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Archives of the TeradataForum
Message Posted: Tue, 15 Nov 2005 @ 18:28:00 GMT
| Subj: | | Re: Diagnostic Lookahead |
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| From: | | Anomy Anom |
<-- Anonymously Posted: Tuesday, November 15, 2005 10:58 -->
The correct syntax is
diagnostic "lookahead=1" on for session;
substitute 5 in place of 1, if you need to force 5-lookahead. As you might be aware, optimizer first tries 1-lookahead, 5-lookahead and
the large table/small table join optimization. At some point of the 5-lookahead plan, if it finds, that it is costlier than 1-lookahead, it
basically aborts this 5-lookahead. In such cases, to force this plan, we use this diagnostic. This diagnostic is more of an internal use for
trying different joinplans. More information on the lookahead plans can be found in SQL reference, Statement and Transaction processing.
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