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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: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Reducing size of WAL record headers
Date: 2013-01-09 21:17:25
Message-ID: CA+U5nMJZxnS7zqtY2-ReRL62wHdUDXdQKWr-3feB50nP9An5KQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 9 January 2013 20:54, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> wrote:

> Here's a better idea:
>
> Let's keep xl_tot_len as it is, but move xl_len at the very end of the WAL
> record, after all the backup blocks. If there are no backup blocks, xl_len
> is omitted. Seems more robust to keep xl_tot_len, so that you require less
> math to figure out where one record ends and where the next one begins.

OK, I avoided tampering with xl_len cos its so widely used. Will look.

>> Forcing the XLogRecord header to be all on one page makes the format
>> more robust and simplifies the code that copes with header wrapping.

> -1 on that. That would essentially revert the changes I made earlier.

OK, idea dropped.

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


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