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Message Posted: Thu, 03 Oct 2002 @ 00:42:16 GMT


     
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Subj:   Synchronous scanning
 
From:   David Wellman

Frank,

Synchronized scanning is Teradata's ability to use the same i/o to a data block to satisfy multiple queries.

Say you have two queries which are running concurrently and that each query's join plan includes a full table scan of a particular table. When the AMP step (for a particular query) that performs a table scan starts Teradata looks to see if there are any other queries which are also doing a scan of the same table. If there are, then the AMP step which has just started will read the same data blocks that are being read from disk for the already running query. This allows Teradata to utilise the same physical i/o to satisfy multiple queries.

There's a bit more to the process and explanation, but that's the basis of it.

Any more questions feel free to ask.


Cheers,

Dave

Ward Analytics Ltd: Information in motion (www.ward-analytics.com)



     
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