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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