> 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
littlescary for on-site, user-controlled servers.

Ryan

-----Original Message-----
From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Sent: Saturday, April 12, 2008 9:46 PM
To: Ryan Wells
Cc: pgsql-admin@postgresql.org
Subject: Re: [ADMIN] Slow pg_dump

"Ryan Wells" <ryan.wells@soapware.com> writes:
> We have several tables that are used to store binary data as bytea (in

> this example image files),

Precompressed image formats, no doubt?

> pg_dump -i -h localhost -p 5432 -U postgres -F c -v -f
> "backupTest.backup" -t "public"."images" db_name

Try it with -Z0, or even drop the -Fc completely, since it's certainly not
very helpful on a single-table dump. Re-compressing already compressed data
is not only useless but impressively slow ...

Also, drop the -i, that's nothing but a foot-gun.

regards, tom lane

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