| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, Luke Lonergan <llonergan(at)greenplum(dot)com>, pgsql-patches(at)postgresql(dot)org, Martijn van Oosterhout <kleptog(at)svana(dot)org>, Qingqing Zhou <zhouqq(at)cs(dot)toronto(dot)edu>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: [HACKERS] Automatically setting work_mem |
| Date: | 2006-04-22 17:17:08 |
| Message-ID: | 7589.1145726228@sss.pgh.pa.us |
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| Lists: | pgsql-hackers pgsql-patches |
Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> I still do, for multi-user systems. Releasing unused memory from a large
> CREATE INDEX will allow that memory to be swapped out, even if the brk
> point can't be changed.
Say what? It can get "swapped out" anyway, whether we free() it or not.
More to the point, though: I don't believe that the proposed patch is a
good idea --- it does not reduce the peak sortmem use, which I think is
the critical factor for a multiuser system, and what it does do is
reduce the locality of access to the sort temp file during the merge
phases. That will definitely have some impact; maybe small, but some;
and I don't see where the benefit comes in.
regards, tom lane
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