Database Optimization: Measuring Oracle disk I/O speed

Monday Mar 1st 2004 by Staff

An effective Oracle database optimization plan requires the measurement of physical disk access and an assessment of relative costs. This article shows how valuable processing information for this assessment can be gleaned from the standard Oracle STATSPACK report.


Because all Oracle databases retrieve and store data, the relative cost of physical disk access is an important topic. In Oracle, we see two types of data block access:

  • db file sequential read-A single-block read (i.e., index fetch by ROWID)
  • db file scattered read-A multiblock read (a full-table scan, OPQ, sorting)

Physical disk speed is an important factor in weighing these costs. Faster disk access speeds can reduce the costs of a full-table scan vs. single block reads to a negligible level.

For example, the new solid state disks provide up to 100,000 I/Os per second, six times faster than traditional disk devices. In a solid-state disk environment, disk I/O is much faster and multiblock reads become far cheaper than with traditional disks.

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