| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, Alex Hunsaker <badalex(at)gmail(dot)com>, Kenneth Marshall <ktm(at)rice(dot)edu>, Xiao Meng <mx(dot)cogito(at)gmail(dot)com>, Zdenek Kotala <Zdenek(dot)Kotala(at)sun(dot)com>, pgsql-patches(at)postgresql(dot)org |
| Subject: | Re: hash index improving v3 |
| Date: | 2008-09-23 13:34:39 |
| Message-ID: | 1222176879.4445.361.camel@ebony.2ndQuadrant |
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| Lists: | pgsql-hackers pgsql-patches |
On Tue, 2008-09-23 at 09:13 -0400, Tom Lane wrote:
> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> > Thinks: Why not just sort all of the time and skip the debate entirely?
>
> The sort is demonstrably a loser for smaller indexes. Admittedly,
> if the index is small then the sort can't cost all that much, but if
> the (correct) threshold is some large fraction of shared_buffers then
> it could still take awhile on installations with lots-o-buffers.
The other realisation is that for large indexes, giving them more
maintenance_work_mem probably will make them build faster 'cos we'll be
sorting. So "give big indexes more memory" is still true *enough* to be
broadly consistent, explainable and understandable. I do explain things
in more detail on some courses, but pithy rules help busy people.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
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