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Overview
Comment:Clarification of the pagerFlushOnCommit() logic.
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SHA1: 3401d9dcdbec390564574e8d2972c944c204e025
User & Date: drh 2016-05-13 12:12:38
Context
2016-05-13
15:22
Remove the unused PGHDR_NEED_READ flag. Add invariant checking (during SQLITE_DEBUG builds only) for the PgHdr object. check-in: 771c5411 user: drh tags: trunk
12:12
Clarification of the pagerFlushOnCommit() logic. check-in: 3401d9dc user: drh tags: trunk
11:50
Fix pager_end_transaction() to ensure that a ROLLBACK does not clobber unwritten pages in a TEMP file pcache. check-in: 9495d338 user: drh tags: trunk
Changes
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Changes to src/pager.c.

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  }
  return rc;
}

static int pager_truncate(Pager *pPager, Pgno nPage);

/*
** The write transaction open on the pager passed as the only argument is
** being committed. This function returns true if all dirty pages should

** be flushed to disk, or false otherwise. Pages should be flushed to disk
** unless one of the following is true:
**
**   * The db is an in-memory database.
**
**   * The db is a temporary database and the db file has not been opened.

**
**   * The db is a temporary database and the cache contains less than
**     C/4 dirty pages, where C is the configured cache-size.



*/
static int pagerFlushOnCommit(Pager *pPager){
  if( pPager->tempFile==0 ) return 1;

  if( !isOpen(pPager->fd) ) return 0;
  return (sqlite3PCachePercentDirty(pPager->pPCache)>=25);
}

/*
** This routine ends a transaction. A transaction is usually ended by 
** either a COMMIT or a ROLLBACK operation. This routine may be called 
................................................................................
  }
#endif

  sqlite3BitvecDestroy(pPager->pInJournal);
  pPager->pInJournal = 0;
  pPager->nRec = 0;
  if( rc==SQLITE_OK ){
    if( !pPager->tempFile || (bCommit && pagerFlushOnCommit(pPager)) ){
      sqlite3PcacheCleanAll(pPager->pPCache);
    }else{
      sqlite3PcacheClearWritable(pPager->pPCache);
    }
    sqlite3PcacheTruncate(pPager->pPCache, pPager->dbSize);
  }

................................................................................
      pPager->zFilename, zMaster, pPager->dbSize));

  /* If no database changes have been made, return early. */
  if( pPager->eState<PAGER_WRITER_CACHEMOD ) return SQLITE_OK;

  assert( MEMDB==0 || pPager->tempFile );
  assert( isOpen(pPager->fd) || pPager->tempFile );
  if( 0==pagerFlushOnCommit(pPager) ){
    /* If this is an in-memory db, or no pages have been written to, or this
    ** function has already been called, it is mostly a no-op.  However, any
    ** backup in progress needs to be restarted.  */
    sqlite3BackupRestart(pPager->pBackup);
  }else{
    if( pagerUseWal(pPager) ){
      PgHdr *pList = sqlite3PcacheDirtyList(pPager->pPCache);







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  }
  return rc;
}

static int pager_truncate(Pager *pPager, Pgno nPage);

/*
** The write transaction open on pPager is being committed (bCommit==1)
** or rolled back (bCommit==0).
**
** Return TRUE if and only if all dirty pages should be flushed to disk.

**
** Rules:
**
**   *  For non-TEMP databases, always sync to disk.  This is necessary
**      for transactions to be durable.
**

**   *  Sync TEMP database only on a COMMIT (not a ROLLBACK) when the backing
**      file has been created already (via a spill on pagerStress()) and
**      when the number of dirty pages in memory exceeds 25% of the total
**      cache size.
*/
static int pagerFlushOnCommit(Pager *pPager, int bCommit){
  if( pPager->tempFile==0 ) return 1;
  if( !bCommit ) return 0;
  if( !isOpen(pPager->fd) ) return 0;
  return (sqlite3PCachePercentDirty(pPager->pPCache)>=25);
}

/*
** This routine ends a transaction. A transaction is usually ended by 
** either a COMMIT or a ROLLBACK operation. This routine may be called 
................................................................................
  }
#endif

  sqlite3BitvecDestroy(pPager->pInJournal);
  pPager->pInJournal = 0;
  pPager->nRec = 0;
  if( rc==SQLITE_OK ){
    if( pagerFlushOnCommit(pPager, bCommit) ){
      sqlite3PcacheCleanAll(pPager->pPCache);
    }else{
      sqlite3PcacheClearWritable(pPager->pPCache);
    }
    sqlite3PcacheTruncate(pPager->pPCache, pPager->dbSize);
  }

................................................................................
      pPager->zFilename, zMaster, pPager->dbSize));

  /* If no database changes have been made, return early. */
  if( pPager->eState<PAGER_WRITER_CACHEMOD ) return SQLITE_OK;

  assert( MEMDB==0 || pPager->tempFile );
  assert( isOpen(pPager->fd) || pPager->tempFile );
  if( 0==pagerFlushOnCommit(pPager, 1) ){
    /* If this is an in-memory db, or no pages have been written to, or this
    ** function has already been called, it is mostly a no-op.  However, any
    ** backup in progress needs to be restarted.  */
    sqlite3BackupRestart(pPager->pBackup);
  }else{
    if( pagerUseWal(pPager) ){
      PgHdr *pList = sqlite3PcacheDirtyList(pPager->pPCache);