Re: Postgres, fsync, and OSs (specifically linux)

From: Andres Freund <andres(at)anarazel(dot)de>
To: Dmitry Dolgov <9erthalion6(at)gmail(dot)com>
Cc: Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Craig Ringer <craig(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Postgres, fsync, and OSs (specifically linux)
Date: 2018-05-22 16:47:40
Message-ID: 20180522164740.hg7gtkglycbto636@alap3.anarazel.de
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On 2018-05-22 08:57:18 -0700, Andres Freund wrote:
> Hi,
>
>
> On 2018-05-22 17:37:28 +0200, Dmitry Dolgov wrote:
> > Thanks for the patch. Out of curiosity I tried to play with it a bit.
>
> Thanks.
>
>
> > `pgbench -i -s 100` actually hang on my machine, because the
> > copy process ended up with waiting after `pg_uds_send_with_fd`
> > had
>
> Hm, that had worked at some point...
>
>
> > errno == EWOULDBLOCK || errno == EAGAIN
> >
> > as well as the checkpointer process.
>
> What do you mean with that latest sentence?
>
>
> > Looks like with the default
> > configuration and `max_wal_size=1GB` it writes more than reads to a
> > socket, and a buffer eventually becomes full.
>
> That's intended to then wake up the checkpointer immediately, so it can
> absorb the requests. So something isn't right yet.

Doesn't hang here, but it's way too slow. Reason for that is that I've
wrongly resolved a merge conflict. Attached is a fixup patch - does that
address the issue for you?

Greetings,

Andres Freund

Attachment Content-Type Size
0001-Fix-and-improve-pg_atomic_flag-fallback-implementati.patch text/x-diff 4.4 KB

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