Re: Excessive WAL generation and related performance issue

From: Joe Conway <mail(at)joeconway(dot)com>
To: Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Hackers (PostgreSQL)" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Excessive WAL generation and related performance issue
Date: 2014-04-15 21:21:53
Message-ID: 534DA2F1.4000606@joeconway.com
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On 04/15/2014 02:15 PM, Heikki Linnakangas wrote:
> You're counting XLogRecData structs, not backup blocks. Each
> backup block typically consists of three XLogRecData structs, one
> to record a BkpBlock struct, one to record the data before the
> unused "hole" in the middle of the page, and one for after.
> Sometimes just two, if there is no hole to skip. See the loop just
> before the CRC calculation, that's where the XLogRecData entries
> for backup blocks are created.
>
> - Heikki

Ah, thanks for the explanation!

Joe

- --
Joe Conway
credativ LLC: http://www.credativ.us
Linux, PostgreSQL, and general Open Source
Training, Service, Consulting, & 24x7 Support
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