The BI file is organized into clusters on disk. As the database engine writes data to the BI file, these clusters fill up. When a cluster fills, the engine must ensure that all modified database buffer blocks referenced by notes in that cluster are written to disk. This is known as a checkpoint. Checkpointing reduces recovery time and lets the engine reuse BI disk space. Raising the BI cluster size increases the interval between checkpoints.

Raising the BI cluster size can reduce the I/O overhead of writing modified database buffers to disk. It also lets you defer writes and collect more changes before writing a block; this lets you write multiple changes with the same write.

Larger cluster sizes generally increase performance. However, they also have significant drawbacks:

  • Increased disk space usage for the BI file
  • Longer crash recovery periods
  • Longer checkpoint times (run APWs to eliminate this drawback)

To change the cluster size:

  1. Use the PROSHUT command or the PROMON Shutdown a Database option to shut down the database.
  2. Enter the following command:proutil db-name -C truncate bi -bi size

    For size, specify the new cluster size in kilobytes. The number must be a multiple of 16 in the range 16 to 262128 (16K-256MB). The default cluster size is 512K. Cluster sizes from 512 to 16384 are common.

    You can also change the BI block size with this command. You might want to do so at this time. For more information, see Increase the BI block size.