From: Tom Lane <tgl@sss.pgh.pa.us>
To: "David G. Johnston" <david.g.johnston@gmail.com>
cc: Wells Oliver <wells.oliver@gmail.com>,
        pgsql-admin <pgsql-admin@postgresql.org>
Subject: Re: temp_buffers and work_mem and big temp tables
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Comments: In-reply-to "David G. Johnston" <david.g.johnston@gmail.com>
	message dated "Tue, 10 Nov 2020 12:04:36 -0700"
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Date: Tue, 10 Nov 2020 14:32:17 -0500
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"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Tuesday, November 10, 2020, Wells Oliver <wells.oliver@gmail.com> wrote:
>> Hey all: I was wondering if someone might spell out which setting has more
>> impact on temporary tables being stored in memory versus disk? I have read
>> the docs but I thought I'd reach out and ask the community: I keep
>> increasing both in some scripts where Large Temp Tables are created, but
>> I'm wondering if it's more efficient just to use one or the other.

> IIUC work_mem has nothing to do with temporary tables.  All tables have a
> disk component and read/writes are done via buffers.

The temp_buffers setting controls how much temporary-table data can be
kept in a session's memory.  If you get to more than that, it spills out
to disk (or at least to the kernel's disk buffers).

			regards, tom lane