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Overview
Comment:Merge change to drop the mutex on the multiplexor before entering the xRead VFS call, in order to enhance parallelizability.
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SHA1:3c566e41e4c9c66960cc5a3ddee8556835237999
User & Date: drh 2013-11-08 12:14:50
Context
2013-11-08
15:19
Performance improvements: Avoid unnecessary seeks when doing a single-row UPDATE on a WITHOUT ROWID table. check-in: 6f187a0f user: drh tags: trunk
12:14
Merge change to drop the mutex on the multiplexor before entering the xRead VFS call, in order to enhance parallelizability. check-in: 3c566e41 user: drh tags: trunk
01:09
Optimize out a NotExists/NotFound opcode that occurs in UPDATE processing after constraint checks if there is no possiblity that the constraint checking code might have moved the cursor. check-in: 74e3ee2e user: drh tags: trunk
2013-10-21
13:15
Drop the mutex on the multiplexor before entering the xRead VFS call. Closed-Leaf check-in: a00d2ed4 user: drh tags: multiplex-parallel-read
Changes
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Changes to src/test_multiplex.c.

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  void *pBuf,
  int iAmt,
  sqlite3_int64 iOfst
){
  multiplexConn *p = (multiplexConn*)pConn;
  multiplexGroup *pGroup = p->pGroup;
  int rc = SQLITE_OK;

  multiplexEnter();
  if( !pGroup->bEnabled ){
    sqlite3_file *pSubOpen = multiplexSubOpen(pGroup, 0, &rc, NULL, 0);

    if( pSubOpen==0 ){
      rc = SQLITE_IOERR_READ;
    }else{
      rc = pSubOpen->pMethods->xRead(pSubOpen, pBuf, iAmt, iOfst);
    }
  }else{
    while( iAmt > 0 ){
      int i = (int)(iOfst / pGroup->szChunk);

      sqlite3_file *pSubOpen = multiplexSubOpen(pGroup, i, &rc, NULL, 1);

      if( pSubOpen ){
        int extra = ((int)(iOfst % pGroup->szChunk) + iAmt) - pGroup->szChunk;
        if( extra<0 ) extra = 0;
        iAmt -= extra;
        rc = pSubOpen->pMethods->xRead(pSubOpen, pBuf, iAmt,
                                       iOfst % pGroup->szChunk);
        if( rc!=SQLITE_OK ) break;
................................................................................
        iAmt = extra;
      }else{
        rc = SQLITE_IOERR_READ;
        break;
      }
    }
  }

  multiplexLeave();
  return rc;
}

/* Pass xWrite requests thru to the original VFS after
** determining the correct chunk to operate on.
** Break up writes across chunk boundaries.
*/







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  void *pBuf,
  int iAmt,
  sqlite3_int64 iOfst
){
  multiplexConn *p = (multiplexConn*)pConn;
  multiplexGroup *pGroup = p->pGroup;
  int rc = SQLITE_OK;
  int nMutex = 0;
  multiplexEnter(); nMutex++;
  if( !pGroup->bEnabled ){
    sqlite3_file *pSubOpen = multiplexSubOpen(pGroup, 0, &rc, NULL, 0);
    multiplexLeave(); nMutex--;
    if( pSubOpen==0 ){
      rc = SQLITE_IOERR_READ;
    }else{
      rc = pSubOpen->pMethods->xRead(pSubOpen, pBuf, iAmt, iOfst);
    }
  }else{
    while( iAmt > 0 ){
      int i = (int)(iOfst / pGroup->szChunk);
      if( nMutex==0 ){ multiplexEnter(); nMutex++; }
      sqlite3_file *pSubOpen = multiplexSubOpen(pGroup, i, &rc, NULL, 1);
      multiplexLeave(); nMutex--;
      if( pSubOpen ){
        int extra = ((int)(iOfst % pGroup->szChunk) + iAmt) - pGroup->szChunk;
        if( extra<0 ) extra = 0;
        iAmt -= extra;
        rc = pSubOpen->pMethods->xRead(pSubOpen, pBuf, iAmt,
                                       iOfst % pGroup->szChunk);
        if( rc!=SQLITE_OK ) break;
................................................................................
        iAmt = extra;
      }else{
        rc = SQLITE_IOERR_READ;
        break;
      }
    }
  }
  assert( nMutex==0 || nMutex==1 );
  if( nMutex ) multiplexLeave();
  return rc;
}

/* Pass xWrite requests thru to the original VFS after
** determining the correct chunk to operate on.
** Break up writes across chunk boundaries.
*/