SQLite

/*
** 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; i<db->nDb; 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, ...){
  va_list ap;
  int rc;

/*
** 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:
**
**    OFF       sqlite3OsSync() is never called.  This is the default

int sqlite3PagerReadFileheader(Pager*, int, unsigned char*);

/* 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*);
i64 sqlite3PagerJournalSizeLimit(Pager *, i64);
sqlite3_backup **sqlite3PagerBackupPtr(Pager*);

void sqlite3PcacheSetCachesize(PCache *pCache, int mxPage){
  pCache->szCache = mxPage;
  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
** defined.
*/

** the total number of pages cached by purgeable pager-caches to the sum
** of the suggested cache-sizes.
*/
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

#ifdef SQLITE_TEST

  }
  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);
    sqlite3_mutex_enter(pcache1.mutex);
    sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_OVERFLOW, -nFreed);
    sqlite3_mutex_leave(pcache1.mutex);
    sqlite3_free(p);
  }
  return nFreed;
}

#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
/*
** Return the size of a pcache allocation
*/
static int pcache1MemSize(void *p){

    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;

    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

    }
    returnSingleInt(pParse, "wal_autocheckpoint", 
       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 ){
    static const char *const azLockName[] = {
      "unlocked", "shared", "reserved", "pending", "exclusive"

** of heap memory by deallocating non-essential memory allocations
** held by the database library.   Memory used to cache database
** 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.
** ^SQLite strives to keep heap memory utilization below the soft heap
** limit by reducing the number of pages held in the page cache

**
** [[the xDestroy() page cache method]]
** ^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;
  int (*xInit)(void*);
  void (*xShutdown)(void*);
  sqlite3_pcache *(*xCreate)(int szPage, int szExtra, int bPurgeable);
  void (*xCachesize)(sqlite3_pcache*, int nCachesize);
  int (*xPagecount)(sqlite3_pcache*);
  sqlite3_pcache_page *(*xFetch)(sqlite3_pcache*, unsigned key, int createFlag);
  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
** retained in the header file for backwards compatibility only.
*/

  }
  amt = sqlite3_release_memory(N);
  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
** is returned.
*/

     { "sqlite3_step",                  test_step          ,0 },
     { "sqlite3_sql",                   test_sql           ,0 },
     { "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},
     { "sqlite3_enable_load_extension", test_enable_load,        0},
     { "sqlite3_extended_result_codes", test_extended_result_codes, 0},

# 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