SQLite

  /* 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 separateCache;             /* Use a new PGroup for each PCache */
  int nInitPage;                 /* Initial bulk allocation size */   
  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 global page cache memory */
  /* Above requires no mutex.  Use mutex below for variable that follow. */
  sqlite3_mutex *mutex;          /* Mutex for accessing the following: */
  PgFreeslot *pFree;             /* Free page blocks */

      p->pNext = pcache1.pFree;
      pcache1.pFree = p;
      pBuf = (void*)&((char*)pBuf)[sz];
    }
    pcache1.pEnd = pBuf;
  }
}

/*
** Try to initialize the pCache->pFree and pCache->pBulk fields.  Return
** true if pCache->pFree ends up containing one or more free pages.
*/
static int pcache1InitBulk(PCache1 *pCache){
  int szBulk;
  char *zBulk;
  if( pcache1.nInitPage==0 ) return 0;
  /* Do not bother with a bulk allocation if the cache size very small */
  if( pCache->nMax<3 ) return 0;
  sqlite3BeginBenignMalloc();
  if( pcache1.nInitPage>0 ){
    szBulk = pCache->szAlloc * pcache1.nInitPage;
  }else{
    szBulk = -1024*pcache1.nInitPage;
  }
  if( szBulk > pCache->szAlloc*pCache->nMax ){
    szBulk = pCache->szAlloc*pCache->nMax;
  }
  zBulk = pCache->pBulk = sqlite3Malloc( szBulk );
  sqlite3EndBenignMalloc();
  if( zBulk ){
    int nBulk = sqlite3MallocSize(zBulk)/pCache->szAlloc;
    int i;
    for(i=0; i<nBulk; i++){
      PgHdr1 *pX = (PgHdr1*)&zBulk[pCache->szPage];
      pX->page.pBuf = zBulk;
      pX->page.pExtra = &pX[1];
      pX->isBulkLocal = 1;
      pX->pNext = pCache->pFree;
      pCache->pFree = pX;
      zBulk += pCache->szAlloc;
    }
  }
  return pCache->pFree!=0;
}

/*
** 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().
**

** Allocate a new page object initially associated with cache pCache.
*/
static PgHdr1 *pcache1AllocPage(PCache1 *pCache){
  PgHdr1 *p = 0;
  void *pPg;

  assert( sqlite3_mutex_held(pCache->pGroup->mutex) );
  if( pCache->pFree || (pCache->nPage==0 && pcache1InitBulk(pCache)) ){
    p = pCache->pFree;
    pCache->pFree = p->pNext;
    p->pNext = 0;
  }else{
#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
    /* The group mutex must be released before pcache1Alloc() is called. This
    ** is because it might call sqlite3_release_memory(), which assumes that 

  if( freeFlag ) pcache1FreePage(pPage);
}

/*
** If there are currently more than nMaxPage pages allocated, try
** to recycle pages to reduce the number allocated to nMaxPage.
*/
static void pcache1EnforceMaxPage(PCache1 *pCache){
  PGroup *pGroup = pCache->pGroup;
  assert( sqlite3_mutex_held(pGroup->mutex) );
  while( pGroup->nCurrentPage>pGroup->nMaxPage && pGroup->pLruTail ){
    PgHdr1 *p = pGroup->pLruTail;
    assert( p->pCache->pGroup==pGroup );
    assert( p->isPinned==0 );
    pcache1PinPage(p);
    pcache1RemoveFromHash(p, 1);
  }
  if( pCache->nPage==0 && pCache->pBulk ){
    sqlite3_free(pCache->pBulk);
    pCache->pBulk = pCache->pFree = 0;
  }
}

/*
** 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.

#if SQLITE_THREADSAFE
  if( sqlite3GlobalConfig.bCoreMutex ){
    pcache1.grp.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_LRU);
    pcache1.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_PMEM);
  }
#endif
  if( pcache1.separateCache
   && sqlite3GlobalConfig.nPage!=0
   && sqlite3GlobalConfig.pPage==0
  ){
    pcache1.nInitPage = sqlite3GlobalConfig.nPage;
  }else{
    pcache1.nInitPage = 0;
  }
  pcache1.grp.mxPinned = 10;
  pcache1.isInit = 1;
  return SQLITE_OK;
}

/*
** Implementation of the sqlite3_pcache.xShutdown method.

    pcache1ResizeHash(pCache);
    if( bPurgeable ){
      pCache->nMin = 10;
      pGroup->nMinPage += pCache->nMin;
      pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage;
    }
    pcache1LeaveMutex(pGroup);






























    if( pCache->nHash==0 ){
      pcache1Destroy((sqlite3_pcache*)pCache);
      pCache = 0;
    }
  }
  return (sqlite3_pcache *)pCache;
}

  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(pCache);
    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(pCache);
    pGroup->nMaxPage = savedMaxPage;
    pcache1LeaveMutex(pGroup);
  }
}

/*
** Implementation of the sqlite3_pcache.xPagecount method. 

  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(pCache);
  pcache1LeaveMutex(pGroup);
  sqlite3_free(pCache->pBulk);
  sqlite3_free(pCache->apHash);
  sqlite3_free(pCache);
}

/*

  ** number of pages in the cache.  If N is negative, then the
  ** number of pages is adjusted so that the cache uses -N kibibytes
  ** of memory.
  */
  case PragTyp_CACHE_SIZE: {
    assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
    if( !zRight ){
      if( sqlite3ReadSchema(pParse) ) goto pragma_out;
      returnSingleInt(pParse, "cache_size", pDb->pSchema->cache_size);
    }else{
      int size = sqlite3Atoi(zRight);
      pDb->pSchema->cache_size = size;
      sqlite3BtreeSetCacheSize(pDb->pBt, pDb->pSchema->cache_size);
    }
    break;

  { /* zName:     */ "busy_timeout",
    /* ePragTyp:  */ PragTyp_BUSY_TIMEOUT,
    /* ePragFlag: */ 0,
    /* iArg:      */ 0 },
#if !defined(SQLITE_OMIT_PAGER_PRAGMAS)
  { /* zName:     */ "cache_size",
    /* ePragTyp:  */ PragTyp_CACHE_SIZE,
    /* ePragFlag: */ 0,
    /* iArg:      */ 0 },
#endif
#if !defined(SQLITE_OMIT_FLAG_PRAGMAS)
  { /* zName:     */ "cache_spill",
    /* ePragTyp:  */ PragTyp_FLAG,
    /* ePragFlag: */ 0,
    /* iArg:      */ SQLITE_CacheSpill },

ifcapable !memorymanage {
   finish_test
   return
}

sqlite3_soft_heap_limit 0
sqlite3 db test.db
db eval {PRAGMA cache_size=1}

do_test malloc5-1.1 {
  # Simplest possible test. Call sqlite3_release_memory when there is exactly
  # one unused page in a single pager cache. The page cannot be freed, as
  # it is dirty. So sqlite3_release_memory() returns 0.
  #
  execsql {
    PRAGMA auto_vacuum=OFF;
    BEGIN;
    CREATE TABLE abc(a, b, c);
  }
  sqlite3_release_memory
} {0}

do_test malloc5-1.2 {
  # Test that the transaction started in the above test is still active.
  # The lock on the database file should not have been upgraded (this was
  # not the case before version 3.6.2).
  #
  sqlite3 db2 test.db
  execsql {PRAGMA cache_size=2; SELECT * FROM sqlite_master } db2
} {}
do_test malloc5-1.3 {
  # Call [sqlite3_release_memory] when there is exactly one unused page 
  # in the cache belonging to db2.
  #
  set ::pgalloc [sqlite3_release_memory]

} {0}

# The sizes of memory allocations from system malloc() might vary,
# depending on the memory allocator algorithms used.  The following
# routine is designed to support answers that fall within a range
# of values while also supplying easy-to-understand "expected" values
# when errors occur.
#

  sqlite3_memory_highwater 1
  execsql {SELECT * FROM abc}
  set nMaxBytes [sqlite3_memory_highwater 1]
  puts -nonewline " (Highwater mark: $nMaxBytes) "
  expr $nMaxBytes > 1000000
} {1}
do_test malloc5-4.2 {
  db eval {PRAGMA cache_size=1}
  db cache flush
  sqlite3_release_memory
  sqlite3_soft_heap_limit 100000
  sqlite3_memory_highwater 1
  execsql {SELECT * FROM abc}
  set nMaxBytes [sqlite3_memory_highwater 1]
  puts -nonewline " (Highwater mark: $nMaxBytes) "

# This block of test-cases (malloc5-6.1.*) prepares two database files
# for the subsequent tests.
do_test malloc5-6.1.1 {
  sqlite3 db test.db
  execsql {
    PRAGMA page_size=1024;
    PRAGMA default_cache_size=2;
  }
  execsql {
    PRAGMA temp_store = memory;
    BEGIN;
    CREATE TABLE abc(a PRIMARY KEY, b, c);
    INSERT INTO abc VALUES(randstr(50,50), randstr(75,75), randstr(100,100));
    INSERT INTO abc 

        SELECT randstr(50,50), randstr(75,75), randstr(100,100) FROM abc;
    INSERT INTO abc 
        SELECT randstr(50,50), randstr(75,75), randstr(100,100) FROM abc;
    COMMIT;
  } 
  forcecopy test.db test2.db
  sqlite3 db2 test2.db
  db2 eval {PRAGMA cache_size=2}
  list \
    [expr ([file size test.db]/1024)>20] [expr ([file size test2.db]/1024)>20]
} {1 1}
do_test malloc5-6.1.2 {
  list [execsql {PRAGMA cache_size}] [execsql {PRAGMA cache_size} db2]
} {2 2}

do_test malloc5-6.2.1 {
  execsql {SELECT * FROM abc} db2
  execsql {SELECT * FROM abc} db
  expr [nPage db] + [nPage db2]
} {4}

do_test malloc5-6.2.2 {
  # If we now try to reclaim some memory, it should come from the db2 cache.
  sqlite3_release_memory 3000
  expr [nPage db] + [nPage db2]
} {4}
do_test malloc5-6.2.3 {
  # Access the db2 cache again, so that all the db2 pages have been used
  # more recently than all the db pages. Then try to reclaim 3000 bytes.
  # This time, 3 pages should be pulled from the db cache.
  execsql { SELECT * FROM abc } db2
  sqlite3_release_memory 3000
  expr [nPage db] + [nPage db2]
} {4}

do_test malloc5-6.3.1 {
  # Now open a transaction and update 2 pages in the db2 cache. Then
  # do a SELECT on the db cache so that all the db pages are more recently
  # used than the db2 pages. When we try to free memory, SQLite should
  # free the non-dirty db2 pages, then the db pages, then finally use
  # sync() to free up the dirty db2 pages. The only page that cannot be
  # freed is page1 of db2. Because there is an open transaction, the
  # btree layer holds a reference to page 1 in the db2 cache.
  execsql {
    BEGIN;
    UPDATE abc SET c = randstr(100,100) 
    WHERE rowid = 1 OR rowid = (SELECT max(rowid) FROM abc);
  } db2
  execsql { SELECT * FROM abc } db
  expr [nPage db] + [nPage db2]
} {4}
do_test malloc5-6.3.2 {
  # Try to release 7700 bytes. This should release all the 
  # non-dirty pages held by db2.
  sqlite3_release_memory [expr 7*1132]
  list [nPage db] [nPage db2]
} {1 3}
do_test malloc5-6.3.3 {
  # Try to release another 1000 bytes. This should come fromt the db
  # cache, since all three pages held by db2 are either in-use or diry.
  sqlite3_release_memory 1000
  list [nPage db] [nPage db2]
} {1 3}
do_test malloc5-6.3.4 {
  # Now release 9900 more (about 9 pages worth). This should expunge
  # the rest of the db cache. But the db2 cache remains intact, because
  # SQLite tries to avoid calling sync().
  if {$::tcl_platform(wordSize)==8} {
    sqlite3_release_memory 10500
  } else {
    sqlite3_release_memory 9900
  }
  list [nPage db] [nPage db2]
} {1 3}
do_test malloc5-6.3.5 {
  # But if we are really insistent, SQLite will consent to call sync()
  # if there is no other option. UPDATE: As of 3.6.2, SQLite will not
  # call sync() in this scenario. So no further memory can be reclaimed.
  sqlite3_release_memory 1000
  list [nPage db] [nPage db2]
} {1 3}
do_test malloc5-6.3.6 {
  # The referenced page (page 1 of the db2 cache) will not be freed no
  # matter how much memory we ask for:
  sqlite3_release_memory 31459
  list [nPage db] [nPage db2]
} {1 3}

db2 close

sqlite3_soft_heap_limit $::soft_limit
finish_test
catch {db close}

    CREATE TABLE t9(a, b, c);
  }
  pcache_stats
} {current 10 max 12 min 10 recyclable 0}

do_test pcache-1.5 {
  sqlite3 db2 test.db
  execsql "PRAGMA cache_size; PRAGMA cache_size=10" db2
  pcache_stats
} {current 11 max 22 min 20 recyclable 1}

do_test pcache-1.6.1 {
  execsql {
    BEGIN;
    SELECT * FROM sqlite_master;

} {0 0 0}

# Open up two database connections to separate files.
#
do_test pcache2-1.2 {
  forcedelete test.db test.db-journal
  sqlite3 db test.db
  db eval {PRAGMA cache_size=10; SELECT 1 FROM sqlite_master;}
  lindex [sqlite3_status SQLITE_STATUS_PAGECACHE_USED 0] 1
} {2}
do_test pcache2-1.3 {
  forcedelete test2.db test2.db-journal
  sqlite3 db2 test2.db
  db2 eval {PRAGMA cache_size=50; SELECT 1 FROM sqlite_master;}
  lindex [sqlite3_status SQLITE_STATUS_PAGECACHE_USED 0] 1
} {4}


# Make lots of changes on the first connection.  Verify that the
# page cache usage does not grow to consume the page space set aside
# for the second connection.

  FLAG: NeedSchema
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: journal_size_limit
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: cache_size

  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: mmap_size
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: auto_vacuum
  FLAG: NeedSchema