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Message Posted: Tue, 03 Aug 2004 @ 15:57:39 GMT

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Subj:   Re: Sampling of Pages
From:   Victor Sokovin


  is there any way to have teradata sample a table by pages rather than rows ? I know that the data obtained that way is not quite representative due to clustering issues, but I am basically after reduction of I/Os.  

I am not sure I understand what you mean by pages in this context but I'll try to say a few words about how SAMPLE works in TD.

As of V2R5 there are two types of samples: proportional (default) and randomized. On earlier releases we only had the randomized version so there were no real choices there.

Proportional sampling is faster as it assumes data is stratified across AMPs and does not attempt to consider all possible samples across all AMPs (the quality of sampling is lower of course in this case but you indicated that that was not a problem). That reduces I/O, which you were after.



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