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AdministeringIn addition to administering the database server, you can tune performance, replicate data, and archive data.
System administrationThese topics contain concepts, procedures, and reference information for database and database server administrators to use for managing and tuning HCL OneDB™ database servers.
Performance GuideThe HCL OneDB™ Performance Guide describes how to configure and operate your HCL OneDB™ database server to improve overall system throughput and to improve the performance of SQL queries.
Improving individual query performanceYou can test, monitor, and improve queries.
Improve filter selectivityYou can control the amount of information that a query evaluates. The greater the precision with which you specify the desired rows, the greater the likelihood that your queries will complete quickly.
Avoid some filtersFor best performance, avoid filters for certain difficult regular expressions and filters for noninitial strings.
Avoid difficult regular expressionsThe MATCHES and LIKE keywords support wildcard matches, which are technically known as regular expressions. Some regular expressions are more difficult than others for the database server to process.

Avoid difficult regular expressions

The MATCHES and LIKE keywords support wildcard matches, which are technically known as regular expressions. Some regular expressions are more difficult than others for the database server to process.

A wildcard in the initial position, as in the following example (find customers whose first names do not end in y), forces the database server to examine every value in the column:

SELECT * FROM customer WHERE fname NOT LIKE '%y'

You cannot use an index with such a filter, so the table in this example must be accessed sequentially.

If a difficult test for a regular expression is essential, avoid combining it with a join. If necessary, process the single table and apply the test for a regular expression to select the desired rows. Save the result in a temporary table and join that table to the others.

Regular-expression tests with wildcards in the middle or at the end of the operand do not prevent the use of an index when one exists.