[linux-lvm] PostgreSQL and file system level backup

Ragnar Kjørstad lvm at ragnark.vestdata.no
Fri Nov 15 20:11:02 UTC 2002

On Fri, Nov 15, 2002 at 04:25:49PM -0500, Murthy Kambhampaty wrote:
> "Unless the postmaster is shut down meanwhile, you'll probably end up with a
> corrupt database.  The problem is that xfsdump does not give you an
> instantaneous snapshot of the filesystem state, so you will probably collect
> inconsistent contents of the various files that make up the database."
> Which gives rise to my present question: given that LVM DOES give an
> instantaneous snapshot of the filesystem, would an xfsdump of an LVM
> snapshot of an XFS filesystem give usable backups?

Yes, it should.

Allthough, some of the postgresql-developers use the term "corrupt
database" of a database where the table-files are inconsistant. That's
generally _always_ the case when the server is running, as the latest
updates are only available in the database-log. That's also the case for
the LVM-snapshot.

This "inconsistancy" will be fixed by log-replay when you start the server
(after restore).

If you want to avoid it, you can:
- shut down databasee
- take snapshot
- start database
- backup from snapshot

There was a long thread on this subject on the postgresql-list a month
or two ago.

Ragnar Kjørstad
Big Storage

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