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Archives of the TeradataForum
Message Posted: Thu, 03 Aug 2006 @ 12:34:11 GMT
| Subj: | | Re: Recommendations from Statistics Wizard |
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| From: | | Victor Sokovin |
| | Can anyone explain how the using sample in collect statistics works, I was expecting a sample to return less unique values than a full
table scan. | |
That is true but based on that sample TD has to make an estimate (extrapolation) for the entire table and that estimate may be rather
inaccurate. You might want to check with your DBA the database settings for the sample based statistics. The number of AMPs from which samples are
taken can be increased, and that should improve the quality of the estimates. If you use a small number of AMPs and the data is skewed you might
get pretty bad estimates, especially for small tables.
However, I am not sure it is worth going into all these troubles for small tables for which you can easily opt for full stats and safely ignore
recommendations of the Wizard.
Regards,
Victor
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