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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: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Cc: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(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 14:10:42
Message-ID: 1242396642.3843.754.camel@ebony.2ndQuadrant (view raw or flat)
Thread:
Lists: pgsql-bugspgsql-hackers
On Fri, 2009-05-15 at 22:56 +0900, Fujii Masao wrote:

> OK, I probably understood your point. The timeline history files whose
> timeline ID is larger than that of an oldest backup must not be deleted
> from the archive. On the other hand, the smaller or equal one can be
> deleted. Not all history files are necessary. So, if we don't keep older
> backup, we probably can delete all files in the archive before
> pg_start_backup().
> Is my understanding right?

Heikki is right in one sense: if you do pg_start_backup() then for
*that* backup you do not need earlier files. 

However, as you have pointed out, if you have *multiple* backups then
deleting history files may cause problems with an earlier backup.

It's standard practice to have >1 backup, so there is potential for
error and minimum is we must document that. 

Rather than explaining the problem and the rules by which we can work
out exactly which history files to keep, I think it is safer to say that
we must keep all history files.

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


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