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Message Posted: Fri, 18 Aug 2006 @ 11:39:55 GMT

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David,

In most circumstances the response time for the tactical queries is going to be more important than the DS scan performance. This is particularly true if options such as PPI or other indexing strategies (including sparse join index) are being utilized to reduce the need to scan the entire table. Assuming that you care more about the tactical response time (which I believe you should), then a good compromise block size for a table being accessed strategically and tactically is 64KB. 64KB blocks seem to be a common solution for others that have grappled with finding this common ground.

Another consideration, however, is whether or not you are using full cylinder read. If DS queries are able to take advantage of FCR then the I/O demand involved in scanning a table can be greatly reduced. When you read a cylinder at a time, that makes a smaller blocksize less of an issue for the DS work.

Thanks, -Carrie

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