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Breck Carter
Last modified: February 12, 1998
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Tip 77: Sybase SQL Anywhere
Performance Tips & Techniques

35 - Put Different Data On Different Drives

With databases the saying "Two heads are better than one" translates into this Rule of Thumb: "Put different data in different files on different drives." If your application rapidly switches back and forth between different tables, indexes and files then its speed will by limited by the disk drive's ability to move its read/write head from one location to another. Placing different data on different drives gets more heads working for you and reduces the frequency of movement for any particular head.

Here are some things you can try:

The DBLOG utility can be used to change the location of the log file associated with the database. If you start switching between different log files you might have to delete old versions before starting the server.

When it comes to breaking the database up into separate files the CREATE DBSPACE <dbspace-name> AS <file-name> statement sets up the files and then CREATE TABLE and CREATE INDEX ... IN <dbspace-name> specify which file to use for which table and index.

The difference can be dramatic. In one test where the transaction log was moved from the same fast drive to a slower drive on a slower computer on the other side of a slow LAN, an update process dropped from 13 seconds to five seconds. In other words two heads really are better than one even if one of the heads is much slower.

Be sure to use different physical drives rather than different partitions of the same drive; e.g., make sure C: and D: don't share the same head.

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