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Message Posted: Thu, 05 Nov 2009 @ 15:30:43 GMT

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Good morning.

Collecting all statistics recommended by Diagnostic Helpstats is definitely NOT by the book. You really have to be careful with these recommendations and should think of them as suggestions to test and validate only.

Here are some things to keep in mind, documented by the Teradata Professional Services Performance and Workload Management COE:

Diagnostic Helpstats can be very helpful, but use caution.

It will not give any indication whatsoever of stale stats. If stats exist, the optimizer trusts and uses them.

Carefully choose stats recommended by Diagnostic Helpstats. Collecting too many statistics can dramatically impact batch data collection cycles and render the stats unmaintainable.

Consider collecting on single column and index recommendations first.

Consider collecting on any recommendations made by the optimizer, including multi-column, for very small tables that take only seconds to collect.

Validate that your new collected stats improve the query plan. If they do not, drop them.

If necessary, consider some of the multi-column statistics recommendations being very careful to test to ensure that they provide benefit and are worth the collection time. If not, drop them.

Steve Woodrow

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