Re: XLogArchivingActive

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andreas Pflug <pgadmin(at)pse-consulting(dot)de>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: XLogArchivingActive
Date: 2006-05-25 22:16:14
Message-ID: 16616.1148595374@sss.pgh.pa.us
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Andreas Pflug <pgadmin(at)pse-consulting(dot)de> writes:
> That's right, but my proposal would implicitely switch on archiving
> while backup is in progress, thus explicitely enabling/disabling
> archiving wouldn't be necessary.

I'm not sure you can expect that to work. The system is not built to
guarantee instantaneous response to mode changes like that.

>> BTW, I don't actually understand why you want this at all. If you're
>> not going to keep a continuing series of WAL files, you don't have any
>> PITR capability. What you're proposing seems like a bulky, unportable,
>> hard-to-use equivalent of pg_dump. Why not use pg_dump?

> Because pg_dump will take too long and create bloated dump files. All I
> need is a physical backup for disaster recovery purposes without
> bringing down the server.

> In my case, I'd expect a DB that uses 114GB on disk to consume 1.4TB
> when pg_dumped, too much for the available backup capacity (esp.
> compared to net content, about 290GB). See other post "inefficient bytea
> escaping" for details.

The conventional wisdom is that pg_dump files are substantially smaller
than the on-disk footprint ... and that's even without compressing them.
I think you are taking a corner case, ie bytea data, and presenting it
as something that ought to be the design center.

Something that might be worth considering is an option to allow pg_dump
to use binary COPY. I don't think this'd work nicely for text dumps,
but seems like custom- or tar-format dumps could be made to use it.
This would probably be a win for many datatypes not only bytea, and it'd
still be far more portable than a filesystem dump.

regards, tom lane

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