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Message Posted: Fri, 10 Jun 2005 @ 18:15:10 GMT

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Christian,

There is nothing in the statistics themselves having to do with the number of AMPs in your configuration. Neither are pre-upgrade statistics ignored. They are used.

The recommendation to collect stats after a reconfig is to make sure that at that point you have everything as clean and up-to-date as possible, so that your system is in a position of greatest performance potential.

Because not all sites collect stats as often as they should, making recollecting stats a recommendation when upgrading is a way to eliminate stale statistics as a contributer to post-upgrade performance anomalies. You could just as easily do the statistics collection just prior to the reconfig, with the same result (although it would take longer to do so,with fewer nodes).

Even though stats do not carry information reflecting the increased number of AMPs, you could get different plans, worse plans, after an upgrade solely because your statistics are stale. This is because the cost formulas used by the optimizer do take into consideration the # of AMPs. With the cost formulas changed, state stats which might not have been causing a problem in the old configuration, could contribute to worse plans in the new one.

You did not say when you had last collected stats prior to the upgrade. Could it be they were a bit outdated?

Thanks, -Carrie

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