Because reading and writing data to disk is a relatively slow operation, disk I/O is a common database performance bottleneck. The database engine performs three primary types of I/O operations:

  • Database I/O
  • Before-image I/O
  • After-image I/O (relevant only if after-imaging is enabled)

If performance monitoring indicates that I/O resources are overloaded, try the techniques in the following sections to better balance disk I/O.

The best way to reduce disk I/O bottlenecks is to spread I/O across several physical disks, allowing multiple disk accesses to occur concurrently. You can extend files across many disk volumes or file systems.