Re: WIP: WAL prefetch (another approach)

From: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
To: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
Cc: Stephen Frost <sfrost(at)snowman(dot)net>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, David Steele <david(at)pgmasters(dot)net>, Andres Freund <andres(at)anarazel(dot)de>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: WIP: WAL prefetch (another approach)
Date: 2020-08-06 10:47:01
Message-ID: 20200806104701.j3xnkczd6qelfnhj@development
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On Thu, Aug 06, 2020 at 02:58:44PM +1200, Thomas Munro wrote:
>On Tue, Aug 4, 2020 at 3:47 AM Tomas Vondra
><tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>> On Thu, Jul 02, 2020 at 03:09:29PM +1200, Thomas Munro wrote:
>> >FYI I am still trying to reproduce and understand the problem Tomas
>> >reported; more soon.
>>
>> Any luck trying to reproduce thigs? Should I try again and collect some
>> additional debug info?
>
>No luck. I'm working on it now, and also trying to reduce the
>overheads so that we're not doing extra work when it doesn't help.
>

OK, I'll see if I can still reproduce it.

>By the way, I also looked into recovery I/O stalls *other* than
>relation buffer cache misses, and created
>https://commitfest.postgresql.org/29/2669/ to fix what I found. If
>you avoid both kinds of stalls then crash recovery is finally CPU
>bound (to go faster after that we'll need parallel replay).

Yeah, I noticed. I'll take a look and do some testing in the next CF.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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