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From: Chapman Flack <chap@anastigmatix.net>
To: pgsql-hackers@lists.postgresql.org
Subject: Re: [HACKERS] AdvanceXLInsertBuffer vs. WAL segment compressibility
Date: Mon, 26 Mar 2018 07:30:10 -0400
Message-ID: <5AB8D9C2.2010208@anastigmatix.net> (raw)
In-Reply-To: <20180326032731.GM24540@tamriel.snowman.net>
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	<5A92F0C0.7070706@anastigmatix.net>
	<C0523BD1-485D-48B5-982E-8D63E2D001B7@yesql.se>
	<5AADB130.2020206@anastigmatix.net>
	<4597.1521338981@sss.pgh.pa.us>
	<46FFB930-B0F3-400A-85ED-D9948C97FADF@yesql.se>
	<5AAEE00E.9050503@anastigmatix.net>
	<21C25ED8-4ED8-4AD4-B551-3E3987ECB18F@yesql.se>
	<5AAEFF11.3070903@anastigmatix.net>
	<20180326032731.GM24540@tamriel.snowman.net>

On 03/25/18 23:27, Stephen Frost wrote:
>>  .travis.yml                          | 47 ++++++++++++++++++++++++++++++++++++
> 
> ... not something that I think we're going to add into the main tree.

Looks like that got in by mistake, sorry.

> -			AdvanceXLInsertBuffer(CurrPos, false);
> ...
> +			currpos = GetXLogBuffer(CurrPos);
>
> AdvanceXLInsertBuffer() does quite a bit, so I'm a bit surprised to see
> this simply removing that call, you're confident there's nothing done
> which still needs doing..?

My belief from looking at the code was that AdvanceXLInsertBuffer() is among
the things GetXLogBuffer() does, so calling both would result in two calls
to the former (which I don't believe would hurt, it would only
do enough work the second time to determine it had already been done).

However, it is done *conditionally* within GetXLogBuffer(), so it doesn't
hurt to have extra eyes reviewing my belief that the condition will be true
in this case (looping through tail blocks that haven't been touched yet).

-Chap




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