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Message Posted: Wed, 21 Mar 2001 @ 09:16:29 GMT


     
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Subj:   Re: Placement of VARCHAR and COMPRESSed Columns In A Row
 
From:   Dave Sedgwick

David,

We have compress on many of our fact columns, for example on 40 columns of our 56 column main order table. This came out of experiments for performance on a very large but sparsley populated main fact table used for a Business Objects development. Whilst there is a minor overhead to populate the table, we found a big improvement in space saving and also in query performance. I understand that this is because more data is brought into each (64k?) read block as the compressed values are much smaller. This only works if you have a value that is very common in the column in question. In our case as it is a sparsley populated dimension table where zero is very common.

Dave



     
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