SQLite

** 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 1.490 2008/09/16 05:12:24 danielk1977 Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"

/*
** Macros for troubleshooting.  Normally turned off
*/

    pPager->pInJournal = 0;
    sqlite3BitvecDestroy(pPager->pAlwaysRollback);
    pPager->pAlwaysRollback = 0;
    sqlite3PcacheCleanAll(pPager->pPCache);
#ifdef SQLITE_CHECK_PAGES
    sqlite3PcacheIterate(pPager->pPCache, pager_set_pagehash);
#endif
    sqlite3PcacheSetFlags(pPager->pPCache,
       ~(PGHDR_IN_JOURNAL | PGHDR_NEED_SYNC), 0
    );
    pPager->dirtyCache = 0;
    pPager->nRec = 0;
  }else{
    assert( pPager->pInJournal==0 );
  }

**              point of causing damage to the database during rollback.
**
** Numeric values associated with these states are OFF==1, NORMAL=2,
** and FULL=3.
*/
#ifndef SQLITE_OMIT_PAGER_PRAGMAS
void sqlite3PagerSetSafetyLevel(Pager *pPager, int level, int bFullFsync){
  pPager->noSync =  level==1 || pPager->tempFile;
  pPager->fullSync = level==3 && !pPager->tempFile;
  pPager->sync_flags = (bFullFsync?SQLITE_SYNC_FULL:SQLITE_SYNC_NORMAL);
  if( pPager->noSync ) pPager->needSync = 0;
}
#endif

/*

    if( zPathname==0 ){
      return SQLITE_NOMEM;
    }
#ifndef SQLITE_OMIT_MEMORYDB
    if( strcmp(zFilename,":memory:")==0 ){
      memDb = 1;
      zPathname[0] = 0;

    }else
#endif
    {
      rc = sqlite3OsFullPathname(pVfs, zFilename, nPathname, zPathname);
    }
    if( rc!=SQLITE_OK ){
      sqlite3_free(zPathname);

    memcpy(pPager->zJournal, pPager->zFilename, nPathname);
    memcpy(&pPager->zJournal[nPathname], "-journal", 9);
  }else{
    pPager->zJournal = 0;
  }

  /* pPager->journalOpen = 0; */
  pPager->useJournal = useJournal && !memDb;
  pPager->noReadlock = noReadlock && readOnly;
  /* pPager->stmtOpen = 0; */
  /* pPager->stmtInUse = 0; */
  /* pPager->nRef = 0; */
  pPager->dbSize = memDb-1;
  pPager->pageSize = szPageDflt;
  /* pPager->stmtSize = 0; */

      }
      pPager->journalStarted = 1;
    }
    pPager->needSync = 0;

    /* Erase the needSync flag from every page.
    */
    sqlite3PcacheSetFlags(pPager->pPCache, ~PGHDR_NEED_SYNC, 0);
    /* lruListSetFirstSynced(pPager); */
  }

#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);
    /* assert( pPager->lru.pFirstSynced==pPager->lru.pFirst ); */
  }
#endif

  return rc;
}

/*

      PAGERTRACE3("NOSTORE %d page %d\n", PAGERID(pPager), pList->pgno);
    }
#endif
    if( rc ) return rc;
#ifdef SQLITE_CHECK_PAGES
    pList->pageHash = pager_pagehash(pList);
#endif
    /* makeClean(pList); */
    pList = pList->pDirty;
  }

  /* sqlite3PcacheCleanAll(pPager->pPCache); */
  return SQLITE_OK;
}

/*
** This function is called by the pcache layer when it has reached some
** soft memory limit. The argument is a pointer to a purgeable Pager 
** object. This function attempts to make a single dirty page that has no

    /* 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);

    /* If the PgHdr.needSync flag is set for any of the nPage pages 
    ** starting at pg1, then it needs to be set for all of them. Because
    ** writing to any of these nPage pages may damage the others, the
    ** journal file must contain sync()ed copies of all of them
    ** before any of them can be written out to the database file.
    */
    if( needSync ){

      for(ii=0; ii<nPage && needSync; ii++){
        PgHdr *pPage = pager_lookup(pPager, pg1+ii);
        if( pPage ) pPage->flags |= PGHDR_NEED_SYNC;
        sqlite3PagerUnref(pPage);
      }
      assert(pPager->needSync);
    }

    assert( pPager->dirtyCache==0 || pPager->journalOpen==0 );
    return SQLITE_OK;
  }
  PAGERTRACE2("COMMIT %d\n", PAGERID(pPager));
  if( MEMDB ){
    sqlite3PcacheCommit(pPager->pPCache, 0);
    sqlite3PcacheCleanAll(pPager->pPCache);
    sqlite3PcacheSetFlags(pPager->pPCache, 
       ~(PGHDR_IN_JOURNAL | PGHDR_NEED_SYNC), 0
    );
    pPager->state = PAGER_SHARED;
  }else{
    assert( pPager->state==PAGER_SYNCED || !pPager->dirtyCache );
    rc = pager_end_transaction(pPager, pPager->setMaster);
    rc = pager_error(pPager, rc);
  }
  return rc;

int sqlite3PagerRollback(Pager *pPager){
  int rc = SQLITE_OK;
  PAGERTRACE2("ROLLBACK %d\n", PAGERID(pPager));
  if( MEMDB ){
    sqlite3PcacheRollback(pPager->pPCache, 1);
    sqlite3PcacheRollback(pPager->pPCache, 0);
    sqlite3PcacheCleanAll(pPager->pPCache);
    sqlite3PcacheSetFlags(pPager->pPCache, 
       ~(PGHDR_IN_JOURNAL | PGHDR_NEED_SYNC), 0
    );
    pPager->dbSize = pPager->origDbSize;
    pager_truncate_cache(pPager);
    pPager->stmtInUse = 0;
    pPager->state = PAGER_SHARED;
  }else if( !pPager->dirtyCache || !pPager->journalOpen ){
    rc = pager_end_transaction(pPager, pPager->setMaster);
  }else if( pPager->errCode && pPager->errCode!=SQLITE_FULL ){

/*
** Commit a statement.
*/
int sqlite3PagerStmtCommit(Pager *pPager){
  if( pPager->stmtInUse ){
    PAGERTRACE2("STMT-COMMIT %d\n", PAGERID(pPager));
    if( !MEMDB ){
      /* sqlite3OsTruncate(pPager->stfd, 0); */
      sqlite3BitvecDestroy(pPager->pInStmt);
      pPager->pInStmt = 0;
    }else{
      sqlite3PcacheCommit(pPager->pPCache, 1);
    }
    pPager->stmtNRec = 0;
    pPager->stmtInUse = 0;

#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** Move the page pPg to location pgno in the file.
**
** There must be no references to the page previously located at
** pgno (which we call pPgOld) though that page is allowed to be
** in cache.  If the page previous located at pgno is not already
** in the rollback journal, it is not put there by by this routine.
**
** References to the page pPg remain valid. Updating any
** meta-data associated with pPg (i.e. data stored in the nExtra bytes
** allocated along with the page) is the responsibility of the caller.
**
** A transaction must be active when this routine is called. It used to be

  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);

    if( rc!=SQLITE_OK ){
      if( pPager->pInJournal && (int)needSyncPgno<=pPager->origDbSize ){
        sqlite3BitvecClear(pPager->pInJournal, needSyncPgno);
      }
      return rc;
    }
    pPager->needSync = 1;

    pPgHdr->flags |= PGHDR_NEED_SYNC;
    pPgHdr->flags |= PGHDR_IN_JOURNAL;
    makeDirty(pPgHdr);
    sqlite3PagerUnref(pPgHdr);
  }

  return SQLITE_OK;

/*
** 2008 August 05
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file implements that page cache.
**
** @(#) $Id: pcache.c,v 1.28 2008/09/17 11:02:57 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

*/
void sqlite3PcacheMove(PgHdr *p, Pgno newPgno){
  assert( p->nRef>0 );
  pcacheEnterMutex();
  pcacheRemoveFromHash(p);
  p->pgno = newPgno;
  if( newPgno==0 ){
    p->flags |= PGHDR_REUSE_UNLIKELY;
    pcacheFree(p->apSave[0]);
    pcacheFree(p->apSave[1]);
    p->apSave[0] = 0;
    p->apSave[1] = 0;
    if( (p->flags & PGHDR_DIRTY) ){
      pcacheMakeClean(p);
    }

  }
  pcacheAddToHash(p);
  pcacheExitMutex();
}

/*
** Remove all content from a page cache

}

/*
** Commit a change previously preserved.
*/
void sqlite3PcacheCommit(PCache *pCache, int idJournal){
  PgHdr *p;

  pcacheEnterMutex();     /* Mutex is required to call pcacheFree() */
  for(p=pCache->pDirty; p; p=p->pNext){
    if( p->apSave[idJournal] ){
      pcacheFree(p->apSave[idJournal]);
      p->apSave[idJournal] = 0;
    }

  }
  pcacheExitMutex();
}

/*
** Rollback a change previously preserved.
*/
void sqlite3PcacheRollback(PCache *pCache, int idJournal){
  PgHdr *p;
  int sz;

  pcacheEnterMutex();     /* Mutex is required to call pcacheFree() */
  sz = pCache->szPage;
  for(p=pCache->pDirty; p; p=p->pNext){
    if( p->apSave[idJournal] ){
      memcpy(p->pData, p->apSave[idJournal], sz);
      pcacheFree(p->apSave[idJournal]);
      p->apSave[idJournal] = 0;
    }

  }
  pcacheExitMutex();
}


/* 
** 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 );
  }
}


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

  }
}
#endif

/* 
** Set flags on all pages in the page cache 
*/
void sqlite3PcacheSetFlags(PCache *pCache, int andMask, int orMask){
  PgHdr *p;

  assert( (orMask&PGHDR_NEED_SYNC)==0 );

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


  for(p=pCache->pDirty; p; p=p->pNext){
    p->flags = (p->flags&andMask)|orMask;
  }
  for(p=pCache->pClean; p; p=p->pNext){
    p->flags = (p->flags&andMask)|orMask;
  }

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

  pcacheExitMutex();
}

**    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 1.9 2008/08/29 09:10:03 danielk1977 Exp $
*/

#ifndef _PCACHE_H_

typedef struct PgHdr PgHdr;
typedef struct PCache PCache;

  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_IN_STMTJRNL       0x002  /* Page is in the statement journal */
#define PGHDR_DIRTY             0x004  /* Page has changed */
#define PGHDR_NEED_SYNC         0x008  /* Peed to fsync this page */

#define PGHDR_NEED_READ         0x020  /* Content is unread */
#define PGHDR_IS_INIT           0x040  /* pData is initialized */
#define PGHDR_REUSE_UNLIKELY    0x080  /* Hint: Reuse is unlikely */
#define PGHDR_DONT_WRITE        0x100  /* Do not write content to disk */

/* Initialize and shutdown the page cache subsystem */
int sqlite3PcacheInitialize(void);
void sqlite3PcacheShutdown(void);

/* Page cache buffer management:
** These routines implement SQLITE_CONFIG_PAGECACHE.

/* 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*);

/* Set flags on all pages in the page cache */
void sqlite3PcacheSetFlags(PCache*, int andMask, int orMask);

/* Assert flags settings on all pages.  Debugging only */

void sqlite3PcacheAssertFlags(PCache*, int trueMask, int falseMask);




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

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