Date: Fri, 22 Nov 2019 10:35:51 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Antonin Houska <ah@cybertec.at>
Cc: Michael Paquier <michael@paquier.xyz>,
	Thomas Munro <thomas.munro@gmail.com>,
	Robert Haas <robertmhaas@gmail.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: Attempt to consolidate reading of XLOG page
Message-ID: <20191122133551.GA4216@alvherre.pgsql>
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On 2019-Nov-22, Antonin Houska wrote:

> I thought that in [1] you try discourage me from using pg_pread(), but now it
> seems to be the opposite. Ideally I'd like to see no overhead added by my
> patch at all, but the code simplicity should matter too.

FWIW I think the new code is buggy because it doesn't seem to be setting
ws_off, so I suppose the optimization in ReadPageInternal to skip
reading the page when it's already the page we have is not hit, except
for the first page in the segment.  I didn't verify this, just my
impression while reading the code.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services