Re: Status of DISTINCT-by-hashing work

<div dir="ltr">Sounds very much like 80% 20% story. 80% that was easy to do is done and now 20% that is complex and
progressis slow is left to be done. Sounds very familiar from the comment in plan cache invalidation :)<br /><br /><div
class="gmail_quote">OnTue, Aug 5, 2008 at 5:51 PM, Tom Lane <span dir="ltr"><<a
href="mailto:tgl@sss.pgh.pa.us">tgl@sss.pgh.pa.us</a>></span>wrote:<br /><blockquote class="gmail_quote"
style="border-left:1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> I've pretty much
finishedthe project I got a bee in my bonnet about<br /> last week, which is to teach SELECT DISTINCT how to
(optionally)use<br /> hashing for grouping in the same way that GROUP BY has been able to do<br /> for awhile.<br /><br
/>There are still two places in the system that hard-wire the use of<br /> sorting for duplicate elimination:<br /><br
/>* Set operations (UNION/INTERSECT/EXCEPT)<br /><br /> * Aggregate functions with DISTINCT<br /><br /> I'm thinking of
tryingto fix set operations before I leave this topic,<br /> but I'm not sure it's worth the trouble to change DISTINCT
aggregates.<br/> They'd be a lot more work (since there's no executor infrastructure<br /> in place that could be used)
andthe return on investment seems low.<br /><br /> Comments?<br /><br />                        regards, tom lane<br
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