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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Stephen Frost <sfrost@snowman.net>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: David Steele <david@pgmasters.net>
Cc: Andres Freund <andres@anarazel.de>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: WIP: WAL prefetch (another approach)
Date: Thu, 6 Aug 2020 12:47:01 +0200
Message-ID: <20200806104701.j3xnkczd6qelfnhj@development> (raw)
In-Reply-To: <CA+hUKGKfsWj+4qPfOkC4YtYtVO33yrCty1uWxBp3R1OSqWEcyA@mail.gmail.com>
References: <20200419114820.h62ryte7uwu46e2x@localhost>
	<CA+hUKGJ7_niJzcCHX5JWFo-05pLbzwukQfFgQi4-h46yZh=tqA@mail.gmail.com>
	<20200425191935.4p6qxzzu5bklodwk@localhost>
	<20200502151423.yf52i63u232fdfrg@localhost>
	<CA+hUKG+obB-e_VFa2uPVe52DvtpBQtC30vyo_PDURJQTr3SdJQ@mail.gmail.com>
	<20200605223422.r76a5rpl2zg2xo34@development>
	<20200606003632.GS6680@tamriel.snowman.net>
	<CA+hUKG+oXRpmc=yOM-GCQMt+Q4GPt9dD_idhPhFVf6f=_owwvA@mail.gmail.com>
	<20200803154659.nzf5qzuozts5dujp@development>
	<CA+hUKGKfsWj+4qPfOkC4YtYtVO33yrCty1uWxBp3R1OSqWEcyA@mail.gmail.com>

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.vondra@2ndquadrant.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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  Cc: tomas.vondra@2ndquadrant.com, thomas.munro@gmail.com, sfrost@snowman.net, 9erthalion6@gmail.com, david@pgmasters.net, andres@anarazel.de, alvherre@2ndquadrant.com
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