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on-line backup questions

From: Tom Davies <tgdavies(at)gmail(dot)com>
To: pgsql-admin(at)postgresql(dot)org
Subject: on-line backup questions
Date: 2007-12-22 02:02:50
Message-ID: 0FBA939C-2ED1-4400-BD3B-5290193837D0@gmail.com (view raw or flat)
Thread:
Lists: pgsql-admin
I've been working on backup restore scripts for a PostgreSQL DB hosted  
on an Amazon EC2 instance. EC2 instances don't have any persistent  
storage, so I archive the WAL files to Amazon S3. I do periodic  
backups, and restore and roll forward when an instance is restarted.

I've followed the excellent documentation at http://www.postgresql.org/docs/8.0/interactive/backup-online.html 
  , and everything is working well, but I have a few further questions.

1. Purely out of curiousity, what's the nnnnnnnn.history file which is  
requested from the archive when you restore? I realise that the  
restore process looking for files which don't exist is not a problem,  
I'm just being inquisitive.

2. When I do a backup, Postgres requests archiving of n.m.backup and  
the WAL file n immediately, so I only copy WAL files with numbers > n  
from pg_xlog. I've seen suggestions that I should be copying WAL files  
with numbers >= n -- is there any reason to do so?

3. What's the best thing to do when I deliberately shut down  
PostgreSQL (i.e. pg_ctl stop)? When I start again I will be restoring  
from the most recent backup and rolling forward over the archived WAL  
files. I believe that shutdown leaves me with unarchived WAL files in  
pg_xlog. Can I simply copy these to S3 as if they were WAL files which  
were copied from pg_xlog at the time of the last backup, and then put  
them back into pg_xlog as part of my restore process?

4. I'm using PostgreSQL 8.0 -- are there any significant improvements  
in on-line backups in later versions?

Thanks,
   Tom

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Subject: Re: on-line backup questions
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