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Re: Differential Backups

From: Alvaro Herrera <alvherre(at)atentus(dot)com>
To: Doug McNaught <doug(at)wireboard(dot)com>
Cc: Ian Harding <ianh(at)tpchd(dot)org>, <pgsql-general(at)postgresql(dot)org>
Subject: Re: Differential Backups
Date: 2001-10-30 02:07:24
Message-ID: Pine.LNX.4.33L2.0110292302210.15563-100000@aguila.protecne.cl (view raw or flat)
Thread:
Lists: pgsql-general
On 29 Oct 2001, Doug McNaught wrote:

> "Ian Harding" <ianh(at)tpchd(dot)org> writes:
>
> > I have been thinking about backups.  I currently do one a day.
> > However, I thought it might be nice to get differential backups
> > through the day.

> Interesting idea.  The one thing I might worry about is that 'diff'
> might (I'm not familiar with its algorithm) eat a great deal of memory
> if the dumps you're comparing are very large and significantly
> different.

GNU diff reads in memory both files. You sure need lots to compare
medium sized databases, and I don't think this method will work on big
ones.

I think this has to be implemented inside the database; maybe there's a
way of extracting the data from WAL logs (committed transactions?). Then
you need to go to the tables and see what each transaction did...

Another way to do it could be to store a timestamp on each tuple, and
check that for the diff backup. Sounds like you're going to enlarge your
data a lot by just having the timestamps...

-- 
Alvaro Herrera (<alvherre[(at)]atentus(dot)com>)
"Coge la flor que hoy nace alegre, ufana. QuiƩn sabe si nacera otra man~ana?"


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