Re: BUG #15115: temporary AND unlogged tables for parallel db import

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Enno Wein <ennowein(at)yahoo(dot)com>
Cc: Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, pgsql-bugs(at)lists(dot)postgresql(dot)org
Subject: Re: BUG #15115: temporary AND unlogged tables for parallel db import
Date: 2018-03-16 17:00:58
Message-ID: 24377.1521219658@sss.pgh.pa.us
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Enno Wein <ennowein(at)yahoo(dot)com> writes:
> Every session (72 for now) creates and drops several (temp-) tables and
> indexes. Every session runs for about 30min, then does a final insert
> and exits afterwards.
> Depending on parallelism chosen, we run 8, 16 or 24 sessions in parallel.
> The main, (global-) table which persists has been declared as either
> logged or unlogged, there is much WAL traffic in any case.

That still sounds like it'd just add up to a few temp table creations/
deletions per minute, which would not account for any huge volume of
WAL traffic. I'm suspicious that somewhere you've got activity going
into a table that you forgot to make temp or unlogged.

You might grab pg_xlogdump or a logical decoding tool and look into
the WAL stream to see exactly what's going by.

regards, tom lane

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