Message-ID: <1392587c-c56a-2816-e3cf-4202a216a3be@enterprisedb.com>
Date: Tue, 8 Mar 2022 14:48:54 +0100
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Subject: Re: WIP: WAL prefetch (another approach)
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To: Thomas Munro <thomas.munro@gmail.com>,
 Ashutosh Sharma <ashu.coek88@gmail.com>
Cc: Daniel Gustafsson <daniel@yesql.se>, Stephen Frost <sfrost@snowman.net>,
 Alvaro Herrera <alvherre@2ndquadrant.com>, Andres Freund
 <andres@anarazel.de>, David Steele <david@pgmasters.net>,
 Dmitry Dolgov <9erthalion6@gmail.com>, Jakub Wartak
 <Jakub.Wartak@tomtom.com>, Tom Lane <tgl@sss.pgh.pa.us>,
 Tomas Vondra <tomas.vondra@2ndquadrant.com>,
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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
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On 3/8/22 06:15, Thomas Munro wrote:
> On Wed, Dec 29, 2021 at 5:29 PM Thomas Munro <thomas.munro@gmail.com> wrote:
>> https://github.com/macdice/postgres/tree/recovery-prefetch-ii
> 
> Here's a rebase.  This mostly involved moving hunks over to the new
> xlogrecovery.c file.  One thing that seemed a little strange to me
> with the new layout is that xlogreader is now a global variable.  I
> followed that pattern and made xlogprefetcher a global variable too,
> for now.
> 
> There is one functional change: now I block readahead at records that
> might change the timeline ID.  This removes the need to think about
> scenarios where "replay TLI" and "read TLI" might differ.  I don't
> know of a concrete problem in that area with the previous version, but
> the recent introduction of the variable(s) "replayTLI" and associated
> comments in master made me realise I hadn't analysed the hazards here
> enough.  Since timelines are tricky things and timeline changes are
> extremely infrequent, it seemed better to simplify matters by putting
> up a big road block there.
> 
> I'm now starting to think about committing this soon.

+1. I don't have the capacity/hardware to do more testing at the moment,
but all of this looks reasonable.


regards

-- 
Tomas Vondra
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