Optimizing restore performance

When you perform a restore operation, Db2® database products will automatically choose an optimal value for the number of buffers, the buffersize and the parallelism settings. The values will be based on the amount of utility heap memory available, the number of processors available and the database configuration.

Therefore, depending on the amount of storage available on your system, you should consider allocating more memory by increasing the util_heap_sz configuration parameter. The objective is to minimize the time it takes to complete a restore operation. Unless you explicitly enter a value for the following RESTORE DATABASE command parameters, Db2 database products will select one for them:
  • WITH num-buffers BUFFERS
  • PARALLELISM n
  • BUFFER buffer-size
For restore operations, a multiple of the buffer size used by the backup operation will always be used. You can specify a buffer size when you issue the RESTORE DATABASE command but you need to make sure that it is a multiple of the backup buffer size.

You can also choose to do any of the following to reduce the amount of time required to complete a restore operation:

  • Increase the restore buffer size.

    The restore buffer size must be a positive integer multiple of the backup buffer size specified during the backup operation. If an incorrect buffer size is specified, the buffers allocated will be the smallest acceptable size.

  • Increase the number of buffers.

    The value you specify must be a multiple of the buffersize that was used for the backup, otherwise it will be rounded down to the closest multiple of the backup buffersize.

  • Increase the value of the PARALLELISM parameter.

    This will increase the number of buffer manipulators (BM) that will be used to write to the database during the restore operation.

  • Increase the utility heap size

    This will increase the memory that can be used simultaneously by the other utilities.