCache);
+ }
+ return nPage;
+}
+
+#ifdef SQLITE_TEST
+/*
+** Get the suggested cache-size value.
+*/
+int sqlite3PcacheGetCachesize(PCache *pCache){
+ return pCache->nMax;
+}
+#endif
+
+/*
+** Set the suggested cache-size value.
+*/
+void sqlite3PcacheSetCachesize(PCache *pCache, int mxPage){
+ pCache->nMax = mxPage;
+ if( pCache->pCache ){
+ sqlite3GlobalConfig.pcache.xCachesize(pCache->pCache, mxPage);
+ }
+}
+
+#if defined(SQLITE_CHECK_PAGES) || defined(SQLITE_DEBUG)
+/*
+** For all dirty pages currently in the cache, invoke the specified
+** callback. This is only used if the SQLITE_CHECK_PAGES macro is
+** defined.
+*/
+void sqlite3PcacheIterateDirty(PCache *pCache, void (*xIter)(PgHdr *)){
+ PgHdr *pDirty;
+ for(pDirty=pCache->pDirty; pDirty; pDirty=pDirty->pDirtyNext){
+ xIter(pDirty);
+ }
+}
+#endif
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