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Re: Slow pg_dump

From: "Phillip Smith" <phillip(dot)smith(at)weatherbeeta(dot)com(dot)au>
To: "'Ryan Wells'" <ryan(dot)wells(at)soapware(dot)com>,"'Tom Lane'" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: <pgsql-admin(at)postgresql(dot)org>
Subject: Re: Slow pg_dump
Date: 2008-04-14 23:26:10
Message-ID: 004b01c89e86$ebe8fbe0$9b0014ac@wbaus090 (view raw, whole thread or download thread mbox)
Lists: pgsql-admin
(Sorry, hit send too soon!)

> I ran pg_dump with the arguments you suggested, and my 4 GB test
> table finished backing up in about 25 minutes, which seems great.
> The only problem is that the resulting backup file was over 9 GB.
> Using -Z2 resulting in a 55 minute 6GB backup.
> Here's my interpretation of those results: the TOAST tables for
> our image files are compressed by Postgres.  During the backup,
> pg_dump uncompresses them, and if compression is turned on,
> recompresses the backup.  Please correct me if I'm wrong there.
> If we can't find a workable balance using pg_dump, then it looks
> like our next best alternative may be a utility to handle
> filesystem backups, which is a little scary for on-site,
> user-controlled servers.

How about a post-backup compress?
	pg_dump -Z0 > uncompressed-backup.sql
	gzip uncompressed-backup.sql
	mv uncompressed-backup.sql.gz compressed-backup.sql.gz

Your backup is completed in reasonable time, you're just handling
the storage of the backup afterwards, while users can be using the
System again...

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