From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "Gurjeet Singh" <singh(dot)gurjeet(at)gmail(dot)com> |
Cc: | "PGSQL Hackers" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Optimizer sorting an already sorted result |
Date: | 2008-04-30 02:02:04 |
Message-ID: | 12174.1209520924@sss.pgh.pa.us |
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"Gurjeet Singh" <singh(dot)gurjeet(at)gmail(dot)com> writes:
> In the plan below, we can see that the optimizer is sorting an already
> sorted result. It seems to forget the sort order across the UNIQUE node. My
> question is, do we make any attempts in the optimizer to remember the sort
> order of a result, to avoid any further sorting on same sort-key? If not,
> can we do something about it?
Per the comment in create_unique_path:
/*
* Treat the output as always unsorted, since we don't necessarily have
* pathkeys to represent it.
*/
pathnode->path.pathkeys = NIL;
No doubt this could be improved, but I'm unsure about the effort/reward
ratio.
regards, tom lane
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