From: alvherre@alvh.no-ip.org <alvherre@alvh.no-ip.org>
To: Bossart, Nathan <bossartn@amazon.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: x4mmm@yandex-team.ru <x4mmm@yandex-team.ru>
Cc: a.lubennikova@postgrespro.ru <a.lubennikova@postgrespro.ru>
Cc: hlinnaka@iki.fi <hlinnaka@iki.fi>
Cc: matsumura.ryo@fujitsu.com <matsumura.ryo@fujitsu.com>
Cc: masao.fujii@gmail.com <masao.fujii@gmail.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: archive status ".ready" files may be created too early
Date: Fri, 20 Aug 2021 17:38:16 -0400
Message-ID: <202108202138.scohxwoyflcp@alvherre.pgsql> (raw)
In-Reply-To: <029A2429-21B1-426F-A8FE-109ADF6A8E90@amazon.com>
On 2021-Aug-20, Bossart, Nathan wrote:
> > On Fri, Aug 20, 2021 at 1:29 PM Bossart, Nathan <bossartn@amazon.com> wrote:
> >> This led me to revisit the two-element
> >> approach that was discussed upthread. What if we only stored the
> >> earliest and latest segment boundaries at any given time? Once the
> >> earliest boundary is added, it never changes until the segment is
> >> flushed and it is removed. The latest boundary, however, will be
> >> updated any time we register another segment. Once the earliest
> >> boundary is removed, we replace it with the latest boundary. This
> >> strategy could cause us to miss intermediate boundaries, but AFAICT
> >> the worst case scenario is that we hold off creating .ready files a
> >> bit longer than necessary.
> I've attached a patch to demonstrate what I'm thinking.
There is only one thing I didn't like in this new version, which is that
we're holding info_lck too much. I've seen info_lck contention be a
problem in some workloads and I'd rather not add more stuff to it. I'd
rather we stick with using a new lock object to protect all the data we
need for this job.
Should this new lock object be a spinlock or an lwlock? I think a
spinlock would generally be better because it's lower overhead and we
can't use it in shared mode anywhere, which would be the greatest
argument for an lwlock. However, I think we avoid letting code run with
spinlocks held that's not straight-line code, and we have some function
calls there.
--
Álvaro Herrera Valdivia, Chile — https://www.EnterpriseDB.com/
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To: pgsql-hackers@postgresql.org
Cc: alvherre@alvh.no-ip.org, bossartn@amazon.com, robertmhaas@gmail.com, horikyota.ntt@gmail.com, x4mmm@yandex-team.ru, a.lubennikova@postgrespro.ru, hlinnaka@iki.fi, matsumura.ryo@fujitsu.com, masao.fujii@gmail.com
Subject: Re: archive status ".ready" files may be created too early
In-Reply-To: <202108202138.scohxwoyflcp@alvherre.pgsql>
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