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Overview
Comment:Add an API to support custom page cache implementations. (CVS 5899)
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1: 47866d6708e9b69e367937fd85f93580fd025447
User & Date: danielk1977 2008-11-13 14:28:29
Context
2008-11-13
14:42
Update mksqlite3c.tcl to include new file pcache1.c. (CVS 5900) check-in: 00442e0f user: danielk1977 tags: trunk
14:28
Add an API to support custom page cache implementations. (CVS 5899) check-in: 47866d67 user: danielk1977 tags: trunk
2008-11-12
18:21
Avoid some buffer overreads detected by valgrind while running corruptC.test. (CVS 5898) check-in: faa6bd7b user: danielk1977 tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to Makefile.in.

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        btree.lo build.lo callback.lo complete.lo date.lo \
        delete.lo expr.lo fault.lo func.lo global.lo \
        hash.lo journal.lo insert.lo legacy.lo loadext.lo \
        main.lo malloc.lo mem0.lo mem1.lo mem2.lo mem3.lo mem5.lo \
        memjournal.lo \
        mutex.lo mutex_noop.lo mutex_os2.lo mutex_unix.lo mutex_w32.lo \
        opcodes.lo os.lo os_unix.lo os_win.lo os_os2.lo \
        pager.lo parse.lo pcache.lo pragma.lo prepare.lo printf.lo random.lo \
        resolve.lo select.lo status.lo \
        table.lo tokenize.lo trigger.lo update.lo \
        util.lo vacuum.lo \
        vdbe.lo vdbeapi.lo vdbeaux.lo vdbeblob.lo vdbefifo.lo vdbemem.lo \
        walker.lo where.lo utf.lo vtab.lo

# Object files for the amalgamation.
#
................................................................................
  $(TOP)/src/os_win.c \
  $(TOP)/src/os_os2.c \
  $(TOP)/src/pager.c \
  $(TOP)/src/pager.h \
  $(TOP)/src/parse.y \
  $(TOP)/src/pcache.c \
  $(TOP)/src/pcache.h \

  $(TOP)/src/pragma.c \
  $(TOP)/src/prepare.c \
  $(TOP)/src/printf.c \
  $(TOP)/src/random.c \
  $(TOP)/src/resolve.c \
  $(TOP)/src/select.c \
  $(TOP)/src/status.c \
................................................................................
  $(TOP)/src/malloc.c \
  $(TOP)/src/os.c \
  $(TOP)/src/os_os2.c \
  $(TOP)/src/os_unix.c \
  $(TOP)/src/os_win.c \
  $(TOP)/src/pager.c \
  $(TOP)/src/pcache.c \

  $(TOP)/src/pragma.c \
  $(TOP)/src/prepare.c \
  $(TOP)/src/printf.c \
  $(TOP)/src/random.c \
  $(TOP)/src/select.c \
  $(TOP)/src/tokenize.c \
  $(TOP)/src/utf.c \
................................................................................
	$(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/mutex_w32.c

pager.lo:	$(TOP)/src/pager.c $(HDR) $(TOP)/src/pager.h
	$(LTCOMPILE) -c $(TOP)/src/pager.c

pcache.lo:	$(TOP)/src/pcache.c $(HDR) $(TOP)/src/pcache.h
	$(LTCOMPILE) -c $(TOP)/src/pcache.c




opcodes.lo:	opcodes.c
	$(LTCOMPILE) -c opcodes.c

opcodes.c:	opcodes.h $(TOP)/mkopcodec.awk
	sort -n -b -k 3 opcodes.h | $(NAWK) -f $(TOP)/mkopcodec.awk >opcodes.c








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        btree.lo build.lo callback.lo complete.lo date.lo \
        delete.lo expr.lo fault.lo func.lo global.lo \
        hash.lo journal.lo insert.lo legacy.lo loadext.lo \
        main.lo malloc.lo mem0.lo mem1.lo mem2.lo mem3.lo mem5.lo \
        memjournal.lo \
        mutex.lo mutex_noop.lo mutex_os2.lo mutex_unix.lo mutex_w32.lo \
        opcodes.lo os.lo os_unix.lo os_win.lo os_os2.lo \
        pager.lo parse.lo pcache.lo pcache1.lo pragma.lo prepare.lo printf.lo \
        random.lo resolve.lo select.lo status.lo \
        table.lo tokenize.lo trigger.lo update.lo \
        util.lo vacuum.lo \
        vdbe.lo vdbeapi.lo vdbeaux.lo vdbeblob.lo vdbefifo.lo vdbemem.lo \
        walker.lo where.lo utf.lo vtab.lo

# Object files for the amalgamation.
#
................................................................................
  $(TOP)/src/os_win.c \
  $(TOP)/src/os_os2.c \
  $(TOP)/src/pager.c \
  $(TOP)/src/pager.h \
  $(TOP)/src/parse.y \
  $(TOP)/src/pcache.c \
  $(TOP)/src/pcache.h \
  $(TOP)/src/pcache1.c \
  $(TOP)/src/pragma.c \
  $(TOP)/src/prepare.c \
  $(TOP)/src/printf.c \
  $(TOP)/src/random.c \
  $(TOP)/src/resolve.c \
  $(TOP)/src/select.c \
  $(TOP)/src/status.c \
................................................................................
  $(TOP)/src/malloc.c \
  $(TOP)/src/os.c \
  $(TOP)/src/os_os2.c \
  $(TOP)/src/os_unix.c \
  $(TOP)/src/os_win.c \
  $(TOP)/src/pager.c \
  $(TOP)/src/pcache.c \
  $(TOP)/src/pcache1.c \
  $(TOP)/src/pragma.c \
  $(TOP)/src/prepare.c \
  $(TOP)/src/printf.c \
  $(TOP)/src/random.c \
  $(TOP)/src/select.c \
  $(TOP)/src/tokenize.c \
  $(TOP)/src/utf.c \
................................................................................
	$(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/mutex_w32.c

pager.lo:	$(TOP)/src/pager.c $(HDR) $(TOP)/src/pager.h
	$(LTCOMPILE) -c $(TOP)/src/pager.c

pcache.lo:	$(TOP)/src/pcache.c $(HDR) $(TOP)/src/pcache.h
	$(LTCOMPILE) -c $(TOP)/src/pcache.c

pcache1.lo:	$(TOP)/src/pcache1.c $(HDR) $(TOP)/src/pcache.h
	$(LTCOMPILE) -c $(TOP)/src/pcache1.c

opcodes.lo:	opcodes.c
	$(LTCOMPILE) -c opcodes.c

opcodes.c:	opcodes.h $(TOP)/mkopcodec.awk
	sort -n -b -k 3 opcodes.h | $(NAWK) -f $(TOP)/mkopcodec.awk >opcodes.c

Changes to main.mk.

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         fts3_tokenizer.o fts3_tokenizer1.o \
         func.o global.o hash.o \
         icu.o insert.o journal.o legacy.o loadext.o \
         main.o malloc.o mem0.o mem1.o mem2.o mem3.o mem5.o \
         memjournal.o \
         mutex.o mutex_noop.o mutex_os2.o mutex_unix.o mutex_w32.o \
         opcodes.o os.o os_os2.o os_unix.o os_win.o \
         pager.o parse.o pcache.o pragma.o prepare.o printf.o \
         random.o resolve.o rtree.o select.o status.o \
         table.o tokenize.o trigger.o \
         update.o util.o vacuum.o \
         vdbe.o vdbeapi.o vdbeaux.o vdbeblob.o vdbefifo.o vdbemem.o \
         walker.o where.o utf.o vtab.o


................................................................................
  $(TOP)/src/os_unix.c \
  $(TOP)/src/os_win.c \
  $(TOP)/src/pager.c \
  $(TOP)/src/pager.h \
  $(TOP)/src/parse.y \
  $(TOP)/src/pcache.c \
  $(TOP)/src/pcache.h \

  $(TOP)/src/pragma.c \
  $(TOP)/src/prepare.c \
  $(TOP)/src/printf.c \
  $(TOP)/src/random.c \
  $(TOP)/src/resolve.c \
  $(TOP)/src/select.c \
  $(TOP)/src/status.c \
................................................................................

TESTSRC2 = \
  $(TOP)/src/attach.c $(TOP)/src/btree.c $(TOP)/src/build.c $(TOP)/src/date.c  \
  $(TOP)/src/expr.c $(TOP)/src/func.c $(TOP)/src/insert.c $(TOP)/src/os.c      \
  $(TOP)/src/os_os2.c $(TOP)/src/os_unix.c $(TOP)/src/os_win.c                 \
  $(TOP)/src/pager.c $(TOP)/src/pragma.c $(TOP)/src/prepare.c                  \
  $(TOP)/src/printf.c $(TOP)/src/random.c $(TOP)/src/pcache.c                  \
  $(TOP)/src/select.c $(TOP)/src/tokenize.c                                    \
  $(TOP)/src/utf.c $(TOP)/src/util.c $(TOP)/src/vdbeapi.c $(TOP)/src/vdbeaux.c \
  $(TOP)/src/vdbe.c $(TOP)/src/vdbemem.c $(TOP)/src/where.c parse.c            \
  $(TOP)/ext/fts3/fts3.c $(TOP)/ext/fts3/fts3_tokenizer.c 

# Header files used by all library source files.
#
HDR = \







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         fts3_tokenizer.o fts3_tokenizer1.o \
         func.o global.o hash.o \
         icu.o insert.o journal.o legacy.o loadext.o \
         main.o malloc.o mem0.o mem1.o mem2.o mem3.o mem5.o \
         memjournal.o \
         mutex.o mutex_noop.o mutex_os2.o mutex_unix.o mutex_w32.o \
         opcodes.o os.o os_os2.o os_unix.o os_win.o \
         pager.o parse.o pcache.o pcache1.o pragma.o prepare.o printf.o \
         random.o resolve.o rtree.o select.o status.o \
         table.o tokenize.o trigger.o \
         update.o util.o vacuum.o \
         vdbe.o vdbeapi.o vdbeaux.o vdbeblob.o vdbefifo.o vdbemem.o \
         walker.o where.o utf.o vtab.o


................................................................................
  $(TOP)/src/os_unix.c \
  $(TOP)/src/os_win.c \
  $(TOP)/src/pager.c \
  $(TOP)/src/pager.h \
  $(TOP)/src/parse.y \
  $(TOP)/src/pcache.c \
  $(TOP)/src/pcache.h \
  $(TOP)/src/pcache1.c \
  $(TOP)/src/pragma.c \
  $(TOP)/src/prepare.c \
  $(TOP)/src/printf.c \
  $(TOP)/src/random.c \
  $(TOP)/src/resolve.c \
  $(TOP)/src/select.c \
  $(TOP)/src/status.c \
................................................................................

TESTSRC2 = \
  $(TOP)/src/attach.c $(TOP)/src/btree.c $(TOP)/src/build.c $(TOP)/src/date.c  \
  $(TOP)/src/expr.c $(TOP)/src/func.c $(TOP)/src/insert.c $(TOP)/src/os.c      \
  $(TOP)/src/os_os2.c $(TOP)/src/os_unix.c $(TOP)/src/os_win.c                 \
  $(TOP)/src/pager.c $(TOP)/src/pragma.c $(TOP)/src/prepare.c                  \
  $(TOP)/src/printf.c $(TOP)/src/random.c $(TOP)/src/pcache.c                  \
  $(TOP)/src/pcache1.c $(TOP)/src/select.c $(TOP)/src/tokenize.c               \
  $(TOP)/src/utf.c $(TOP)/src/util.c $(TOP)/src/vdbeapi.c $(TOP)/src/vdbeaux.c \
  $(TOP)/src/vdbe.c $(TOP)/src/vdbemem.c $(TOP)/src/where.c parse.c            \
  $(TOP)/ext/fts3/fts3.c $(TOP)/ext/fts3/fts3_tokenizer.c 

# Header files used by all library source files.
#
HDR = \

Changes to src/btree.c.

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** 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.
**
*************************************************************************
** $Id: btree.c,v 1.534 2008/11/12 18:21:36 danielk1977 Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
#include "btreeInt.h"

................................................................................
** save the state of the cursor.  The cursor must be
** invalidated.
*/
void sqlite3BtreeTripAllCursors(Btree *pBtree, int errCode){
  BtCursor *p;
  sqlite3BtreeEnter(pBtree);
  for(p=pBtree->pBt->pCursor; p; p=p->pNext){

    sqlite3BtreeClearCursor(p);
    p->eState = CURSOR_FAULT;
    p->skip = errCode;




  }
  sqlite3BtreeLeave(pBtree);
}

/*
** Rollback the transaction in progress.  All cursors will be
** invalided by this operation.  Any attempt to use a cursor
................................................................................
  usableSize = pBt->usableSize;
  data = pPage->aData;
  hdr = pPage->hdrOffset;
  cbrk = get2byte(&data[hdr+5]);
  cdata = pChild->aData;
  memcpy(cdata, &data[hdr], pPage->cellOffset+2*pPage->nCell-hdr);
  memcpy(&cdata[cbrk], &data[cbrk], usableSize-cbrk);
  

  rc = sqlite3BtreeInitPage(pChild);
  if( rc==SQLITE_OK ){
    int nCopy = pPage->nOverflow*sizeof(pPage->aOvfl[0]);
    memcpy(pChild->aOvfl, pPage->aOvfl, nCopy);
    pChild->nOverflow = pPage->nOverflow;
    if( pChild->nOverflow ){
      pChild->nFree = 0;







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** 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.
**
*************************************************************************
** $Id: btree.c,v 1.535 2008/11/13 14:28:29 danielk1977 Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
#include "btreeInt.h"

................................................................................
** save the state of the cursor.  The cursor must be
** invalidated.
*/
void sqlite3BtreeTripAllCursors(Btree *pBtree, int errCode){
  BtCursor *p;
  sqlite3BtreeEnter(pBtree);
  for(p=pBtree->pBt->pCursor; p; p=p->pNext){
    int i;
    sqlite3BtreeClearCursor(p);
    p->eState = CURSOR_FAULT;
    p->skip = errCode;
    for(i=0; i<=p->iPage; i++){
      releasePage(p->apPage[i]);
      p->apPage[i] = 0;
    }
  }
  sqlite3BtreeLeave(pBtree);
}

/*
** Rollback the transaction in progress.  All cursors will be
** invalided by this operation.  Any attempt to use a cursor
................................................................................
  usableSize = pBt->usableSize;
  data = pPage->aData;
  hdr = pPage->hdrOffset;
  cbrk = get2byte(&data[hdr+5]);
  cdata = pChild->aData;
  memcpy(cdata, &data[hdr], pPage->cellOffset+2*pPage->nCell-hdr);
  memcpy(&cdata[cbrk], &data[cbrk], usableSize-cbrk);

  assert( pChild->isInit==0 );
  rc = sqlite3BtreeInitPage(pChild);
  if( rc==SQLITE_OK ){
    int nCopy = pPage->nOverflow*sizeof(pPage->aOvfl[0]);
    memcpy(pChild->aOvfl, pPage->aOvfl, nCopy);
    pChild->nOverflow = pPage->nOverflow;
    if( pChild->nOverflow ){
      pChild->nFree = 0;

Changes to src/main.c.

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**
*************************************************************************
** Main file for the SQLite library.  The routines in this file
** implement the programmer interface to the library.  Routines in
** other files are for internal use by SQLite and should not be
** accessed by users of the library.
**
** $Id: main.c,v 1.511 2008/11/10 18:05:36 shane Exp $
*/
#include "sqliteInt.h"
#include <ctype.h>

#ifdef SQLITE_ENABLE_FTS3
# include "fts3.h"
#endif
................................................................................
    case SQLITE_CONFIG_PAGECACHE: {
      /* Designate a buffer for scratch memory space */
      sqlite3GlobalConfig.pPage = va_arg(ap, void*);
      sqlite3GlobalConfig.szPage = va_arg(ap, int);
      sqlite3GlobalConfig.nPage = va_arg(ap, int);
      break;
    }







#if defined(SQLITE_ENABLE_MEMSYS3) || defined(SQLITE_ENABLE_MEMSYS5)
    case SQLITE_CONFIG_HEAP: {
      /* Designate a buffer for heap memory space */
      sqlite3GlobalConfig.pHeap = va_arg(ap, void*);
      sqlite3GlobalConfig.nHeap = va_arg(ap, int);
      sqlite3GlobalConfig.mnReq = va_arg(ap, int);







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**
*************************************************************************
** Main file for the SQLite library.  The routines in this file
** implement the programmer interface to the library.  Routines in
** other files are for internal use by SQLite and should not be
** accessed by users of the library.
**
** $Id: main.c,v 1.512 2008/11/13 14:28:29 danielk1977 Exp $
*/
#include "sqliteInt.h"
#include <ctype.h>

#ifdef SQLITE_ENABLE_FTS3
# include "fts3.h"
#endif
................................................................................
    case SQLITE_CONFIG_PAGECACHE: {
      /* Designate a buffer for scratch memory space */
      sqlite3GlobalConfig.pPage = va_arg(ap, void*);
      sqlite3GlobalConfig.szPage = va_arg(ap, int);
      sqlite3GlobalConfig.nPage = va_arg(ap, int);
      break;
    }

    case SQLITE_CONFIG_PCACHE: {
      /* Specify an alternative malloc implementation */
      sqlite3GlobalConfig.pcache = *va_arg(ap, sqlite3_pcache_methods*);
      break;
    }

#if defined(SQLITE_ENABLE_MEMSYS3) || defined(SQLITE_ENABLE_MEMSYS5)
    case SQLITE_CONFIG_HEAP: {
      /* Designate a buffer for heap memory space */
      sqlite3GlobalConfig.pHeap = va_arg(ap, void*);
      sqlite3GlobalConfig.nHeap = va_arg(ap, int);
      sqlite3GlobalConfig.mnReq = va_arg(ap, int);

Changes to src/pager.c.

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** The pager is used to access a database disk file.  It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file.  The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.502 2008/11/07 00:24:54 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"

/*
** Macros for troubleshooting.  Normally turned off
*/
................................................................................
** journal (or statement snapshot has been created, if *pPg is part
** of an in-memory database).
*/
static int pageInStatement(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  return sqlite3BitvecTest(pPager->pInStmt, pPg->pgno);
}





/*
** Read a 32-bit integer from the given file descriptor.  Store the integer
** that is read in *pRes.  Return SQLITE_OK if everything worked, or an
** error code is something goes wrong.
**
** All values are stored on disk as big-endian.
................................................................................
    hash = (hash*1039) + pData[i];
  }
  return hash;
}
static u32 pager_pagehash(PgHdr *pPage){
  return pager_datahash(pPage->pPager->pageSize, (unsigned char *)pPage->pData);
}
static u32 pager_set_pagehash(PgHdr *pPage){
  pPage->pageHash = pager_pagehash(pPage);
}

/*
** The CHECK_PAGE macro takes a PgHdr* as an argument. If SQLITE_CHECK_PAGES
** is defined, and NDEBUG is not defined, an assert() statement checks
** that the page is either dirty or still matches the calculated page-hash.
................................................................................
        rc = sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
      }
    }
    sqlite3BitvecDestroy(pPager->pInJournal);
    pPager->pInJournal = 0;
    sqlite3BitvecDestroy(pPager->pAlwaysRollback);
    pPager->pAlwaysRollback = 0;
    sqlite3PcacheCleanAll(pPager->pPCache);
#ifdef SQLITE_CHECK_PAGES
    sqlite3PcacheIterate(pPager->pPCache, pager_set_pagehash);
#endif
    sqlite3PcacheClearFlags(pPager->pPCache,
       PGHDR_IN_JOURNAL | PGHDR_NEED_SYNC
    );
    pPager->dirtyCache = 0;
    pPager->nRec = 0;
  }else{
    assert( pPager->pInJournal==0 );
  }

  if( !pPager->exclusiveMode ){
................................................................................
      }
      pPager->journalStarted = 1;
    }
    pPager->needSync = 0;

    /* Erase the needSync flag from every page.
    */
    sqlite3PcacheClearFlags(pPager->pPCache, PGHDR_NEED_SYNC);
  }

#ifndef NDEBUG
  /* If the Pager.needSync flag is clear then the PgHdr.needSync
  ** flag must also be clear for all pages.  Verify that this
  ** invariant is true.
  */
  else{
    sqlite3PcacheAssertFlags(pPager->pPCache, 0, PGHDR_NEED_SYNC);
  }
#endif

  return rc;
}

/*
** Given a list of pages (connected by the PgHdr.pDirty pointer) write
** every one of those pages out to the database file. No calls are made
** to the page-cache to mark the pages as clean. It is the responsibility
................................................................................
  if( pPg->pPager==0 ){
    /* The pager cache has created a new page. Its content needs to 
    ** be initialized.
    */
    int nMax;
    PAGER_INCR(pPager->nMiss);
    pPg->pPager = pPager;
    if( sqlite3BitvecTest(pPager->pInJournal, pgno) ){
      pPg->flags |= PGHDR_IN_JOURNAL;
    }
    memset(pPg->pExtra, 0, pPager->nExtra);

    rc = sqlite3PagerPagecount(pPager, &nMax);
    if( rc!=SQLITE_OK ){
      sqlite3PagerUnref(pPg);
      return rc;
    }
................................................................................
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;
  assert( pPg->nRef>0 );
  assert( pPager->state!=PAGER_UNLOCK );
  if( pPager->state==PAGER_SHARED ){
    assert( pPager->pInJournal==0 );
    assert( !MEMDB );
    sqlite3PcacheAssertFlags(pPager->pPCache, 0, PGHDR_IN_JOURNAL);
    rc = sqlite3OsLock(pPager->fd, RESERVED_LOCK);
    if( rc==SQLITE_OK ){
      pPager->state = PAGER_RESERVED;
      if( exFlag ){
        rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
      }
    }
................................................................................
    return rc;
  }

  /* Mark the page as dirty.  If the page has already been written
  ** to the journal then we can return right away.
  */
  makeDirty(pPg);
  if( (pPg->flags&PGHDR_IN_JOURNAL)
   && (pageInStatement(pPg) || pPager->stmtInUse==0) 
  ){
    pPager->dirtyCache = 1;
    pPager->dbModified = 1;
  }else{

    /* If we get this far, it means that the page needs to be
    ** written to the transaction journal or the ckeckpoint journal
    ** or both.
................................................................................
    pPager->dirtyCache = 1;
    pPager->dbModified = 1;
  
    /* The transaction journal now exists and we have a RESERVED or an
    ** EXCLUSIVE lock on the main database file.  Write the current page to
    ** the transaction journal if it is not there already.
    */
    if( !(pPg->flags&PGHDR_IN_JOURNAL) && pPager->journalOpen ){
      if( (int)pPg->pgno <= pPager->origDbSize ){
        u32 cksum;
        char *pData2;

        /* We should never write to the journal file the page that
        ** contains the database locks.  The following assert verifies
        ** that we do not. */
................................................................................
        PAGERTRACE4("APPEND %d page %d needSync=%d\n",
                PAGERID(pPager), pPg->pgno,
               ((pPg->flags&PGHDR_NEED_SYNC)?1:0));
      }
      if( pPg->flags&PGHDR_NEED_SYNC ){
        pPager->needSync = 1;
      }
      pPg->flags |= PGHDR_IN_JOURNAL;
    }
  
    /* If the statement journal is open and the page is not in it,
    ** then write the current page to the statement journal.  Note that
    ** the statement journal format differs from the standard journal format
    ** in that it omits the checksums and the header.
    */
    if( pPager->stmtInUse 
     && !pageInStatement(pPg) 
     && (int)pPg->pgno<=pPager->stmtSize 
    ){
      i64 offset = pPager->stmtNRec*(4+pPager->pageSize);
      char *pData2 = CODEC2(pPager, pData, pPg->pgno, 7);
      assert( (pPg->flags&PGHDR_IN_JOURNAL) 
                 || (int)pPg->pgno>pPager->origDbSize );
      rc = write32bits(pPager->stfd, offset, pPg->pgno);
      if( rc==SQLITE_OK ){
        rc = sqlite3OsWrite(pPager->stfd, pData2, pPager->pageSize, offset+4);
      }
      PAGERTRACE3("STMT-JOURNAL %d page %d\n", PAGERID(pPager), pPg->pgno);
      if( rc!=SQLITE_OK ){
        return rc;
................................................................................
  ** pages on the freelist (ex: corrupt9.test) then the following is not
  ** necessarily true:
  */
  /* assert( !pPg->inJournal && (int)pPg->pgno <= pPager->origDbSize ); */

  assert( pPager->pInJournal!=0 );
  sqlite3BitvecSet(pPager->pInJournal, pPg->pgno);
  pPg->flags |= PGHDR_IN_JOURNAL;
  pPg->flags &= ~PGHDR_NEED_READ;
  if( pPager->stmtInUse ){
    assert( pPager->stmtSize >= pPager->origDbSize );
    sqlite3BitvecSet(pPager->pInStmt, pPg->pgno);
  }
  PAGERTRACE3("DONT_ROLLBACK page %d of %d\n", pPg->pgno, PAGERID(pPager));
  IOTRACE(("GARBAGE %p %d\n", pPager, pPg->pgno))
................................................................................
  **
  ** If the isCommit flag is set, there is no need to remember that
  ** the journal needs to be sync()ed before database page pPg->pgno 
  ** can be written to. The caller has already promised not to write to it.
  */
  if( (pPg->flags&PGHDR_NEED_SYNC) && !isCommit ){
    needSyncPgno = pPg->pgno;
    assert( (pPg->flags&PGHDR_IN_JOURNAL) || (int)pgno>pPager->origDbSize );
    assert( pPg->flags&PGHDR_DIRTY );
    assert( pPager->needSync );
  }

  /* If the cache contains a page with page-number pgno, remove it
  ** from its hash chain. Also, if the PgHdr.needSync was set for 
  ** page pgno before the 'move' operation, it needs to be retained 
  ** for the page moved there.
  */
  pPg->flags &= ~(PGHDR_NEED_SYNC|PGHDR_IN_JOURNAL);
  pPgOld = pager_lookup(pPager, pgno);
  assert( !pPgOld || pPgOld->nRef==1 );
  if( pPgOld ){
    pPg->flags |= (pPgOld->flags&PGHDR_NEED_SYNC);
  }
  if( sqlite3BitvecTest(pPager->pInJournal, pgno) ){
    pPg->flags |= PGHDR_IN_JOURNAL;
  }

  sqlite3PcacheMove(pPg, pgno);
  if( pPgOld ){
    sqlite3PcacheMove(pPgOld, 0);
    sqlite3PcacheRelease(pPgOld);
  }

  makeDirty(pPg);
  pPager->dirtyCache = 1;
  pPager->dbModified = 1;

  if( needSyncPgno ){
................................................................................
        sqlite3BitvecClear(pPager->pInJournal, needSyncPgno);
      }
      return rc;
    }
    pPager->needSync = 1;
    assert( pPager->noSync==0 && !MEMDB );
    pPgHdr->flags |= PGHDR_NEED_SYNC;
    pPgHdr->flags |= PGHDR_IN_JOURNAL;
    makeDirty(pPgHdr);
    sqlite3PagerUnref(pPgHdr);
  }

  return SQLITE_OK;
}
#endif







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** The pager is used to access a database disk file.  It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file.  The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.503 2008/11/13 14:28:29 danielk1977 Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"

/*
** Macros for troubleshooting.  Normally turned off
*/
................................................................................
** journal (or statement snapshot has been created, if *pPg is part
** of an in-memory database).
*/
static int pageInStatement(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  return sqlite3BitvecTest(pPager->pInStmt, pPg->pgno);
}

static int pageInJournal(PgHdr *pPg){
  return sqlite3BitvecTest(pPg->pPager->pInJournal, pPg->pgno);
}

/*
** Read a 32-bit integer from the given file descriptor.  Store the integer
** that is read in *pRes.  Return SQLITE_OK if everything worked, or an
** error code is something goes wrong.
**
** All values are stored on disk as big-endian.
................................................................................
    hash = (hash*1039) + pData[i];
  }
  return hash;
}
static u32 pager_pagehash(PgHdr *pPage){
  return pager_datahash(pPage->pPager->pageSize, (unsigned char *)pPage->pData);
}
static void pager_set_pagehash(PgHdr *pPage){
  pPage->pageHash = pager_pagehash(pPage);
}

/*
** The CHECK_PAGE macro takes a PgHdr* as an argument. If SQLITE_CHECK_PAGES
** is defined, and NDEBUG is not defined, an assert() statement checks
** that the page is either dirty or still matches the calculated page-hash.
................................................................................
        rc = sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
      }
    }
    sqlite3BitvecDestroy(pPager->pInJournal);
    pPager->pInJournal = 0;
    sqlite3BitvecDestroy(pPager->pAlwaysRollback);
    pPager->pAlwaysRollback = 0;

#ifdef SQLITE_CHECK_PAGES
    sqlite3PcacheIterateDirty(pPager->pPCache, pager_set_pagehash);
#endif
    sqlite3PcacheCleanAll(pPager->pPCache);


    pPager->dirtyCache = 0;
    pPager->nRec = 0;
  }else{
    assert( pPager->pInJournal==0 );
  }

  if( !pPager->exclusiveMode ){
................................................................................
      }
      pPager->journalStarted = 1;
    }
    pPager->needSync = 0;

    /* Erase the needSync flag from every page.
    */
    sqlite3PcacheClearSyncFlags(pPager->pPCache);
  }











  return rc;
}

/*
** Given a list of pages (connected by the PgHdr.pDirty pointer) write
** every one of those pages out to the database file. No calls are made
** to the page-cache to mark the pages as clean. It is the responsibility
................................................................................
  if( pPg->pPager==0 ){
    /* The pager cache has created a new page. Its content needs to 
    ** be initialized.
    */
    int nMax;
    PAGER_INCR(pPager->nMiss);
    pPg->pPager = pPager;



    memset(pPg->pExtra, 0, pPager->nExtra);

    rc = sqlite3PagerPagecount(pPager, &nMax);
    if( rc!=SQLITE_OK ){
      sqlite3PagerUnref(pPg);
      return rc;
    }
................................................................................
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;
  assert( pPg->nRef>0 );
  assert( pPager->state!=PAGER_UNLOCK );
  if( pPager->state==PAGER_SHARED ){
    assert( pPager->pInJournal==0 );
    assert( !MEMDB );

    rc = sqlite3OsLock(pPager->fd, RESERVED_LOCK);
    if( rc==SQLITE_OK ){
      pPager->state = PAGER_RESERVED;
      if( exFlag ){
        rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
      }
    }
................................................................................
    return rc;
  }

  /* Mark the page as dirty.  If the page has already been written
  ** to the journal then we can return right away.
  */
  makeDirty(pPg);

  if( pageInJournal(pPg) && (pageInStatement(pPg) || pPager->stmtInUse==0) ){

    pPager->dirtyCache = 1;
    pPager->dbModified = 1;
  }else{

    /* If we get this far, it means that the page needs to be
    ** written to the transaction journal or the ckeckpoint journal
    ** or both.
................................................................................
    pPager->dirtyCache = 1;
    pPager->dbModified = 1;
  
    /* The transaction journal now exists and we have a RESERVED or an
    ** EXCLUSIVE lock on the main database file.  Write the current page to
    ** the transaction journal if it is not there already.
    */
    if( !pageInJournal(pPg) && pPager->journalOpen ){
      if( (int)pPg->pgno <= pPager->origDbSize ){
        u32 cksum;
        char *pData2;

        /* We should never write to the journal file the page that
        ** contains the database locks.  The following assert verifies
        ** that we do not. */
................................................................................
        PAGERTRACE4("APPEND %d page %d needSync=%d\n",
                PAGERID(pPager), pPg->pgno,
               ((pPg->flags&PGHDR_NEED_SYNC)?1:0));
      }
      if( pPg->flags&PGHDR_NEED_SYNC ){
        pPager->needSync = 1;
      }

    }
  
    /* If the statement journal is open and the page is not in it,
    ** then write the current page to the statement journal.  Note that
    ** the statement journal format differs from the standard journal format
    ** in that it omits the checksums and the header.
    */
    if( pPager->stmtInUse 
     && !pageInStatement(pPg) 
     && (int)pPg->pgno<=pPager->stmtSize 
    ){
      i64 offset = pPager->stmtNRec*(4+pPager->pageSize);
      char *pData2 = CODEC2(pPager, pData, pPg->pgno, 7);

      assert( pageInJournal(pPg) || (int)pPg->pgno>pPager->origDbSize );
      rc = write32bits(pPager->stfd, offset, pPg->pgno);
      if( rc==SQLITE_OK ){
        rc = sqlite3OsWrite(pPager->stfd, pData2, pPager->pageSize, offset+4);
      }
      PAGERTRACE3("STMT-JOURNAL %d page %d\n", PAGERID(pPager), pPg->pgno);
      if( rc!=SQLITE_OK ){
        return rc;
................................................................................
  ** pages on the freelist (ex: corrupt9.test) then the following is not
  ** necessarily true:
  */
  /* assert( !pPg->inJournal && (int)pPg->pgno <= pPager->origDbSize ); */

  assert( pPager->pInJournal!=0 );
  sqlite3BitvecSet(pPager->pInJournal, pPg->pgno);

  pPg->flags &= ~PGHDR_NEED_READ;
  if( pPager->stmtInUse ){
    assert( pPager->stmtSize >= pPager->origDbSize );
    sqlite3BitvecSet(pPager->pInStmt, pPg->pgno);
  }
  PAGERTRACE3("DONT_ROLLBACK page %d of %d\n", pPg->pgno, PAGERID(pPager));
  IOTRACE(("GARBAGE %p %d\n", pPager, pPg->pgno))
................................................................................
  **
  ** If the isCommit flag is set, there is no need to remember that
  ** the journal needs to be sync()ed before database page pPg->pgno 
  ** can be written to. The caller has already promised not to write to it.
  */
  if( (pPg->flags&PGHDR_NEED_SYNC) && !isCommit ){
    needSyncPgno = pPg->pgno;
    assert( pageInJournal(pPg) || (int)pgno>pPager->origDbSize );
    assert( pPg->flags&PGHDR_DIRTY );
    assert( pPager->needSync );
  }

  /* If the cache contains a page with page-number pgno, remove it
  ** from its hash chain. Also, if the PgHdr.needSync was set for 
  ** page pgno before the 'move' operation, it needs to be retained 
  ** for the page moved there.
  */
  pPg->flags &= ~PGHDR_NEED_SYNC;
  pPgOld = pager_lookup(pPager, pgno);
  assert( !pPgOld || pPgOld->nRef==1 );
  if( pPgOld ){
    pPg->flags |= (pPgOld->flags&PGHDR_NEED_SYNC);
  }




  sqlite3PcacheMove(pPg, pgno);
  if( pPgOld ){
    sqlite3PcacheDrop(pPgOld);

  }

  makeDirty(pPg);
  pPager->dirtyCache = 1;
  pPager->dbModified = 1;

  if( needSyncPgno ){
................................................................................
        sqlite3BitvecClear(pPager->pInJournal, needSyncPgno);
      }
      return rc;
    }
    pPager->needSync = 1;
    assert( pPager->noSync==0 && !MEMDB );
    pPgHdr->flags |= PGHDR_NEED_SYNC;

    makeDirty(pPgHdr);
    sqlite3PagerUnref(pPgHdr);
  }

  return SQLITE_OK;
}
#endif

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**    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.
**
** @(#) $Id: pcache.c,v 1.36 2008/11/11 18:43:00 danielk1977 Exp $
*/
#include "sqliteInt.h"

/*
** A complete page cache is an instance of this structure.
**
** A cache may only be deleted by its owner and while holding the
** SQLITE_MUTEX_STATUS_LRU mutex.
*/
struct PCache {
  /*********************************************************************
  ** The first group of elements may be read or written at any time by
  ** the cache owner without holding the mutex.  No thread other than the
  ** cache owner is permitted to access these elements at any time.
  */
  PgHdr *pDirty, *pDirtyTail;         /* List of dirty pages in LRU order */
  PgHdr *pSynced;                     /* Last synced page in dirty page list */
  int nRef;                           /* Number of pinned pages */
  int nPinned;                        /* Number of pinned and/or dirty pages */
  int nMax;                           /* Configured cache size */
  int nMin;                           /* Configured minimum cache size */
  /**********************************************************************
  ** The next group of elements are fixed when the cache is created and
  ** may not be changed afterwards.  These elements can read at any time by
  ** the cache owner or by any thread holding the the mutex.  Non-owner
  ** threads must hold the mutex when reading these elements to prevent
  ** the entire PCache object from being deleted during the read.
  */
  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 */
  /**********************************************************************
  ** The final group of elements can only be accessed while holding the
  ** mutex.  Both the cache owner and any other thread must hold the mutex
  ** to read or write any of these elements.
  */
  int nPage;                          /* Total number of pages in apHash */
  int nHash;                          /* Number of slots in apHash[] */
  PgHdr **apHash;                     /* Hash table for fast lookup by pgno */
  PgHdr *pClean;                      /* List of clean pages in use */
};

/*
** Free slots in the page block allocator
*/
typedef struct PgFreeslot PgFreeslot;
struct PgFreeslot {
  PgFreeslot *pNext;  /* Next free slot */
};

/*
** Global data for the page cache.
*/
static SQLITE_WSD struct PCacheGlobal {
  int isInit;                         /* True when initialized */
  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 */
  PgHdr *pLruHead, *pLruTail;         /* LRU list of unused clean pgs */

  /* 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 */
} pcache = {0};

/*
** All code in this file should access the global pcache structure via the
** alias "pcache_g". This ensures that the WSD emulation is used when
** compiling for systems that do not support real WSD.
*/
#define pcache_g (GLOBAL(struct PCacheGlobal, pcache))

/*
** All global variables used by this module (all of which are grouped 
** together in global structure "pcache" above) are protected by the static 
** SQLITE_MUTEX_STATIC_LRU mutex. A pointer to this mutex is stored in
** variable "pcache.mutex".
**
** Some elements of the PCache and PgHdr structures are protected by the 
** SQLITE_MUTEX_STATUS_LRU mutex and other are not.  The protected
** elements are grouped at the end of the structures and are clearly
** marked.
**
** Use the following macros must surround all access (read or write)
** of protected elements.  The mutex is not recursive and may not be
** entered more than once.  The pcacheMutexHeld() macro should only be
** used within an assert() to verify that the mutex is being held.
*/
#define pcacheEnterMutex() sqlite3_mutex_enter(pcache_g.mutex)
#define pcacheExitMutex()  sqlite3_mutex_leave(pcache_g.mutex)
#define pcacheMutexHeld()  sqlite3_mutex_held(pcache_g.mutex)

/*
** 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)
/*
** This routine verifies that the number of entries in the hash table
** is pCache->nPage.  This routine is used within assert() statements
** only and is therefore disabled during production builds.
*/
static int pcacheCheckHashCount(PCache *pCache){
  int i;
  int nPage = 0;
  for(i=0; i<pCache->nHash; i++){
    PgHdr *p;
    for(p=pCache->apHash[i]; p; p=p->pNextHash){
      nPage++;
    }
  }
  assert( nPage==pCache->nPage );
  return 1;
}
#endif /* !NDEBUG && SQLITE_ENABLE_EXPENSIVE_ASSERT */


#if !defined(NDEBUG) && defined(SQLITE_ENABLE_EXPENSIVE_ASSERT)
/*
** Based on the current value of PCache.nRef and the contents of the
** PCache.pDirty list, return the expected value of the PCache.nPinned
** counter. This is only used in debugging builds, as follows:
**
**   expensive_assert( pCache->nPinned==pcachePinnedCount(pCache) );
*/
static int pcachePinnedCount(PCache *pCache){
  PgHdr *p;
  int nPinned = pCache->nRef;
  for(p=pCache->pDirty; p; p=p->pNext){
    if( p->nRef==0 ){
      nPinned++;
    }
  }
  return nPinned;
}
#endif /* !NDEBUG && SQLITE_ENABLE_EXPENSIVE_ASSERT */


#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 = pCache->pDirtyTail;
  for(p=pCache->pDirtyTail; p!=pCache->pSynced; p=p->pPrev){
    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 a page from its hash table (PCache.apHash[]).

*/
static void pcacheRemoveFromHash(PgHdr *pPage){
  assert( pcacheMutexHeld() );
  if( pPage->pPrevHash ){
    pPage->pPrevHash->pNextHash = pPage->pNextHash;
  }else{
    PCache *pCache = pPage->pCache;
    u32 h = pPage->pgno % pCache->nHash;
    assert( pCache->apHash[h]==pPage );
    pCache->apHash[h] = pPage->pNextHash;
  }
  if( pPage->pNextHash ){
    pPage->pNextHash->pPrevHash = pPage->pPrevHash;


  }
  pPage->pCache->nPage--;
  expensive_assert( pcacheCheckHashCount(pPage->pCache) );
}

/*
** Insert a page into the hash table
**
** The mutex must be held by the caller.
*/
static void pcacheAddToHash(PgHdr *pPage){
  PCache *pCache = pPage->pCache;
  u32 h = pPage->pgno % pCache->nHash;
  assert( pcacheMutexHeld() );
  pPage->pNextHash = pCache->apHash[h];
  pPage->pPrevHash = 0;
  if( pCache->apHash[h] ){
    pCache->apHash[h]->pPrevHash = pPage;
  }
  pCache->apHash[h] = pPage;
  pCache->nPage++;
  expensive_assert( pcacheCheckHashCount(pCache) );
}

/*
** Attempt to increase the size the hash table to contain
** at least nHash buckets.
*/
static int pcacheResizeHash(PCache *pCache, int nHash){
  PgHdr *p;
  PgHdr **pNew;
  assert( pcacheMutexHeld() );
#ifdef SQLITE_MALLOC_SOFT_LIMIT
  if( nHash*sizeof(PgHdr*)>SQLITE_MALLOC_SOFT_LIMIT ){
    nHash = SQLITE_MALLOC_SOFT_LIMIT/sizeof(PgHdr *);
  }
#endif
  pcacheExitMutex();
  pNew = (PgHdr **)sqlite3Malloc(sizeof(PgHdr*)*nHash);
  pcacheEnterMutex();
  if( !pNew ){
    return SQLITE_NOMEM;
  }
  memset(pNew, 0, sizeof(PgHdr *)*nHash);
  sqlite3_free(pCache->apHash);
  pCache->apHash = pNew;
  pCache->nHash = nHash;
  pCache->nPage = 0;
 
  for(p=pCache->pClean; p; p=p->pNext){
    pcacheAddToHash(p);
  }
  for(p=pCache->pDirty; p; p=p->pNext){
    pcacheAddToHash(p);
  }
  return SQLITE_OK;
}

/*
** Remove a page from a linked list that is headed by *ppHead.
** *ppHead is either PCache.pClean or PCache.pDirty.
*/
static void pcacheRemoveFromList(PgHdr **ppHead, PgHdr *pPage){
  int isDirtyList = (ppHead==&pPage->pCache->pDirty);
  assert( ppHead==&pPage->pCache->pClean || ppHead==&pPage->pCache->pDirty );
  assert( pcacheMutexHeld() || ppHead!=&pPage->pCache->pClean );

  if( pPage->pPrev ){
    pPage->pPrev->pNext = pPage->pNext;
  }else{
    assert( *ppHead==pPage );
    *ppHead = pPage->pNext;
  }
  if( pPage->pNext ){
    pPage->pNext->pPrev = pPage->pPrev;
  }

  if( isDirtyList ){
    PCache *pCache = pPage->pCache;
    assert( pPage->pNext || pCache->pDirtyTail==pPage );
    if( !pPage->pNext ){
      pCache->pDirtyTail = pPage->pPrev;
    }

    if( pCache->pSynced==pPage ){
      PgHdr *pSynced = pPage->pPrev;
      while( pSynced && (pSynced->flags&PGHDR_NEED_SYNC) ){
        pSynced = pSynced->pPrev;
      }
      pCache->pSynced = pSynced;
    }
  }
}

/*
** Add a page from a linked list that is headed by *ppHead.
** *ppHead is either PCache.pClean or PCache.pDirty.
*/
static void pcacheAddToList(PgHdr **ppHead, PgHdr *pPage){
  int isDirtyList = (ppHead==&pPage->pCache->pDirty);
  assert( ppHead==&pPage->pCache->pClean || ppHead==&pPage->pCache->pDirty );

  if( (*ppHead) ){
    (*ppHead)->pPrev = pPage;
  }
  pPage->pNext = *ppHead;
  pPage->pPrev = 0;
  *ppHead = pPage;

  if( isDirtyList ){
    PCache *pCache = pPage->pCache;


    if( !pCache->pDirtyTail ){
      assert( pPage->pNext==0 );
      pCache->pDirtyTail = pPage;
    }
    if( !pCache->pSynced && 0==(pPage->flags&PGHDR_NEED_SYNC) ){
      pCache->pSynced = pPage;
    }
  }
}

/*
** Remove a page from the global LRU list
*/
static void pcacheRemoveFromLruList(PgHdr *pPage){
  assert( sqlite3_mutex_held(pcache_g.mutex) );
  assert( (pPage->flags&PGHDR_DIRTY)==0 );
  if( pPage->pCache->bPurgeable==0 ) return;
  if( pPage->pNextLru ){
    assert( pcache_g.pLruTail!=pPage );
    pPage->pNextLru->pPrevLru = pPage->pPrevLru;

  }else{
    assert( pcache_g.pLruTail==pPage );
    pcache_g.pLruTail = pPage->pPrevLru;


  }
  if( pPage->pPrevLru ){
    assert( pcache_g.pLruHead!=pPage );
    pPage->pPrevLru->pNextLru = pPage->pNextLru;
  }else{
    assert( pcache_g.pLruHead==pPage );
    pcache_g.pLruHead = pPage->pNextLru;

  }

}

/*
** Add a page to the global LRU list.  The page is normally added
** to the front of the list so that it will be the last page recycled.
** However, if the PGHDR_REUSE_UNLIKELY bit is set, the page is added
** to the end of the LRU list so that it will be the next to be recycled.


*/
static void pcacheAddToLruList(PgHdr *pPage){
  assert( sqlite3_mutex_held(pcache_g.mutex) );
  assert( (pPage->flags&PGHDR_DIRTY)==0 );
  if( pPage->pCache->bPurgeable==0 ) return;
  if( pcache_g.pLruTail && (pPage->flags & PGHDR_REUSE_UNLIKELY)!=0 ){
    /* If reuse is unlikely.  Put the page at the end of the LRU list
    ** where it will be recycled sooner rather than later. 
    */
    assert( pcache_g.pLruHead );
    pPage->pNextLru = 0;
    pPage->pPrevLru = pcache_g.pLruTail;
    pcache_g.pLruTail->pNextLru = pPage;
    pcache_g.pLruTail = pPage;
    pPage->flags &= ~PGHDR_REUSE_UNLIKELY;
  }else{
    /* If reuse is possible. the page goes at the beginning of the LRU
    ** list so that it will be the last to be recycled.
    */
    if( pcache_g.pLruHead ){
      pcache_g.pLruHead->pPrevLru = pPage;
    }
    pPage->pNextLru = pcache_g.pLruHead;
    pcache_g.pLruHead = pPage;
    pPage->pPrevLru = 0;
    if( pcache_g.pLruTail==0 ){
      pcache_g.pLruTail = pPage;

    }




  }



}



/*********************************************** Memory Allocation ***********
**
** Initialize the page cache memory pool.
**
** This must be called at start-time when no page cache lines are
** checked out. This function is not threadsafe.
*/
void sqlite3PCacheBufferSetup(void *pBuf, int sz, int n){
  PgFreeslot *p;
  sz &= ~7;
  pcache_g.szSlot = sz;
  pcache_g.pStart = pBuf;
  pcache_g.pFree = 0;
  while( n-- ){
    p = (PgFreeslot*)pBuf;
    p->pNext = pcache_g.pFree;
    pcache_g.pFree = p;
    pBuf = (void*)&((char*)pBuf)[sz];

  }
  pcache_g.pEnd = pBuf;
}

/*
** Allocate a page cache line.  Look in the page cache memory pool first
** and use an element from it first if available.  If nothing is available
** in the page cache memory pool, go to the general purpose memory allocator.


*/
static void *pcacheMalloc(int sz, PCache *pCache){
  assert( sqlite3_mutex_held(pcache_g.mutex) );
  if( sz<=pcache_g.szSlot && pcache_g.pFree ){
    PgFreeslot *p = pcache_g.pFree;
    pcache_g.pFree = p->pNext;
    sqlite3StatusSet(SQLITE_STATUS_PAGECACHE_SIZE, sz);
    sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_USED, 1);
    return (void*)p;
  }else{
    void *p;

    /* 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.
    */
    pcacheExitMutex();
    p = sqlite3Malloc(sz);
    pcacheEnterMutex();

    if( p ){
      sz = sqlite3MallocSize(p);
      sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_OVERFLOW, sz);
    }
    return p;
  }
}
void *sqlite3PageMalloc(int sz){
  void *p;
  pcacheEnterMutex();
  p = pcacheMalloc(sz, 0);
  pcacheExitMutex();
  return p;
}

/*
** Release a pager memory allocation
*/
static void pcacheFree(void *p){
  assert( sqlite3_mutex_held(pcache_g.mutex) );
  if( p==0 ) return;
  if( p>=pcache_g.pStart && p<pcache_g.pEnd ){
    PgFreeslot *pSlot;
    sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_USED, -1);
    pSlot = (PgFreeslot*)p;
    pSlot->pNext = pcache_g.pFree;
    pcache_g.pFree = pSlot;
  }else{
    int iSize = sqlite3MallocSize(p);
    sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_OVERFLOW, -iSize);
    sqlite3_free(p);
  }
}
void sqlite3PageFree(void *p){
  pcacheEnterMutex();
  pcacheFree(p);
  pcacheExitMutex();
}

/*
** Allocate a new page.
*/
static PgHdr *pcachePageAlloc(PCache *pCache){
  PgHdr *p;
  int sz = sizeof(*p) + pCache->szPage + pCache->szExtra;
  assert( sqlite3_mutex_held(pcache_g.mutex) );
  p = pcacheMalloc(sz, pCache);
  if( p==0 ) return 0;
  memset(p, 0, sizeof(PgHdr));
  p->pData = (void*)&p[1];
  p->pExtra = (void*)&((char*)p->pData)[pCache->szPage];
  if( pCache->bPurgeable ){
    pcache_g.nCurrentPage++;
  }
  return p;
}

/*
** Deallocate a page
*/
static void pcachePageFree(PgHdr *p){
  assert( sqlite3_mutex_held(pcache_g.mutex) );
  if( p->pCache->bPurgeable ){
    pcache_g.nCurrentPage--;
  }
  pcacheFree(p);
}

#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
/*
** Return the number of bytes that will be returned to the heap when
** the argument is passed to pcachePageFree().
*/
static int pcachePageSize(PgHdr *p){
  assert( sqlite3_mutex_held(pcache_g.mutex) );
  assert( !pcache_g.pStart );
  assert( p && p->pCache );
  return sqlite3MallocSize(p);
}
#endif

/*
** Attempt to 'recycle' a page from the global LRU list. Only clean,
** unreferenced pages from purgeable caches are eligible for recycling.
**
** This function removes page pcache.pLruTail from the global LRU list,
** and from the hash-table and PCache.pClean list of the owner pcache.
** There should be no other references to the page.
**
** A pointer to the recycled page is returned, or NULL if no page is
** eligible for recycling.
*/
static PgHdr *pcacheRecyclePage(void){
  PgHdr *p = 0;
  assert( sqlite3_mutex_held(pcache_g.mutex) );

  if( (p=pcache_g.pLruTail)!=0 ){
    assert( (p->flags&PGHDR_DIRTY)==0 );
    pcacheRemoveFromLruList(p);
    pcacheRemoveFromHash(p);
    pcacheRemoveFromList(&p->pCache->pClean, p);
  }

  return p;
}

/*
** Obtain space for a page. Try to recycle an old page if the limit on the 
** number of pages has been reached. If the limit has not been reached or
** there are no pages eligible for recycling, allocate a new page.
**
** Return a pointer to the new page, or NULL if an OOM condition occurs.
*/
static int pcacheRecycleOrAlloc(PCache *pCache, PgHdr **ppPage){
  PgHdr *p = 0;

  int szPage = pCache->szPage;
  int szExtra = pCache->szExtra;

  assert( pcache_g.isInit );
  assert( sqlite3_mutex_held(pcache_g.mutex) );

  *ppPage = 0;

  /* If we have reached either the global or the local limit for 
  ** pinned+dirty pages, and there is at least one dirty page,
  ** invoke the xStress callback to cause a page to become clean.
  */
  expensive_assert( pCache->nPinned==pcachePinnedCount(pCache) );
  expensive_assert( pcacheCheckSynced(pCache) );
  if( pCache->xStress
   && pCache->pDirty
   && (pCache->nPinned>=(pcache_g.nMaxPage+pCache->nMin-pcache_g.nMinPage)
           || pCache->nPinned>=pCache->nMax)
  ){
    PgHdr *pPg;
    assert(pCache->pDirtyTail);

    for(pPg=pCache->pSynced; 
        pPg && (pPg->nRef || (pPg->flags&PGHDR_NEED_SYNC)); 
        pPg=pPg->pPrev
    );
    if( !pPg ){
      for(pPg=pCache->pDirtyTail; pPg && pPg->nRef; pPg=pPg->pPrev);

    }
    if( pPg ){
      int rc;
      pcacheExitMutex();
      rc = pCache->xStress(pCache->pStress, pPg);
      pcacheEnterMutex();
      if( rc!=SQLITE_OK && rc!=SQLITE_BUSY ){
        return rc;
      }
    }
  }

  /* If either the local or the global page limit has been reached, 
  ** try to recycle a page. 
  */
  if( pCache->bPurgeable && (pCache->nPage>=pCache->nMax-1 ||
                             pcache_g.nCurrentPage>=pcache_g.nMaxPage) ){
    p = pcacheRecyclePage();
  }

  /* If a page has been recycled but it is the wrong size, free it. */
  if( p && (p->pCache->szPage!=szPage || p->pCache->szPage!=szExtra) ){
    pcachePageFree(p);
    p = 0;
  }

  if( !p ){
    p = pcachePageAlloc(pCache);
  }

  *ppPage = p;
  return (p?SQLITE_OK:SQLITE_NOMEM);
}

/*************************************************** General Interfaces ******
**
** Initialize and shutdown the page cache subsystem. Neither of these 
** functions are threadsafe.
*/
int sqlite3PcacheInitialize(void){
  assert( pcache_g.isInit==0 );
  memset(&pcache_g, 0, sizeof(pcache));
  if( sqlite3GlobalConfig.bCoreMutex ){
    /* No need to check the return value of sqlite3_mutex_alloc(). 
    ** Allocating a static mutex cannot fail.
    */
    pcache_g.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_LRU);

  }
  pcache_g.isInit = 1;
  return SQLITE_OK;

}
void sqlite3PcacheShutdown(void){
  memset(&pcache_g, 0, sizeof(pcache));



}

/*
** 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.


*/
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 */
){
  assert( pcache_g.isInit );
  memset(p, 0, sizeof(PCache));
  p->szPage = szPage;
  p->szExtra = szExtra;
  p->bPurgeable = bPurgeable;
  p->xStress = xStress;
  p->pStress = pStress;
  p->nMax = 100;
  p->nMin = 10;

  pcacheEnterMutex();
  if( bPurgeable ){
    pcache_g.nMaxPage += p->nMax;
    pcache_g.nMinPage += p->nMin;
  }

  pcacheExitMutex();
}

/*
** Change the page size for PCache object.  This can only happen
** when the cache is empty.
*/
void sqlite3PcacheSetPageSize(PCache *pCache, int szPage){



  assert(pCache->nPage==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 */
){
  int rc = SQLITE_OK;
  PgHdr *pPage = 0;

  assert( pcache_g.isInit );
  assert( pCache!=0 );
  assert( pgno>0 );
  expensive_assert( pCache->nPinned==pcachePinnedCount(pCache) );

  pcacheEnterMutex();

  /* Search the hash table for the requested page. Exit early if it is found. */
  if( pCache->apHash ){
    u32 h = pgno % pCache->nHash;
    for(pPage=pCache->apHash[h]; pPage; pPage=pPage->pNextHash){
      if( pPage->pgno==pgno ){
        if( pPage->nRef==0 ){
          if( 0==(pPage->flags&PGHDR_DIRTY) ){
            pcacheRemoveFromLruList(pPage);
            pCache->nPinned++;
          }
          pCache->nRef++;
        }
        pPage->nRef++;
        break;
      }
    }
  }

  if( !pPage && createFlag ){
    if( pCache->nHash<=pCache->nPage ){
      rc = pcacheResizeHash(pCache, pCache->nHash<256 ? 256 : pCache->nHash*2);
    }
    if( rc==SQLITE_OK ){
      rc = pcacheRecycleOrAlloc(pCache, &pPage);
    }
    if( rc==SQLITE_OK ){
      pPage->pPager = 0;
      pPage->flags = 0;
      pPage->pDirty = 0;
      pPage->pgno = pgno;
      pPage->pCache = pCache;
      pPage->nRef = 1;
      pCache->nRef++;
      pCache->nPinned++;
      pcacheAddToList(&pCache->pClean, pPage);
      pcacheAddToHash(pPage);
    }
  }

  pcacheExitMutex();

  *ppPage = pPage;
  expensive_assert( pCache->nPinned==pcachePinnedCount(pCache) );
  assert( pPage || !createFlag || rc!=SQLITE_OK );
  return rc;
















}

/*
** Dereference a page.  When the reference count reaches zero,
** move the page to the LRU list if it is clean.
*/
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 ){
      pCache->nPinned--;
      pcacheEnterMutex();
      if( pcache_g.nCurrentPage>pcache_g.nMaxPage ){
        pcacheRemoveFromList(&pCache->pClean, p);
        pcacheRemoveFromHash(p);
        pcachePageFree(p);
      }else{
        pcacheAddToLruList(p);
      }
      pcacheExitMutex();
    }else{
      /* Move the page to the head of the caches dirty list. */
      pcacheRemoveFromList(&pCache->pDirty, p);
      pcacheAddToList(&pCache->pDirty, p);
    }
  }
}




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 );
  assert( 0==(p->flags&PGHDR_DIRTY) );
  pCache = p->pCache;
  pCache->nRef--;
  pCache->nPinned--;
  pcacheEnterMutex();
  pcacheRemoveFromList(&pCache->pClean, p);
  pcacheRemoveFromHash(p);
  pcachePageFree(p);
  pcacheExitMutex();
}

/*
** Make sure the page is marked as dirty.  If it isn't dirty already,
** make it so.
*/
void sqlite3PcacheMakeDirty(PgHdr *p){
  PCache *pCache;
  p->flags &= ~PGHDR_DONT_WRITE;
  if( p->flags & PGHDR_DIRTY ) return;
  assert( (p->flags & PGHDR_DIRTY)==0 );
  assert( p->nRef>0 );

  pCache = p->pCache;
  pcacheEnterMutex();
  pcacheRemoveFromList(&pCache->pClean, p);
  pcacheAddToList(&pCache->pDirty, p);
  pcacheExitMutex();
  p->flags |= PGHDR_DIRTY;
}

static void pcacheMakeClean(PgHdr *p){
  PCache *pCache = p->pCache;
  assert( p->flags & PGHDR_DIRTY );
  pcacheRemoveFromList(&pCache->pDirty, p);
  pcacheAddToList(&pCache->pClean, p);
  p->flags &= ~PGHDR_DIRTY;
  if( p->nRef==0 ){
    pcacheAddToLruList(p);
    pCache->nPinned--;
  }
  expensive_assert( pCache->nPinned==pcachePinnedCount(pCache) );
}

/*
** 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) ){
    pcacheEnterMutex();
    pcacheMakeClean(p);

    pcacheExitMutex();

  }
}

/*
** Make every page in the cache clean.
*/
void sqlite3PcacheCleanAll(PCache *pCache){
  PgHdr *p;
  pcacheEnterMutex();
  while( (p = pCache->pDirty)!=0 ){
    pcacheRemoveFromList(&pCache->pDirty, p);
    p->flags &= ~PGHDR_DIRTY;
    pcacheAddToList(&pCache->pClean, p);
    if( p->nRef==0 ){
      pcacheAddToLruList(p);
      pCache->nPinned--;

    }
  }






  sqlite3PcacheAssertFlags(pCache, 0, PGHDR_DIRTY);
  expensive_assert( pCache->nPinned==pcachePinnedCount(pCache) );
  pcacheExitMutex();


}

/*
** Change the page number of page p to newPgno. If newPgno is 0, then the
** page object is added to the clean-list and the PGHDR_REUSE_UNLIKELY 
** flag set.
*/
void sqlite3PcacheMove(PgHdr *p, Pgno newPgno){

  assert( p->nRef>0 );

  pcacheEnterMutex();
  pcacheRemoveFromHash(p);
  p->pgno = newPgno;

  if( newPgno==0 ){
    if( (p->flags & PGHDR_DIRTY) ){
      pcacheMakeClean(p);
    }
    p->flags = PGHDR_REUSE_UNLIKELY;
  }
  pcacheAddToHash(p);
  pcacheExitMutex();
}

/*
** Remove all content from a page cache
*/
static void pcacheClear(PCache *pCache){
  PgHdr *p, *pNext;
  assert( sqlite3_mutex_held(pcache_g.mutex) );
  for(p=pCache->pClean; p; p=pNext){
    pNext = p->pNext;
    pcacheRemoveFromLruList(p);
    pcachePageFree(p);
  }
  for(p=pCache->pDirty; p; p=pNext){
    pNext = p->pNext;
    pcachePageFree(p);
  }
  pCache->pClean = 0;
  pCache->pDirty = 0;
  pCache->pDirtyTail = 0;
  pCache->nPage = 0;
  pCache->nPinned = 0;
  memset(pCache->apHash, 0, pCache->nHash*sizeof(pCache->apHash[0]));
}


/*
** Drop every cache entry whose page number is greater than "pgno".






*/
void sqlite3PcacheTruncate(PCache *pCache, Pgno pgno){

  PgHdr *p, *pNext;
  PgHdr *pDirty = pCache->pDirty;
  pcacheEnterMutex();
  for(p=pCache->pClean; p||pDirty; p=pNext){
    if( !p ){
      p = pDirty;
      pDirty = 0;
    }
    pNext = p->pNext;
    if( p->pgno>pgno ){
      if( p->nRef==0 ){
        pcacheRemoveFromHash(p);
        if( p->flags&PGHDR_DIRTY ){
          pcacheRemoveFromList(&pCache->pDirty, p);
          pCache->nPinned--;
        }else{
          pcacheRemoveFromList(&pCache->pClean, p);
          pcacheRemoveFromLruList(p);

        }
        pcachePageFree(p);
      }else{
        /* If there are references to the page, it cannot be freed. In this
        ** case, zero the page content instead.
        */
        memset(p->pData, 0, pCache->szPage);
      }



    }
  }
  pcacheExitMutex();
}

/*
** If there are currently more than pcache.nMaxPage pages allocated, try
** to recycle pages to reduce the number allocated to pcache.nMaxPage.
*/
static void pcacheEnforceMaxPage(void){
  PgHdr *p;
  assert( sqlite3_mutex_held(pcache_g.mutex) );
  while( pcache_g.nCurrentPage>pcache_g.nMaxPage
             && (p = pcacheRecyclePage())!=0 ){
    pcachePageFree(p);

  }
}

/*
** Close a cache.
*/
void sqlite3PcacheClose(PCache *pCache){
  pcacheEnterMutex();

  /* Free all the pages used by this pager and remove them from the LRU list. */
  pcacheClear(pCache);
  if( pCache->bPurgeable ){
    pcache_g.nMaxPage -= pCache->nMax;
    pcache_g.nMinPage -= pCache->nMin;
    pcacheEnforceMaxPage();

  }
  sqlite3_free(pCache->apHash);
  pcacheExitMutex();
}


#ifndef NDEBUG
/* 
** Assert flags settings on all pages.  Debugging only.
*/
void sqlite3PcacheAssertFlags(PCache *pCache, int trueMask, int falseMask){
  PgHdr *p;
  for(p=pCache->pDirty; p; p=p->pNext){
    assert( (p->flags&trueMask)==trueMask );
    assert( (p->flags&falseMask)==0 );
  }
  for(p=pCache->pClean; p; p=p->pNext){
    assert( (p->flags&trueMask)==trueMask );
    assert( (p->flags&falseMask)==0 );
  }
}
#endif

/* 
** Discard the contents of the cache.
*/
int sqlite3PcacheClear(PCache *pCache){
  assert(pCache->nRef==0);
  pcacheEnterMutex();
  pcacheClear(pCache);
  pcacheExitMutex();
  return SQLITE_OK;
}

/*
** Merge two lists of pages connected by pDirty and in pgno order.
** Do not both fixing the pPrevDirty 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->pDirty = 0;
  }
  return result.pDirty;
}

/*
** Sort the list of pages in accending order by pgno.  Pages are
** connected by pDirty pointers.  The pPrevDirty pointers are
** corrupted by this sort.
*/
#define N_SORT_BUCKET_ALLOC 25
#define N_SORT_BUCKET       25
#ifdef SQLITE_TEST
  int sqlite3_pager_n_sort_bucket = 0;
  #undef N_SORT_BUCKET
................................................................................
}

/*
** 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->pNext){
    p->pDirty = p->pNext;
  }
  return pcacheSortDirtyList(pCache->pDirty);
}

/* 
** Return the total number of outstanding page references.
*/
int sqlite3PcacheRefCount(PCache *pCache){
  return pCache->nRef;
}




int sqlite3PcachePageRefcount(PgHdr *p){
  return p->nRef;
}

/* 
** Return the total number of pages in the cache.
*/
int sqlite3PcachePagecount(PCache *pCache){
  assert( pCache->nPage>=0 );
  return pCache->nPage;

}

#ifdef SQLITE_CHECK_PAGES
/*
** This function is used by the pager.c module to iterate through all 
** pages in the cache. At present, this is only required if the
** SQLITE_CHECK_PAGES macro (used for debugging) is specified.
*/
void sqlite3PcacheIterate(PCache *pCache, void (*xIter)(PgHdr *)){
  PgHdr *p;
  for(p=pCache->pClean; p; p=p->pNext){
    xIter(p);
  }
  for(p=pCache->pDirty; p; p=p->pNext){
    xIter(p);
  }
}
#endif

/* 
** Set flags on all pages in the page cache 
*/
void sqlite3PcacheClearFlags(PCache *pCache, int mask){
  PgHdr *p;

  /* Obtain the global mutex before modifying any PgHdr.flags variables 
  ** or traversing the LRU list.
  */ 
  pcacheEnterMutex();

  mask = ~mask;
  for(p=pCache->pDirty; p; p=p->pNext){
    p->flags &= mask;
  }
  for(p=pCache->pClean; p; p=p->pNext){
    p->flags &= mask;
  }

  if( 0==(mask&PGHDR_NEED_SYNC) ){
    pCache->pSynced = pCache->pDirtyTail;
    assert( !pCache->pSynced || (pCache->pSynced->flags&PGHDR_NEED_SYNC)==0 );
  }

  pcacheExitMutex();
}

/*
** Set the suggested cache-size value.
*/
int sqlite3PcacheGetCachesize(PCache *pCache){
  return pCache->nMax;
}

/*
** Set the suggested cache-size value.
*/
void sqlite3PcacheSetCachesize(PCache *pCache, int mxPage){
  if( mxPage<10 ){
    mxPage = 10;
  }
  if( pCache->bPurgeable ){
    pcacheEnterMutex();
    pcache_g.nMaxPage -= pCache->nMax;
    pcache_g.nMaxPage += mxPage;
    pcacheEnforceMaxPage();
    pcacheExitMutex();

  }
  pCache->nMax = mxPage;
}

#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( pcache_g.pStart==0 ){
    PgHdr *p;
    pcacheEnterMutex();
    while( (nReq<0 || nFree<nReq) && (p=pcacheRecyclePage()) ){
      nFree += pcachePageSize(p);
      pcachePageFree(p);
    }
    pcacheExitMutex();
  }
  return nFree;
}
#endif /* SQLITE_ENABLE_MEMORY_MANAGEMENT */

#ifdef SQLITE_TEST
void sqlite3PcacheStats(
  int *pnCurrent,
  int *pnMax,
  int *pnMin,
  int *pnRecyclable
){
  PgHdr *p;
  int nRecyclable = 0;
  for(p=pcache_g.pLruHead; p; p=p->pNextLru){
    nRecyclable++;


  }

  *pnCurrent = pcache_g.nCurrentPage;
  *pnMax = pcache_g.nMaxPage;
  *pnMin = pcache_g.nMinPage;
  *pnRecyclable = nRecyclable;
}
#endif








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**    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.
**
** @(#) $Id: pcache.c,v 1.37 2008/11/13 14:28:29 danielk1977 Exp $
*/
#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 nMin;                           /* Configured minimum 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;







};






















































/*
** 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 ){




    sqlite3PCacheSetDefault();
  }


  return sqlite3GlobalConfig.pcache.xInit(sqlite3GlobalConfig.pcache.pArg);
}
void sqlite3PcacheShutdown(void){

  if( sqlite3GlobalConfig.pcache.xShutdown ){
    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;
  p->nMin = 10;








}

/*
** 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->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( 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 : 0;
  if( eCreate && (!pCache->bPurgeable || !pCache->pDirty) ){
    eCreate = 2;
  }
  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
    );
    if( !pPg ){
      for(pPg=pCache->pDirtyTail; pPg && pPg->nRef; pPg=pPg->pDirtyPrev);
    }
    if( pPg ){
      int rc;
      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( 0==pPage->nRef ){
      pCache->nRef++;
    }
    pPage->nRef++;
    pPage->pData = (void*)&pPage[1];
    pPage->pExtra = (void*)&((char*)pPage->pData)[pCache->szPage];
    pPage->pCache = pCache;
    pPage->pgno = pgno;
    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){
  PCache *pCache;
  p->flags &= ~PGHDR_DONT_WRITE;


  assert( p->nRef>0 );
  if( 0==(p->flags & PGHDR_DIRTY) ){
    pCache = p->pCache;




    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;
      if( 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.
*/
int sqlite3PcacheClear(PCache *pCache){
  sqlite3PcacheTruncate(pCache, 0);



  return SQLITE_OK;
}

/*
** 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->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.
*/
#define N_SORT_BUCKET_ALLOC 25
#define N_SORT_BUCKET       25
#ifdef SQLITE_TEST
  int sqlite3_pager_n_sort_bucket = 0;
  #undef N_SORT_BUCKET
................................................................................
}

/*
** 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;









}






/*



























** Get the suggested cache-size value.
*/
int sqlite3PcacheGetCachesize(PCache *pCache){
  return pCache->nMax;
}

/*
** Set the suggested cache-size value.
*/
void sqlite3PcacheSetCachesize(PCache *pCache, int mxPage){
  pCache->nMax = mxPage;


  if( pCache->pCache ){





    sqlite3GlobalConfig.pcache.xCachesize(pCache->pCache, mxPage);
  }

}

#ifdef SQLITE_CHECK_PAGES
/*







** 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

Changes to src/pcache.h.

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**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite page cache
** subsystem. 
**
** @(#) $Id: pcache.h,v 1.14 2008/10/17 18:51:53 danielk1977 Exp $
*/

#ifndef _PCACHE_H_

typedef struct PgHdr PgHdr;
typedef struct PCache PCache;

................................................................................
  PgHdr *pDirty;                 /* Transient list of dirty pages */
  Pgno pgno;                     /* Page number for this page */
  Pager *pPager;                 /* The pager this page is part of */
#ifdef SQLITE_CHECK_PAGES
  u32 pageHash;                  /* Hash of page content */
#endif
  u16 flags;                     /* PGHDR flags defined below */

  /**********************************************************************
  ** Elements above are public.  All that follows is private to pcache.c
  ** and should not be accessed by other modules.
  */
  i16 nRef;                      /* Number of users of this page */
  PCache *pCache;                /* Cache that owns this page */

  /**********************************************************************
  ** Elements above are accessible at any time by the owner of the cache
  ** without the need for a mutex.  The elements that follow can only be
  ** accessed while holding the SQLITE_MUTEX_STATIC_LRU mutex.
  */
  PgHdr *pNextHash, *pPrevHash;  /* Hash collision chain for PgHdr.pgno */
  PgHdr *pNext, *pPrev;          /* List of clean or dirty pages */
  PgHdr *pNextLru, *pPrevLru;    /* Part of global LRU list */
};

/* Bit values for PgHdr.flags */
#define PGHDR_IN_JOURNAL        0x001  /* Page is in rollback journal */
#define PGHDR_DIRTY             0x002  /* Page has changed */
#define PGHDR_NEED_SYNC         0x004  /* Fsync the rollback journal before
                                       ** writing this page to the database */
#define PGHDR_NEED_READ         0x008  /* Content is unread */
#define PGHDR_REUSE_UNLIKELY    0x010  /* A hint that reuse is unlikely */
#define PGHDR_DONT_WRITE        0x020  /* Do not write content to disk */

................................................................................
/* Get a list of all dirty pages in the cache, sorted by page number */
PgHdr *sqlite3PcacheDirtyList(PCache*);

/* Reset and close the cache object */
void sqlite3PcacheClose(PCache*);

/* Clear flags from pages of the page cache */
void sqlite3PcacheClearFlags(PCache*, int mask);

/* Assert flags settings on all pages.  Debugging only */
#ifndef NDEBUG
  void sqlite3PcacheAssertFlags(PCache*, int trueMask, int falseMask);
#else
# define sqlite3PcacheAssertFlags(A,B,C)
#endif

/* Return true if the number of dirty pages is 0 or 1 */
int sqlite3PcacheZeroOrOneDirtyPages(PCache*);

/* Discard the contents of the cache */
int sqlite3PcacheClear(PCache*);

................................................................................

int sqlite3PcachePageRefcount(PgHdr*);

/* Return the total number of pages stored in the cache */
int sqlite3PcachePagecount(PCache*);

#ifdef SQLITE_CHECK_PAGES
/* Iterate through all pages currently stored in the cache. This interface
** is only available if SQLITE_CHECK_PAGES is defined when the library is 
** built.
*/
void sqlite3PcacheIterate(PCache *pCache, void (*xIter)(PgHdr *));
#endif

/* Set and get the suggested cache-size for the specified pager-cache.
**
** If no global maximum is configured, then the system attempts to limit
** the total number of pages cached by purgeable pager-caches to the sum
** of the suggested cache-sizes.
................................................................................
/* Try to return memory used by the pcache module to the main memory heap */
int sqlite3PcacheReleaseMemory(int);
#endif

#ifdef SQLITE_TEST
void sqlite3PcacheStats(int*,int*,int*,int*);
#endif



#endif /* _PCACHE_H_ */







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**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite page cache
** subsystem. 
**
** @(#) $Id: pcache.h,v 1.15 2008/11/13 14:28:29 danielk1977 Exp $
*/

#ifndef _PCACHE_H_

typedef struct PgHdr PgHdr;
typedef struct PCache PCache;

................................................................................
  PgHdr *pDirty;                 /* Transient list of dirty pages */
  Pgno pgno;                     /* Page number for this page */
  Pager *pPager;                 /* The pager this page is part of */
#ifdef SQLITE_CHECK_PAGES
  u32 pageHash;                  /* Hash of page content */
#endif
  u16 flags;                     /* PGHDR flags defined below */

  /**********************************************************************
  ** Elements above are public.  All that follows is private to pcache.c
  ** and should not be accessed by other modules.
  */
  i16 nRef;                      /* Number of users of this page */
  PCache *pCache;                /* Cache that owns this page */

  PgHdr *pDirtyNext;             /* Next element in list of dirty pages */
  PgHdr *pDirtyPrev;             /* Previous element in list of dirty pages */






};

/* Bit values for PgHdr.flags */

#define PGHDR_DIRTY             0x002  /* Page has changed */
#define PGHDR_NEED_SYNC         0x004  /* Fsync the rollback journal before
                                       ** writing this page to the database */
#define PGHDR_NEED_READ         0x008  /* Content is unread */
#define PGHDR_REUSE_UNLIKELY    0x010  /* A hint that reuse is unlikely */
#define PGHDR_DONT_WRITE        0x020  /* Do not write content to disk */

................................................................................
/* Get a list of all dirty pages in the cache, sorted by page number */
PgHdr *sqlite3PcacheDirtyList(PCache*);

/* Reset and close the cache object */
void sqlite3PcacheClose(PCache*);

/* Clear flags from pages of the page cache */
void sqlite3PcacheClearSyncFlags(PCache *);








/* Return true if the number of dirty pages is 0 or 1 */
int sqlite3PcacheZeroOrOneDirtyPages(PCache*);

/* Discard the contents of the cache */
int sqlite3PcacheClear(PCache*);

................................................................................

int sqlite3PcachePageRefcount(PgHdr*);

/* Return the total number of pages stored in the cache */
int sqlite3PcachePagecount(PCache*);

#ifdef SQLITE_CHECK_PAGES
/* Iterate through all dirty pages currently stored in the cache. This
** interface is only available if SQLITE_CHECK_PAGES is defined when the 
** library is built.
*/
void sqlite3PcacheIterateDirty(PCache *pCache, void (*xIter)(PgHdr *));
#endif

/* Set and get the suggested cache-size for the specified pager-cache.
**
** If no global maximum is configured, then the system attempts to limit
** the total number of pages cached by purgeable pager-caches to the sum
** of the suggested cache-sizes.
................................................................................
/* Try to return memory used by the pcache module to the main memory heap */
int sqlite3PcacheReleaseMemory(int);
#endif

#ifdef SQLITE_TEST
void sqlite3PcacheStats(int*,int*,int*,int*);
#endif

void sqlite3PCacheSetDefault(void);

#endif /* _PCACHE_H_ */

Added src/pcache1.c.































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































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/*
** 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 1.1 2008/11/13 14:28:29 danielk1977 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 */
  int nMin;                           /* Minimum number of pages reserved */
  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()).
  */
  int nRecyclable;                    /* Number of pages in the LRU list */
  int nPage;                          /* Total number of pages in apHash */
  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 = {0};

/*
** 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*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;
  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 *pUnused){
  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 *pUnused){
  /* 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){
  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

Changes to src/sqlite.h.in.

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** on how SQLite interfaces are suppose to operate.
**
** The name of this file under configuration management is "sqlite.h.in".
** The makefile makes some minor changes to this file (such as inserting
** the version number) and changes its name to "sqlite3.h" as
** part of the build process.
**
** @(#) $Id: sqlite.h.in,v 1.412 2008/11/10 23:54:06 drh Exp $
*/
#ifndef _SQLITE3_H_
#define _SQLITE3_H_
#include <stdarg.h>     /* Needed for the definition of va_list */

/*
** Make sure we can call this stuff from C++.
................................................................................
#define SQLITE_CONFIG_PAGECACHE     7  /* void*, int sz, int N */
#define SQLITE_CONFIG_HEAP          8  /* void*, int nByte, int min */
#define SQLITE_CONFIG_MEMSTATUS     9  /* boolean */
#define SQLITE_CONFIG_MUTEX        10  /* sqlite3_mutex_methods* */
#define SQLITE_CONFIG_GETMUTEX     11  /* sqlite3_mutex_methods* */
/* previously SQLITE_CONFIG_CHUNKALLOC 12 which is now unused. */ 
#define SQLITE_CONFIG_LOOKASIDE    13  /* int int */



/*
** CAPI3REF: Configuration Options {H10170} <S20000>
** EXPERIMENTAL
**
** These constants are the available integer configuration options that
** can be passed as the second argument to the [sqlite3_db_config()] interface.
................................................................................
** A non-zero value in this counter may indicate an opportunity to
** improvement performance through careful use of indices.</dd>
**
** </dl>
*/
#define SQLITE_STMTSTATUS_FULLSCAN_STEP     1
#define SQLITE_STMTSTATUS_SORT              2

/*









































































































































** Undo the hack that converts floating point types to integer for
** builds on processors without floating point support.
*/
#ifdef SQLITE_OMIT_FLOATING_POINT
# undef double
#endif

#ifdef __cplusplus
}  /* End of the 'extern "C"' block */
#endif
#endif







|







 







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** on how SQLite interfaces are suppose to operate.
**
** The name of this file under configuration management is "sqlite.h.in".
** The makefile makes some minor changes to this file (such as inserting
** the version number) and changes its name to "sqlite3.h" as
** part of the build process.
**
** @(#) $Id: sqlite.h.in,v 1.413 2008/11/13 14:28:29 danielk1977 Exp $
*/
#ifndef _SQLITE3_H_
#define _SQLITE3_H_
#include <stdarg.h>     /* Needed for the definition of va_list */

/*
** Make sure we can call this stuff from C++.
................................................................................
#define SQLITE_CONFIG_PAGECACHE     7  /* void*, int sz, int N */
#define SQLITE_CONFIG_HEAP          8  /* void*, int nByte, int min */
#define SQLITE_CONFIG_MEMSTATUS     9  /* boolean */
#define SQLITE_CONFIG_MUTEX        10  /* sqlite3_mutex_methods* */
#define SQLITE_CONFIG_GETMUTEX     11  /* sqlite3_mutex_methods* */
/* previously SQLITE_CONFIG_CHUNKALLOC 12 which is now unused. */ 
#define SQLITE_CONFIG_LOOKASIDE    13  /* int int */
#define SQLITE_CONFIG_PCACHE       14  /* sqlite3_pcache_methods* */
#define SQLITE_CONFIG_GETPCACHE    15  /* sqlite3_pcache_methods* */

/*
** CAPI3REF: Configuration Options {H10170} <S20000>
** EXPERIMENTAL
**
** These constants are the available integer configuration options that
** can be passed as the second argument to the [sqlite3_db_config()] interface.
................................................................................
** A non-zero value in this counter may indicate an opportunity to
** improvement performance through careful use of indices.</dd>
**
** </dl>
*/
#define SQLITE_STMTSTATUS_FULLSCAN_STEP     1
#define SQLITE_STMTSTATUS_SORT              2

/*
** The sqlite3_pcache type is opaque.  It is implemented by
** the pluggable module.  The SQLite core has no knowledge of
** its size or internal structure and never deals with the
** sqlite3_pcache object except by holding and passing pointers
** to the object.
*/
typedef struct sqlite3_pcache sqlite3_pcache;

/*
** CAPI3REF: Custom Page Cache API.
** EXPERIMENTAL
**
** The sqlite3_config(SQLITE_CONFIG_SET_PCACHE, ...) interface can
** register an alternative page cache implementation by passing in an 
** instance of the sqlite3_pcache_methods structure. The majority of the 
** heap memory used by sqlite is used by the page cache to cache data read 
** from, or ready to be written to, the database file. By implementing a 
** custom page cache using this API, an application can control more 
** precisely the amount of memory consumed by sqlite, the way in which 
** said memory is allocated and released, and the policies used to 
** determine exactly which parts of a database file are cached and for 
** how long.
**
** The contents of the structure are copied to an internal buffer by sqlite
** within the call to [sqlite3_config].
**
** The xInit() method is called once for each call to sqlite3_initialize()
** (usually only once during the lifetime of the process). It is passed
** a copy of the sqlite3_pcache_methods.pArg value. It can be used to set
** up global structures and mutexes required by the custom page cache 
** implementation. The xShutdown() method is called from within 
** sqlite3_shutdown(), if the application invokes this API. It can be used
** to clean up any outstanding resources before process shutdown, if required.
**
** The xCreate() method is used to construct a new cache instance. The
** first parameter, szPage, is the size in bytes of the pages that must
** be allocated by the cache. szPage will not be a power of two. The
** second argument, bPurgeable, is true if the cache being created will
** be used to cache database pages read from a file stored on disk, or
** false if it is used for an in-memory database. The cache implementation
** does not have to do anything special based on the value of bPurgeable,
** it is purely advisory. 
**
** The xCachesize() method may be called at any time by SQLite to set the
** suggested maximum cache-size (number of pages stored by) the cache
** instance passed as the first argument. This is the value configured using
** the SQLite "PRAGMA cache_size" command. As with the bPurgeable parameter,
** the implementation is not required to do anything special with this
** value, it is advisory only.
**
** The xPagecount() method should return the number of pages currently
** stored in the cache supplied as an argument.
** 
** The xFetch() method is used to fetch a page and return a pointer to it. 
** A 'page', in this context, is a buffer of szPage bytes aligned at an
** 8-byte boundary. The page to be fetched is determined by the key. The
** mimimum key value is 1. After it has been retrieved using xFetch, the page 
** is considered to be pinned.
**
** If the requested page is already in the page cache, then a pointer to
** the cached buffer should be returned with its contents intact. If the
** page is not already in the cache, then the expected behaviour of the
** cache is determined by the value of the createFlag parameter passed
** to xFetch, according to the following table:
**
** <table border=1 width=85% align=center>
**   <tr><th>createFlag<th>Expected Behaviour
**   <tr><td>0<td>NULL should be returned. No new cache entry is created.
**   <tr><td>1<td>If createFlag is set to 1, this indicates that 
**                SQLite is holding pinned pages that can be unpinned
**                by writing their contents to the database file (a
**                relatively expensive operation). In this situation the
**                cache implementation has two choices: it can return NULL,
**                in which case SQLite will attempt to unpin one or more 
**                pages before re-requesting the same page, or it can
**                allocate a new page and return a pointer to it. If a new
**                page is allocated, then it must be completely zeroed before 
**                it is returned.
**   <tr><td>2<td>If createFlag is set to 2, then SQLite is not holding any
**                pinned pages associated with the specific cache passed
**                as the first argument to xFetch() that can be unpinned. The
**                cache implementation should attempt to allocate a new
**                cache entry and return a pointer to it. Again, the new
**                page should be zeroed before it is returned. If the xFetch()
**                method returns NULL when createFlag==2, SQLite assumes that
**                a memory allocation failed and returns SQLITE_NOMEM to the
**                user.
** </table>
**
** xUnpin() is called by SQLite with a pointer to a currently pinned page
** as its second argument. If the third parameter, discard, is non-zero,
** then the page should be evicted from the cache. In this case SQLite 
** assumes that the next time the page is retrieved from the cache using
** the xFetch() method, it will be zeroed. If the discard parameter is
** zero, then the page is considered to be unpinned. The cache implementation
** may choose to reclaim (free or recycle) unpinned pages at any time.
** SQLite assumes that next time the page is retrieved from the cache
** it will either be zeroed, or contain the same data that it did when it
** was unpinned.
**
** The cache is not required to perform any reference counting. A single 
** call to xUnpin() unpins the page regardless of the number of prior calls 
** to xFetch().
**
** The xRekey() method is used to change the key value associated with the
** page passed as the second argument from oldKey to newKey. If the cache
** contains an entry associated with oldKey, it should be discarded. Any
** cache entry associated with oldKey is guaranteed not to be pinned.
**
** When SQLite calls the xTruncate() method, the cache must discard all
** existing cache entries with page numbers (keys) greater than or equal
** to the value of the iLimit parameter passed to xTruncate(). If any
** of these pages are pinned, they are implicitly unpinned, meaning that
** they can be safely discarded.
**
** 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.
*/
typedef struct sqlite3_pcache_methods sqlite3_pcache_methods;
struct sqlite3_pcache_methods {
  void *pArg;
  int (*xInit)(void*);
  void (*xShutdown)(void*);
  sqlite3_pcache *(*xCreate)(int szPage, int bPurgeable);
  void (*xCachesize)(sqlite3_pcache*, int nCachesize);
  int (*xPagecount)(sqlite3_pcache*);
  void *(*xFetch)(sqlite3_pcache*, unsigned key, int createFlag);
  void (*xUnpin)(sqlite3_pcache*, void*, int discard);
  void (*xRekey)(sqlite3_pcache*, void*, unsigned oldKey, unsigned newKey);
  void (*xTruncate)(sqlite3_pcache*, unsigned iLimit);
  void (*xDestroy)(sqlite3_pcache*);
};

/*
** Undo the hack that converts floating point types to integer for
** builds on processors without floating point support.
*/
#ifdef SQLITE_OMIT_FLOATING_POINT
# undef double
#endif

#ifdef __cplusplus
}  /* End of the 'extern "C"' block */
#endif
#endif

Changes to src/sqliteInt.h.

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**    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.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.790 2008/11/11 18:29:00 drh Exp $
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_

/*
** Include the configuration header output by 'configure' if we're using the
** autoconf-based build
................................................................................
  int bCoreMutex;                   /* True to enable core mutexing */
  int bFullMutex;                   /* True to enable full mutexing */
  int mxStrlen;                     /* Maximum string length */
  int szLookaside;                  /* Default lookaside buffer size */
  int nLookaside;                   /* Default lookaside buffer count */
  sqlite3_mem_methods m;            /* Low-level memory allocation interface */
  sqlite3_mutex_methods mutex;      /* Low-level mutex interface */

  void *pHeap;                      /* Heap storage space */
  int nHeap;                        /* Size of pHeap[] */
  int mnReq, mxReq;                 /* Min and max heap requests sizes */
  void *pScratch;                   /* Scratch memory */
  int szScratch;                    /* Size of each scratch buffer */
  int nScratch;                     /* Number of scratch buffers */
  void *pPage;                      /* Page cache memory */







|







 







>







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**    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.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.791 2008/11/13 14:28:30 danielk1977 Exp $
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_

/*
** Include the configuration header output by 'configure' if we're using the
** autoconf-based build
................................................................................
  int bCoreMutex;                   /* True to enable core mutexing */
  int bFullMutex;                   /* True to enable full mutexing */
  int mxStrlen;                     /* Maximum string length */
  int szLookaside;                  /* Default lookaside buffer size */
  int nLookaside;                   /* Default lookaside buffer count */
  sqlite3_mem_methods m;            /* Low-level memory allocation interface */
  sqlite3_mutex_methods mutex;      /* Low-level mutex interface */
  sqlite3_pcache_methods pcache;    /* Low-level page-cache interface */
  void *pHeap;                      /* Heap storage space */
  int nHeap;                        /* Size of pHeap[] */
  int mnReq, mxReq;                 /* Min and max heap requests sizes */
  void *pScratch;                   /* Scratch memory */
  int szScratch;                    /* Size of each scratch buffer */
  int nScratch;                     /* Number of scratch buffers */
  void *pPage;                      /* Page cache memory */