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Message Posted: Fri, 03 Oct 2003 @ 18:11:42 GMT


     
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Subj:   Re: Plastic Steps
 
From:   Anomy Anom

<-- Anonymously Posted: Friday, October 03, 2003 11:48 -->

The default on new machines for MaxParseTreeSegs is 1000. When the machines came in we changed it to 64 to match the old machines. Since upgrading to V2R4.1, a problem arose when determining bundling sizes for out OLTP application. NCR said it should be set to 1000, not giving an explanation but just saying that it is the default. So we changed it to 1000 and were getting 3712's. Our StepsSegmentSize was set at 640. So we changed it to 1024 (the default) and the error went away.

Per the manual:

StepsSegmentSize
This is an enabling field rather than a performance enhancement field. When decomposing a Teradata SQL statement, the parser generates plastic steps, which the AMPs then process. StepsSegmentSize defines the maximum size of each plastic steps segment.

Recommendation: Large values allow the parser to generate more SQL optimizer steps than the AMPs use to process more complex queries. Set this field to a small number to limit the query complexity. Set this field to 1024 KB for the maximum size allowable for plastic steps.

I think the documentation on these tunables is very lacking. The ramification for changing these value is not given. I feel like we are blindly changing tunables just to make it work, not knowing what the real impact may be.

-The originator of this thread



     
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