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Message Posted: Fri, 24 Feb 2006 @ 18:30:54 GMT

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Alan-

Here is a knowledge article on the subject:

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Question: Is it necessary to recollect statistics after using the 'reconfig' utility?

Answer: No because...

The 'config' and 'reconfig' utilities are used to define access module processor (AMPs) and parsing engines (PEs) that will operate together as the Teradata database. The 'reconfig' utility is the second step of the process and typically is used to implement a change in the number of AMPs that was defined during 'config'.

Statistics generate information about the number and distribution of values in a table column, or in one or more columns that are defined as an index, and generally do not need to be altered unless one of the following conditions exist:

- A table has been extensively modified (more than 10% of the rows added or deleted) since statistics were last collected.

- Performance does not seem to be improved by the statistics collected.

- The statistics are not useful for the requests currently being entered.

- The table is not currently being used.

The reconfig utility is typically used to alter the number of AMPs in a DBS; during reconfiguration, data is simply redistributed among those AMPs. Because a reconfig operation doesn't change the data itself (it just moves it around), there is no need to collect statistics after a reconfig. Remember, however, that if NUSIs are dropped as part of the reconfig, statistics will need to be recollected on them once they are recreated.

Additional Information/Comments:

For additional information on 'reconfig' refer to Chapter 10 of the 'Teradata(r) DBS for UNIX(r) Utilities Reference Manual'. For additional information on statistics refer to Chapter 17 of the 'Teradata(r) DBS for UNIX(r) Database Design and Administration Manual'.

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Having said that, we should make a couple of points.... Your statistics should be kept up to date. The optimizer takes into consideration the hardware configuration so I would expect plans to change. Because of this you should capture "before image" explains for a sample of your queries and any critical SQL. I would also suggest that you save a copy of your ResUsage history. If you don't have a benchmark, now would be the time to establish one. Finally, be sure to increase your spool ceilings to reflect the increased number of AMPS.

Hope this helps.

-dave.clark

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