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Message Posted: Fri, 07 May 2004 @ 10:47:42 GMT


     
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Subj:   Re: Statistic collection questions
 
From:   Martin O Brien

Hi ,

If you can afford it stats should be collected on joining columns and columns that you use for limiting resultset ( columns in the where clause). Of these columns it is more important to collect stats on columns which are heavily skewed towards a few values (as Teradata will use default stats for these columns if no actual stats on the columns and stats are on any other column in table).

The frequency depends on how frequently the table changes ( insert/update /deletes ). I've heard that once the table changes by about 10 % you should recollect stats. ( Thats our rule of thumb for what its worth ).

Be wary of date columns which are indices, we collect stats on these columns much more frequently (nightly if possible ). We have found that Teradata sometimes doesn't use the index when it should if this is not done.


Cheers,

Martin



     
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