Index: src/main.c ================================================================== --- src/main.c +++ src/main.c @@ -527,10 +527,28 @@ ** Return the mutex associated with a database connection. */ sqlite3_mutex *sqlite3_db_mutex(sqlite3 *db){ return db->mutex; } + +/* +** Free up as much memory as we can from the given database +** connection. +*/ +int sqlite3_db_release_memory(sqlite3 *db){ + int i; + sqlite3BtreeEnterAll(db); + for(i=0; inDb; i++){ + Btree *pBt = db->aDb[i].pBt; + if( pBt ){ + Pager *pPager = sqlite3BtreePager(pBt); + sqlite3PagerShrink(pPager); + } + } + sqlite3BtreeLeaveAll(db); + return SQLITE_OK; +} /* ** Configuration settings for an individual database connection */ int sqlite3_db_config(sqlite3 *db, int op, ...){ Index: src/pager.c ================================================================== --- src/pager.c +++ src/pager.c @@ -3291,10 +3291,17 @@ ** Change the maximum number of in-memory pages that are allowed. */ void sqlite3PagerSetCachesize(Pager *pPager, int mxPage){ sqlite3PcacheSetCachesize(pPager->pPCache, mxPage); } + +/* +** Free as much memory as possible from the pager. +*/ +void sqlite3PagerShrink(Pager *pPager){ + sqlite3PcacheShrink(pPager->pPCache); +} /* ** Adjust the robustness of the database to damage due to OS crashes ** or power failures by changing the number of syncs()s when writing ** the rollback journal. There are three levels: Index: src/pager.h ================================================================== --- src/pager.h +++ src/pager.h @@ -101,10 +101,11 @@ /* Functions used to configure a Pager object. */ void sqlite3PagerSetBusyhandler(Pager*, int(*)(void *), void *); int sqlite3PagerSetPagesize(Pager*, u32*, int); int sqlite3PagerMaxPageCount(Pager*, int); void sqlite3PagerSetCachesize(Pager*, int); +void sqlite3PagerShrink(Pager*); void sqlite3PagerSetSafetyLevel(Pager*,int,int,int); int sqlite3PagerLockingMode(Pager *, int); int sqlite3PagerSetJournalMode(Pager *, int); int sqlite3PagerGetJournalMode(Pager*); int sqlite3PagerOkToChangeJournalMode(Pager*); Index: src/pcache.c ================================================================== --- src/pcache.c +++ src/pcache.c @@ -592,10 +592,19 @@ if( pCache->pCache ){ sqlite3GlobalConfig.pcache2.xCachesize(pCache->pCache, numberOfCachePages(pCache)); } } + +/* +** Free up as much memory as possible from the page cache. +*/ +void sqlite3PcacheShrink(PCache *pCache){ + if( pCache->pCache ){ + sqlite3GlobalConfig.pcache2.xShrink(pCache->pCache); + } +} #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 Index: src/pcache.h ================================================================== --- src/pcache.h +++ src/pcache.h @@ -139,10 +139,13 @@ */ void sqlite3PcacheSetCachesize(PCache *, int); #ifdef SQLITE_TEST int sqlite3PcacheGetCachesize(PCache *); #endif + +/* Free up as much memory as possible from the page cache */ +void sqlite3PcacheShrink(PCache*); #ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT /* Try to return memory used by the pcache module to the main memory heap */ int sqlite3PcacheReleaseMemory(int); #endif Index: src/pcache1.c ================================================================== --- src/pcache1.c +++ src/pcache1.c @@ -225,12 +225,13 @@ } /* ** Free an allocated buffer obtained from pcache1Alloc(). */ -static void pcache1Free(void *p){ - if( p==0 ) return; +static int pcache1Free(void *p){ + int nFreed = 0; + if( p==0 ) return 0; if( p>=pcache1.pStart && pn90pct = 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){ @@ -933,11 +953,12 @@ pcache1Pagecount, /* xPagecount */ pcache1Fetch, /* xFetch */ pcache1Unpin, /* xUnpin */ pcache1Rekey, /* xRekey */ pcache1Truncate, /* xTruncate */ - pcache1Destroy /* xDestroy */ + pcache1Destroy, /* xDestroy */ + pcache1Shrink /* xShrink */ }; sqlite3_config(SQLITE_CONFIG_PCACHE2, &defaultMethods); } #ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT Index: src/pragma.c ================================================================== --- src/pragma.c +++ src/pragma.c @@ -1436,10 +1436,20 @@ db->xWalCallback==sqlite3WalDefaultHook ? SQLITE_PTR_TO_INT(db->pWalArg) : 0); }else #endif + /* + ** PRAGMA shrink_memory + ** + ** This pragma attempts to free as much memory as possible from the + ** current database connection. + */ + if( sqlite3StrICmp(zLeft, "shrink_memory")==0 ){ + sqlite3_db_release_memory(db); + }else + #if defined(SQLITE_DEBUG) || defined(SQLITE_TEST) /* ** Report the current state of file logs for all databases */ if( sqlite3StrICmp(zLeft, "lock_status")==0 ){ Index: src/sqlite.h.in ================================================================== --- src/sqlite.h.in +++ src/sqlite.h.in @@ -4527,13 +4527,28 @@ ** pages to improve performance is an example of non-essential memory. ** ^sqlite3_release_memory() returns the number of bytes actually freed, ** which might be more or less than the amount requested. ** ^The sqlite3_release_memory() routine is a no-op returning zero ** if SQLite is not compiled with [SQLITE_ENABLE_MEMORY_MANAGEMENT]. +** +** See also: [sqlite3_db_release_memory()] */ int sqlite3_release_memory(int); +/* +** CAPI3REF: Free Memory Used By A Database Connection +** +** ^The sqlite3_db_shrink(D) interface attempts to free as much heap +** memory as possible from database connection D. Unlike the +** [sqlite3_release_memory()] interface, this interface is effect even +** when then [SQLITE_ENABLE_MEMORY_MANAGEMENT] compile-time option is +** omitted. +** +** See also: [sqlite3_release_memory()] +*/ +int sqlite3_db_release_memory(sqlite3*); + /* ** CAPI3REF: Impose A Limit On Heap Size ** ** ^The sqlite3_soft_heap_limit64() interface sets and/or queries the ** soft limit on the amount of heap memory that may be allocated by SQLite. @@ -6104,10 +6119,16 @@ ** ^The xDestroy() method is used to delete a cache allocated by xCreate(). ** All resources associated with the specified cache should be freed. ^After ** calling the xDestroy() method, SQLite considers the [sqlite3_pcache*] ** handle invalid, and will not use it with any other sqlite3_pcache_methods ** functions. +** +** [[the xShrink() page cache method]] +** ^SQLite invokes the xShrink() method when it wants the page cache to +** free up as much of heap memory as possible. The page cache implementation +** is not obligated to free any memory, but well-behaved implementions should +** do their best. */ typedef struct sqlite3_pcache_methods2 sqlite3_pcache_methods2; struct sqlite3_pcache_methods2 { int iVersion; void *pArg; @@ -6120,10 +6141,11 @@ void (*xUnpin)(sqlite3_pcache*, sqlite3_pcache_page*, int discard); void (*xRekey)(sqlite3_pcache*, sqlite3_pcache_page*, unsigned oldKey, unsigned newKey); void (*xTruncate)(sqlite3_pcache*, unsigned iLimit); void (*xDestroy)(sqlite3_pcache*); + void (*xShrink)(sqlite3_pcache*); }; /* ** This is the obsolete pcache_methods object that has now been replaced ** by sqlite3_pcache_methods2. This object is not used by SQLite. It is Index: src/test1.c ================================================================== --- src/test1.c +++ src/test1.c @@ -4591,10 +4591,35 @@ Tcl_SetObjResult(interp, Tcl_NewIntObj(amt)); #endif return TCL_OK; } + +/* +** Usage: sqlite3_db_release_memory DB +** +** Attempt to release memory currently held by database DB. Return the +** result code (which in the current implementation is always zero). +*/ +static int test_db_release_memory( + void * clientData, + Tcl_Interp *interp, + int objc, + Tcl_Obj *CONST objv[] +){ + sqlite3 *db; + int rc; + if( objc!=2 ){ + Tcl_WrongNumArgs(interp, 1, objv, "DB"); + return TCL_ERROR; + } + if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR; + rc = sqlite3_db_release_memory(db); + Tcl_SetObjResult(interp, Tcl_NewIntObj(rc)); + return TCL_OK; +} + /* ** Usage: sqlite3_soft_heap_limit ?N? ** ** Query or set the soft heap limit for the current thread. The ** limit is only changed if the N is present. The previous limit @@ -5913,10 +5938,11 @@ { "sqlite3_next_stmt", test_next_stmt ,0 }, { "sqlite3_stmt_readonly", test_stmt_readonly ,0 }, { "uses_stmt_journal", uses_stmt_journal ,0 }, { "sqlite3_release_memory", test_release_memory, 0}, + { "sqlite3_db_release_memory", test_db_release_memory, 0}, { "sqlite3_soft_heap_limit", test_soft_heap_limit, 0}, { "sqlite3_thread_cleanup", test_thread_cleanup, 0}, { "sqlite3_pager_refcounts", test_pager_refcounts, 0}, { "sqlite3_load_extension", test_load_extension, 0}, ADDED test/shrink.test Index: test/shrink.test ================================================================== --- test/shrink.test +++ test/shrink.test @@ -0,0 +1,42 @@ +# 2011 November 16 +# +# 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 contains test cases for sqlite3_db_release_memory and +# the PRAGMA shrink_memory statement. +# + +set testdir [file dirname $argv0] +source $testdir/tester.tcl + +unset -nocomplain baseline +do_test shrink-1.1 { + db eval { + CREATE TABLE t1(x,y); + INSERT INTO t1 VALUES(randomblob(1000000),1); + } + set ::baseline sqlite3_memory_used + sqlite3_db_release_memory db + expr {$::baseline > [sqlite3_memory_used]+500000} +} {1} +do_test shrink-1.2 { + set baseline [sqlite3_memory_used] + db eval { + UPDATE t1 SET y=y+1; + } + expr {$::baseline+500000 < [sqlite3_memory_used]} +} {1} +do_test shrink-1.3 { + set baseline [sqlite3_memory_used] + db eval {PRAGMA shrink_memory} + expr {$::baseline > [sqlite3_memory_used]+500000} +} {1} + +finish_test