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Re: [HACKERS] Re: BUG #4796: Recovery followed by backup creates unrecoverable WAL-file

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Mikael Krantz <mk(at)zigamorph(dot)se>, pgsql-bugs(at)postgresql(dot)org, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] Re: BUG #4796: Recovery followed by backup creates unrecoverable WAL-file
Date: 2009-05-15 19:40:05
Message-ID: 1242416405.3843.840.camel@ebony.2ndQuadrant (view raw or flat)
Thread:
Lists: pgsql-bugspgsql-hackers
On Fri, 2009-05-15 at 18:46 +0300, Heikki Linnakangas wrote:

> Well, we already have this in the docs:
> 
> > Each time a new timeline is created, PostgreSQL creates a "timeline
> history" file that shows which timeline it branched off from and when.
> These history files are necessary to allow the system to pick the
> right WAL segment files when recovering from an archive that contains
> multiple timelines. Therefore, they are archived into the WAL archive
> area just like WAL segment files. The history files are just small
> text files, so it's cheap and appropriate to keep them around
> indefinitely (unlike the segment files which are large). You can, if
> you like, add comments to a history file to make your own notes about
> how and why this particular timeline came to be. Such comments will be
> especially valuable when you have a thicket of different timelines as
> a result of experimentation.
> 
> What exactly do you want to change? Patch, please.

I find this exchange between us quite strange. The discussion on this
thread has been fairly clear. Fujii-san and myself have both asked for
it to be documented that history files should not be deleted.

The above section says it's "appropriate to keep them around
indefinitely".

What it doesn't say is if you delete them then you can experience
problems in certain circumstances, so we advise strongly not do this. It
would be even better if there was a section on remvong files from the
archive.

Do I really need to write a patch to say that, have you formally review
it, then change the wording to what you would have written in the first
place and then commit? Really? How many years do all of us have to work
together before we develop an efficient process for trivial changes such
as this?

-- 
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support


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