| 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 17:18:36 |
| Message-ID: | 20210831171836.ww43agvczffdultp@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2021-08-31 17:01:31 +0000, Bossart, Nathan wrote:
> > If the record ending at s4 + 10 isn't an async commit (and thus
> > XLogCtl->asyncXactLSN is smaller), and there are no further records, we can
> > end up waiting effectively forever for s2 (and s3) to be archived. If all
> > other connections (and autovac etc) are idle, there will be no XLogFlush()
> > calls, nor will XLogBackgroundFlush() do anything, because it'll hit the "If
> > already known flushed" path, because the the first page in s4 is only
> > partially filled.
>
> I'm not following why s4 wouldn't be flushed in this example. Even if
> the first page in s4 is only partially filled, that portion of the
> record should still get flushed, and we'll create the .ready files for
> s2 and s3 at that time.
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
Greetings,
Andres Freund
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