Subject: .backup files not needed?

From: Simon Riggs <[email-masked]>
Date: Fri, 09 May 2008 07:51:53 +0100

Just had questions from a replication user about why the .backup file is
described as "can ordinarily be ignored" and is considered optional by
recovery also even when pg_start_backup() was used.

If the file was created, it is necessary to use it in recovery, so
should never be ignored as the docs imply.

Can we remove the phrase ", and can ordinarily be ignored." ? from
doc/src/sgml/backup.sgml

  <para>
    To make use of the backup, you will need to keep around all the WAL
    segment files generated during and after the file system backup.
    To aid you in doing this, the <function>pg_stop_backup</> function
    creates a <firstterm>backup history file</> that is immediately
    stored into the WAL archive area. This file is named after the first
    WAL segment file that you need to have to make use of the backup.
    For example, if the starting WAL file is
    <literal>0000000100001234000055CD</> the backup history file will be
    named something like
    <literal>0000000100001234000055CD.007C9330.backup</>. (The second
    part of the file name stands for an exact position within the WAL
    file, and can ordinarily be ignored.) Once you have safely archived
    the file system backup and the WAL segment files used during the
    backup (as specified in the backup history file), all archived WAL
    segments with names numerically less are no longer needed to recover
    the file system backup and can be deleted. However, you should
    consider keeping several backup sets to be absolutely certain that
    you can recover your data.
   </para>

-- 
  Simon Riggs
  2ndQuadrant  http://www.2ndQuadrant.com

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From: Tom Lane <[email-masked]>
Date: Fri, 09 May 2008 10:28:28 -0400

> recovery also even when pg_start_backup() was used.

What it says is that the second part of the filename can ordinarily
be ignored.  I don't know why neither he nor you managed to parse the
sentence correctly.  Feel free to propose a rewording, but removing
information doesn't sound like a solution.

			regards, tom lane

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From: Bruce Momjian <[email-masked]>
Date: Fri, 9 May 2008 10:35:24 -0400 (EDT)

>     you can recover your data.

The comment is saying "the second part of the file name" can be ignored,
not the backup file itself.

-- 
  Bruce Momjian  <[email-masked]>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

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From: Simon Riggs <[email-masked]>
Date: Fri, 09 May 2008 15:43:09 +0100

> information doesn't sound like a solution.

Its probably best to read the whole mail before commenting on other
people's parsing. ;-)

I'll do a patch.

---

From: Simon Riggs <[email-masked]>
Date: Fri, 09 May 2008 15:49:17 +0100

> not the backup file itself.

Yes, I know. I'm asking if anyone minds me changing the docs to make it
clearer, not being confused by it myself. The issue was raised because
pg_standby doesn't treat the file as optional, though recovery code
does.