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Re: Reducing size of WAL record headers

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Reducing size of WAL record headers
Date: 2013-01-09 21:15:16
Message-ID: CA+U5nMKF96EONecEj20M5buYk2-O0sc8H2wXcLbJytj=o3B=7w@mail.gmail.com (view raw or flat)
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On 9 January 2013 21:02, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> wrote:

>> OK, crazy idea, but can we just record xl_len as a difference against
>> xl_tot_len, and shorten the xl_len field?
>
>
> Hmm, so it would essentially be the length of all the backup blocks. perhaps
> rename it to xl_bkpblk_len.
>
> However, that would cap the total size of backup blocks to 64k. Which would
> not be enough with 32k BLCKSZ.

Since that requires a recompile anyway, why not make XLogRecord
smaller only for 16k BLCKSZ or less?

Problem if we do that is that xl_len is used extensively in _redo
routines, so its a much more invasive patch.

-- 
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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