| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | "Bossart, Nathan" <bossartn(at)amazon(dot)com> |
| Cc: | "alvherre(at)alvh(dot)no-ip(dot)org" <alvherre(at)alvh(dot)no-ip(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, "x4mmm(at)yandex-team(dot)ru" <x4mmm(at)yandex-team(dot)ru>, "a(dot)lubennikova(at)postgrespro(dot)ru" <a(dot)lubennikova(at)postgrespro(dot)ru>, "hlinnaka(at)iki(dot)fi" <hlinnaka(at)iki(dot)fi>, "matsumura(dot)ryo(at)fujitsu(dot)com" <matsumura(dot)ryo(at)fujitsu(dot)com>, "masao(dot)fujii(at)gmail(dot)com" <masao(dot)fujii(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: archive status ".ready" files may be created too early |
| Date: | 2021-08-31 20:29:29 |
| Message-ID: | 20210831202929.3f3jzlzowis4g7gu@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2021-08-31 18:09:36 +0000, Bossart, Nathan wrote:
> On 8/31/21, 10:21 AM, "Andres Freund" <andres(at)anarazel(dot)de> wrote:
> > What would trigger the flushing? We don't write out partially filled pages
> > unless
> > a) we're explicitly flushing an LSN on the partial page (e.g. because a
> > synchronous commit record resides on it)
> > b) there's an async commit (i.e. commit with synchronous_commit=off) on the
> > page
>
> Ah, so your point is that an open transaction that has written a
> partial page on the next segment wouldn't trigger a flush.
Doesn't have to be a transaction, can be a checkpoint or xl_running_xacts, or
... as well.
> What appears to happen in this case is that bgwriter eventually creates a
> xl_running_xacts record and nudges walwriter to flush it to disk, at which
> point the .ready file(s) will be created. That's admittedly a bit fragile.
That's not guaranteed to happen. If e.g. the partial record is a checkpoint or
a xl_running_xacts, we'll not trigger further WAL writes in the background,
unless autovacuum ends up doing something.
Regards,
Andres
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