pager.c

来自「SQLite 2.8.6 源代码,用来在Linux/Unix/Windows上编」· C语言 代码 · 共 2,008 行 · 第 1/5 页

  int rc = SQLITE_OK;
  assert( pPg->nRef>0 );
  assert( pPager->state!=SQLITE_UNLOCK );
  if( pPager->state==SQLITE_READLOCK ){
    assert( pPager->aInJournal==0 );
    rc = sqliteOsWriteLock(&pPager->fd);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    pPager->state = SQLITE_WRITELOCK;
    pPager->dirtyFile = 0;
    TRACE1("TRANSACTION\n");
    if( pPager->useJournal && !pPager->tempFile ){
      rc = pager_open_journal(pPager);
    }
  }
  return rc;
}

/*
** Mark a data page as writeable.  The page is written into the journal 
** if it is not there already.  This routine must be called before making
** changes to a page.
**
** The first time this routine is called, the pager creates a new
** journal and acquires a write lock on the database.  If the write
** lock could not be acquired, this routine returns SQLITE_BUSY.  The
** calling routine must check for that return value and be careful not to
** change any page data until this routine returns SQLITE_OK.
**
** If the journal file could not be written because the disk is full,
** then this routine returns SQLITE_FULL and does an immediate rollback.
** All subsequent write attempts also return SQLITE_FULL until there
** is a call to sqlitepager_commit() or sqlitepager_rollback() to
** reset.
*/
int sqlitepager_write(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;

  /* Check for errors
  */
  if( pPager->errMask ){ 
    return pager_errcode(pPager);
  }
  if( pPager->readOnly ){
    return SQLITE_PERM;
  }

  /* Mark the page as dirty.  If the page has already been written
  ** to the journal then we can return right away.
  */
  pPg->dirty = 1;
  if( pPg->inJournal && (pPg->inCkpt || pPager->ckptInUse==0) ){
    pPager->dirtyFile = 1;
    return SQLITE_OK;
  }

  /* If we get this far, it means that the page needs to be
  ** written to the transaction journal or the ckeckpoint journal
  ** or both.
  **
  ** First check to see that the transaction journal exists and
  ** create it if it does not.
  */
  assert( pPager->state!=SQLITE_UNLOCK );
  rc = sqlitepager_begin(pData);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  assert( pPager->state==SQLITE_WRITELOCK );
  if( !pPager->journalOpen && pPager->useJournal ){
    rc = pager_open_journal(pPager);
    if( rc!=SQLITE_OK ) return rc;
  }
  assert( pPager->journalOpen || !pPager->useJournal );
  pPager->dirtyFile = 1;

  /* The transaction journal now exists and we have a write lock on the
  ** main database file.  Write the current page to the transaction 
  ** journal if it is not there already.
  */
  if( !pPg->inJournal && pPager->useJournal ){
    if( (int)pPg->pgno <= pPager->origDbSize ){
      int szPg;
      u32 saved;
      if( journal_format>=JOURNAL_FORMAT_3 ){
        u32 cksum = pager_cksum(pPager, pPg->pgno, pData);
        saved = *(u32*)PGHDR_TO_EXTRA(pPg);
        store32bits(cksum, pPg, SQLITE_PAGE_SIZE);
        szPg = SQLITE_PAGE_SIZE+8;
      }else{
        szPg = SQLITE_PAGE_SIZE+4;
      }
      store32bits(pPg->pgno, pPg, -4);
      rc = sqliteOsWrite(&pPager->jfd, &((char*)pData)[-4], szPg);
      if( journal_format>=JOURNAL_FORMAT_3 ){
        *(u32*)PGHDR_TO_EXTRA(pPg) = saved;
      }
      if( rc!=SQLITE_OK ){
        sqlitepager_rollback(pPager);
        pPager->errMask |= PAGER_ERR_FULL;
        return rc;
      }
      pPager->nRec++;
      assert( pPager->aInJournal!=0 );
      pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
      pPg->needSync = !pPager->noSync;
      pPg->inJournal = 1;
      if( pPager->ckptInUse ){
        pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
        page_add_to_ckpt_list(pPg);
      }
      TRACE3("JOURNAL %d %d\n", pPg->pgno, pPg->needSync);
    }else{
      pPg->needSync = !pPager->journalStarted && !pPager->noSync;
      TRACE3("APPEND %d %d\n", pPg->pgno, pPg->needSync);
    }
    if( pPg->needSync ){
      pPager->needSync = 1;
    }
  }

  /* If the checkpoint journal is open and the page is not in it,
  ** then write the current page to the checkpoint journal.  Note that
  ** the checkpoint journal always uses the simplier format 2 that lacks
  ** checksums.  The header is also omitted from the checkpoint journal.
  */
  if( pPager->ckptInUse && !pPg->inCkpt && (int)pPg->pgno<=pPager->ckptSize ){
    assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
    store32bits(pPg->pgno, pPg, -4);
    rc = sqliteOsWrite(&pPager->cpfd, &((char*)pData)[-4], SQLITE_PAGE_SIZE+4);
    if( rc!=SQLITE_OK ){
      sqlitepager_rollback(pPager);
      pPager->errMask |= PAGER_ERR_FULL;
      return rc;
    }
    pPager->ckptNRec++;
    assert( pPager->aInCkpt!=0 );
    pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    page_add_to_ckpt_list(pPg);
  }

  /* Update the database size and return.
  */
  if( pPager->dbSize<(int)pPg->pgno ){
    pPager->dbSize = pPg->pgno;
  }
  return rc;
}

/*
** Return TRUE if the page given in the argument was previously passed
** to sqlitepager_write().  In other words, return TRUE if it is ok
** to change the content of the page.
*/
int sqlitepager_iswriteable(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  return pPg->dirty;
}

/*
** Replace the content of a single page with the information in the third
** argument.
*/
int sqlitepager_overwrite(Pager *pPager, Pgno pgno, void *pData){
  void *pPage;
  int rc;

  rc = sqlitepager_get(pPager, pgno, &pPage);
  if( rc==SQLITE_OK ){
    rc = sqlitepager_write(pPage);
    if( rc==SQLITE_OK ){
      memcpy(pPage, pData, SQLITE_PAGE_SIZE);
    }
    sqlitepager_unref(pPage);
  }
  return rc;
}

/*
** A call to this routine tells the pager that it is not necessary to
** write the information on page "pgno" back to the disk, even though
** that page might be marked as dirty.
**
** The overlying software layer calls this routine when all of the data
** on the given page is unused.  The pager marks the page as clean so
** that it does not get written to disk.
**
** Tests show that this optimization, together with the
** sqlitepager_dont_rollback() below, more than double the speed
** of large INSERT operations and quadruple the speed of large DELETEs.
**
** When this routine is called, set the alwaysRollback flag to true.
** Subsequent calls to sqlitepager_dont_rollback() for the same page
** will thereafter be ignored.  This is necessary to avoid a problem
** where a page with data is added to the freelist during one part of
** a transaction then removed from the freelist during a later part
** of the same transaction and reused for some other purpose.  When it
** is first added to the freelist, this routine is called.  When reused,
** the dont_rollback() routine is called.  But because the page contains
** critical data, we still need to be sure it gets rolled back in spite
** of the dont_rollback() call.
*/
void sqlitepager_dont_write(Pager *pPager, Pgno pgno){
  PgHdr *pPg;

  pPg = pager_lookup(pPager, pgno);
  pPg->alwaysRollback = 1;
  if( pPg && pPg->dirty ){
    if( pPager->dbSize==(int)pPg->pgno && pPager->origDbSize<pPager->dbSize ){
      /* If this pages is the last page in the file and the file has grown
      ** during the current transaction, then do NOT mark the page as clean.
      ** When the database file grows, we must make sure that the last page
      ** gets written at least once so that the disk file will be the correct
      ** size. If you do not write this page and the size of the file
      ** on the disk ends up being too small, that can lead to database
      ** corruption during the next transaction.
      */
    }else{
      TRACE2("DONT_WRITE %d\n", pgno);
      pPg->dirty = 0;
    }
  }
}

/*
** A call to this routine tells the pager that if a rollback occurs,
** it is not necessary to restore the data on the given page.  This
** means that the pager does not have to record the given page in the
** rollback journal.
*/
void sqlitepager_dont_rollback(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;

  if( pPager->state!=SQLITE_WRITELOCK || pPager->journalOpen==0 ) return;
  if( pPg->alwaysRollback || pPager->alwaysRollback ) return;
  if( !pPg->inJournal && (int)pPg->pgno <= pPager->origDbSize ){
    assert( pPager->aInJournal!=0 );
    pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    pPg->inJournal = 1;
    if( pPager->ckptInUse ){
      pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
      page_add_to_ckpt_list(pPg);
    }
    TRACE2("DONT_ROLLBACK %d\n", pPg->pgno);
  }
  if( pPager->ckptInUse && !pPg->inCkpt && (int)pPg->pgno<=pPager->ckptSize ){
    assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
    assert( pPager->aInCkpt!=0 );
    pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    page_add_to_ckpt_list(pPg);
  }
}

/*
** Commit all changes to the database and release the write lock.
**
** If the commit fails for any reason, a rollback attempt is made
** and an error code is returned.  If the commit worked, SQLITE_OK
** is returned.
*/
int sqlitepager_commit(Pager *pPager){
  int rc;
  PgHdr *pPg;

  if( pPager->errMask==PAGER_ERR_FULL ){
    rc = sqlitepager_rollback(pPager);
    if( rc==SQLITE_OK ){
      rc = SQLITE_FULL;
    }
    return rc;
  }
  if( pPager->errMask!=0 ){
    rc = pager_errcode(pPager);
    return rc;
  }
  if( pPager->state!=SQLITE_WRITELOCK ){
    return SQLITE_ERROR;
  }
  TRACE1("COMMIT\n");
  if( pPager->dirtyFile==0 ){
    /* Exit early (without doing the time-consuming sqliteOsSync() calls)
    ** if there have been no changes to the database file. */
    assert( pPager->needSync==0 );
    rc = pager_unwritelock(pPager);
    pPager->dbSize = -1;
    return rc;
  }
  assert( pPager->journalOpen );
  if( pPager->needSync && sqliteOsSync(&pPager->jfd)!=SQLITE_OK ){
    goto commit_abort;
  }
  pPg = pager_get_all_dirty_pages(pPager);
  if( pPg ){
    rc = pager_write_pagelist(pPg);
    if( rc || (!pPager->noSync && sqliteOsSync(&pPager->fd)!=SQLITE_OK) ){
      goto commit_abort;
    }
  }
  rc = pager_unwritelock(pPager);
  pPager->dbSize = -1;
  return rc;

  /* Jump here if anything goes wrong during the commit process.
  */
commit_abort:
  rc = sqlitepager_rollback(pPager);
  if( rc==SQLITE_OK ){
    rc = SQLITE_FULL;
  }
  return rc;
}

/*
** Rollback all changes.  The database falls back to read-only mode.
** All in-memory cache pages revert to their original data contents.
** The journal is deleted.
**
** This routine cannot fail unless some other process is not following
** the correct locking protocol (SQLITE_PROTOCOL) or unless some other
** process is writing trash into the journal file (SQLITE_CORRUPT) or
** unless a prior malloc() failed (SQLITE_NOMEM).  Appropriate error
** codes are returned for all these occasions.  Otherwise,
** SQLITE_OK is returned.
*/
int sqlitepager_rollback(Pager *pPager){
  int rc;
  TRACE1("ROLLBACK\n");
  if( !pPager->dirtyFile || !pPager->journalOpen ){
    rc = pager_unwritelock(pPager);
    pPager->dbSize = -1;
    return rc;
  }

  if( pPager->errMask!=0 && pPager->errMask!=PAGER_ERR_FULL ){
    if( pPager->state>=SQLITE_WRITELOCK ){
      pager_playback(pPager, 1);
    }
    return pager_errcode(pPager);
  }
  if( pPager->state!=SQLITE_WRITELOCK ){
    return SQLITE_OK;
  }
  rc = pager_playback(pPager, 1);
  if( rc!=SQLITE_OK ){
    rc = SQLITE_CORRUPT;
    pPager->errMask |= PAGER_ERR_CORRUPT;
  }
  pPager->dbSize = -1;
  return rc;
}

/*
** Return TRUE if the database file is opened read-only.  Return FALSE
** if the database is (in theory) writable.
*/
int sqlitepager_isreadonly(Pager *pPager){
  return pPager->readOnly;
}

/*
** This routine is used for testing and analysis only.
*/
int *sqlitepager_stats(Pager *pPager){
  static int a[9];
  a[0] = pPager->nRef;
  a[1] = pPager->nPage;
  a[2] = pPager->mxPage;
  a[3] = pPager->dbSize;
  a[4] = pPager->state;
  a[5] = pPager->errMask;
  a[6] = pPager->nHit;
  a[7] = pPager->nMiss;
  a[8] = pPager->nOvfl;
  return a;
}

/*
** Set the checkpoint.
**
** This routine should be called with the transaction journal already
** open.  A new checkpoint journal is created that can be used to rollback
** changes of a single SQL command within a larger transaction.
*/
int sqlitepager_ckpt_begin(Pager *pPager){
  int rc;
  char zTemp[SQLITE_TEMPNAME_SIZE];
  if( !pPager->journalOpen ){
    pPager->ckptAutoopen = 1;
    return SQLITE_OK;
  }
  assert( pPager->journalOpen );
  assert( !pPager->ckptInUse );
  pPager->aInCkpt = sqliteMalloc( pPager->dbSize/8 + 1 );
  if( pPager->aInCkpt==0 ){
    sqliteOsReadLock(&pPager->fd);
    return