Re: [REVIEW] Re: Compression of full-page-writes

From: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
To: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Cc: Rahila Syed <rahilasyed90(at)gmail(dot)com>, Rahila Syed <rahilasyed(dot)90(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [REVIEW] Re: Compression of full-page-writes
Date: 2014-11-11 08:10:01
Message-ID: CAB7nPqQeinmb1RPGq=r__kJHdpihnjpp_09-WssfpoyDuMqPmA@mail.gmail.com
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On Mon, Nov 10, 2014 at 5:26 PM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> wrote:
> I'll go through the patch once again a bit later, but feel free to comment.
Reading again the patch with a fresher mind, I am not sure if the
current approach taken is really the best one. What the patch does now
is looking at the header of the first backup block, and then
compresses the rest, aka the other blocks, up to 4, and their headers,
up to 3. I think that we should instead define an extra bool flag in
XLogRecord to determine if the record is compressed, and then use this
information. Attaching the compression status to XLogRecord is more
in-line with the fact that all the blocks are compressed, and not each
one individually, so we basically now duplicate an identical flag
value in all the backup block headers, which is a waste IMO.
Thoughts?
--
Michael

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