From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Curt Sampson <cjs(at)cynic(dot)net> |
Cc: | Markus Wollny <Markus(dot)Wollny(at)computec(dot)de>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: One source of constant annoyance identified |
Date: | 2002-06-30 03:39:35 |
Message-ID: | 17692.1025408375@sss.pgh.pa.us |
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Lists: | pgsql-general |
Curt Sampson <cjs(at)cynic(dot)net> writes:
> On Fri, 28 Jun 2002, Tom Lane wrote:
>> And the swapping activity is exactly the problem, isn't it?
> That particular swapping activity would not be a problem. Memory
> that's not used gets paged out and that's the end of it. The problem
> is that something is *using* that memory, so it's not being paged
> out, or if it does get paged out, it gets paged back in again.
Yeah --- but typical implementations of malloc are very pager-
unfriendly; they tend to traverse data structures that consist
of a word or two at the head of each randomly-sized chunk of
data or former-now-freed data.
PG adds its own layer of not-very-paging-friendly allocation
logic on top of whatever sins your local malloc may commit.
Bottom line is that a PG backend that's swollen to a couple
hundred MB is trouble. Don't assume it'll play nice with the
swapper; it won't.
regards, tom lane
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