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Overview
Comment:Make sure the wal-index mapping is always large enough to cover the entire active area of the wal-index.
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SHA1: 42705babba0e9d2ef078845854bebbd168f23366
User & Date: drh 2010-05-26 17:31:59
Context
2010-05-28
11:16
Add a test to walcksum.test to stress the checksum calculation. check-in: 778d0c17 user: dan tags: trunk
2010-05-26
17:31
Make sure the wal-index mapping is always large enough to cover the entire active area of the wal-index. check-in: 42705bab user: drh tags: trunk
15:06
Change the semantics of xShmGet() such that it will never increase the size of shared memory. xShmSize() must be used to grow the size of shared memory. A shared memory segment size cannot be shrunk (except by dropping it). check-in: 72de0073 user: drh tags: trunk
Changes
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Changes to src/wal.c.

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  **
  ** A dirty read of the wal-index header occurs if another thread or
  ** process happens to be writing to the wal-index header at roughly
  ** the same time as this thread is reading it. In this case it is 
  ** possible that an inconsistent header is read (which is detected
  ** using the header checksum mechanism).
  */
  if( walIndexTryHdr(pWal, pChanged)==0 ){
    return SQLITE_OK;
  }

  /* If the first attempt to read the header failed, lock the wal-index
  ** file with an exclusive lock and try again. If the header checksum 
  ** verification fails again, we can be sure that it is not simply a
  ** dirty read, but that the wal-index really does need to be 
  ** reconstructed by running log recovery.
  **
  ** In the paragraph above, an "exclusive lock" may be any of WRITE,
  ** PENDING, CHECKPOINT or RECOVER. If any of these are already held,
  ** no locking operations are required. If the caller currently holds
  ** a READ lock, then upgrade to a RECOVER lock before re-reading the
  ** wal-index header and revert to a READ lock before returning.
  */
  lockState = pWal->lockState;
  if( lockState>SQLITE_SHM_READ
   || SQLITE_OK==(rc = walSetLock(pWal, SQLITE_SHM_RECOVER)) 
  ){
    if( walIndexTryHdr(pWal, pChanged) ){
      *pChanged = 1;
      rc = walIndexRecover(pWal);
    }
    if( lockState==SQLITE_SHM_READ ){
      walSetLock(pWal, SQLITE_SHM_READ);









    }
  }

  return rc;
}

/*
................................................................................
  if( pWal->lockState==SQLITE_SHM_WRITE ){
    int unused;
    Pgno iMax = pWal->hdr.mxFrame;
    Pgno iFrame;
  
    assert( pWal->pWiData==0 );
    rc = walIndexReadHdr(pWal, &unused);



    if( rc==SQLITE_OK ){
      for(iFrame=pWal->hdr.mxFrame+1; rc==SQLITE_OK && iFrame<=iMax; iFrame++){
        assert( pWal->lockState==SQLITE_SHM_WRITE );
        rc = xUndo(pUndoCtx, pWal->pWiData[walIndexEntry(iFrame)]);
      }
      walCleanupHash(pWal);
    }







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  **
  ** A dirty read of the wal-index header occurs if another thread or
  ** process happens to be writing to the wal-index header at roughly
  ** the same time as this thread is reading it. In this case it is 
  ** possible that an inconsistent header is read (which is detected
  ** using the header checksum mechanism).
  */
  if( walIndexTryHdr(pWal, pChanged)!=0 ){



    /* If the first attempt to read the header failed, lock the wal-index
    ** file with an exclusive lock and try again. If the header checksum 
    ** verification fails again, we can be sure that it is not simply a
    ** dirty read, but that the wal-index really does need to be 
    ** reconstructed by running log recovery.
    **
    ** In the paragraph above, an "exclusive lock" may be any of WRITE,
    ** PENDING, CHECKPOINT or RECOVER. If any of these are already held,
    ** no locking operations are required. If the caller currently holds
    ** a READ lock, then upgrade to a RECOVER lock before re-reading the
    ** wal-index header and revert to a READ lock before returning.
    */
    lockState = pWal->lockState;
    if( lockState>SQLITE_SHM_READ
     || SQLITE_OK==(rc = walSetLock(pWal, SQLITE_SHM_RECOVER)) 
    ){
      if( walIndexTryHdr(pWal, pChanged) ){
        *pChanged = 1;
        rc = walIndexRecover(pWal);
      }
      if( lockState==SQLITE_SHM_READ ){
        walSetLock(pWal, SQLITE_SHM_READ);
      }
    }
  }

  /* Make sure the mapping is large enough to cover the entire wal-index */
  if( rc==SQLITE_OK ){
    int szWanted = walMappingSize(pWal->hdr.mxFrame);
    if( pWal->szWIndex<szWanted ){
      rc = walIndexMap(pWal, szWanted);
    }
  }

  return rc;
}

/*
................................................................................
  if( pWal->lockState==SQLITE_SHM_WRITE ){
    int unused;
    Pgno iMax = pWal->hdr.mxFrame;
    Pgno iFrame;
  
    assert( pWal->pWiData==0 );
    rc = walIndexReadHdr(pWal, &unused);
    if( rc==SQLITE_OK ){
      rc = walIndexMap(pWal, walMappingSize(iMax));
    }
    if( rc==SQLITE_OK ){
      for(iFrame=pWal->hdr.mxFrame+1; rc==SQLITE_OK && iFrame<=iMax; iFrame++){
        assert( pWal->lockState==SQLITE_SHM_WRITE );
        rc = xUndo(pUndoCtx, pWal->pWiData[walIndexEntry(iFrame)]);
      }
      walCleanupHash(pWal);
    }