Unexpectedly long loads or queries

Possible causes

Action

Monitor paging to determine if thrashing is a problem.

Reset your buffer sizes as needed. See the section “Monitoring the buffer caches” in Chapter 6, “Monitoring and Tuning Performance” of the Sybase IQ Performance and Tuning Guide.

If you monitor paging and determine that thrashing is a problem, you can also limit the amount of thrashing during the execution of a statement which includes a query that involves hash algorithms. Adjusting the HASH_THRASHING_PERCENT database option controls the percentage of hard disk I/Os allowed before the statement is rolled back and an error is returned.

The default value of HASH_THRASHING_PERCENT is 10%. Increasing HASH_THRASHING_PERCENT permits more paging to disk before a rollback and decreasing HASH_THRASHING_PERCENT permits less paging before a rollback.

Queries involving hash algorithms that executed in earlier versions of Sybase IQ may now be rolled back when the default HASH_THRASHING_PERCENT limit is reached. The error "Hash insert thrashing detected." or "Hash find thrashing detected." (SQLState QFA43, SQLCode -1001047) is reported. Take one or more of the following actions to provide the query with the resources required for execution:

To identify possible problems with a query, generate a query plan by running the query with the temporary database options QUERY_PLAN = 'ON' and QUERY _DETAIL = 'ON', then examine the estimates in the query plan. The option QUERY_PLAN_AFTER_RUN = 'ON' provides additional information, as the query plan is printed after the query has finished running. The generated query plan is in the message log file.

See also