Feature Requests item #2220597, was opened at 2008-11-04 13:07 Message generated for change (Comment added) made by mlkersten You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=482471&aid=2220597&group_id=56967
Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: SQL - general Group: None Status: Open Priority: 5 Private: No Submitted By: Stefan de Konink (skinkie) Assigned to: Nobody/Anonymous (nobody) Summary: [Performance] Reduce duplicate subqueries in one query Initial Comment: I think a significant performance gain can be achieved if the SQL parser would 'deduplicate' equal subqueries. The most trivial scenario would be a 'union all' with 10 equal queries next to eachother. The amount of time taken for processing this query (measured by more than 450 attributes) seems to be equal to executing each query individually. With my naive knowledge I think a programmer would 'assume' an atomic query. Hence all different subqueries should result in the same result under the hood. Now one could argue, deduplicate at layer 8 ;) True; But it would a nifty feature if one could just get the optimization from SQL without changing queries that were explicitly executed in this sequence to align with previous results. ---------------------------------------------------------------------- >Comment By: Martin Kersten (mlkersten) Date: 2008-11-18 14:13 Message: The commenterm expression optimizer is on by default. A snippet of your code to ensure that the plans are indeed not recognized are welcome. ---------------------------------------------------------------------- Comment By: Stefan de Konink (skinkie) Date: 2008-11-18 11:08 Message: @Martin; Should it be explicitly enabled? Because I highly doubt it is working. @Fabian; Of course I could catch it in the program that is actually dynamically generating the mess. But the thing is I want it to be simple to process the output. ---------------------------------------------------------------------- Comment By: Martin Kersten (mlkersten) Date: 2008-11-18 09:55 Message: if the subquery is really identical then the MAL optimizer will/should catch it. And the recycler would further reduce the work as well. ---------------------------------------------------------------------- Comment By: Fabian (mr-meltdown) Date: 2008-11-18 09:39 Message: Perhaps it is easier to use the USING SELECT xxx AS y SELECT * FROM y UNION SELECT * FROM y; or similar syntax. (I'm not sure if I got the syntax right.) ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=482471&aid=2220597&group_id=56967 ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Monetdb-bugs mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/monetdb-bugs
