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Re: [HACKERS] Online backup vs Continuous backup

From: Greg Stark <gsstark(at)mit(dot)edu>
To: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, PostgreSQL-documentation <pgsql-docs(at)postgresql(dot)org>
Subject: Re: [HACKERS] Online backup vs Continuous backup
Date: 2005-12-27 18:59:41
Message-ID: 87mzim5psy.fsf@stark.xeocode.com (view raw or flat)
Thread:
Lists: pgsql-docspgsql-hackerspgsql-patches
Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:

> I noticed that we are using the term "Online Backup" in our
> documentation when we are talking about continuous backup and PITR.
> 
> To me, "online backup" is doing a backup while the system is online
> (online-backup), and that is accomplished by pg_dump.  

Well fwiw what pg_dump does isn't even considered a "backup" at all in other
systems. It's a "logical export" or something of that sort. 

It's not considered a "backup" because it's saving something different than
the actual physical database. When you restore you get something (hopefully)
logically equivalent but still physically different.

Hot backups which is what you read "online backup" to mean is pretty closely
tied to PITR log archiving backups. One isn't very useful without the other.
Specifically, you can have all the archived logs in the world but if you don't
have a backup to start from they're useless. And in postgres I gather hot
backups aren't very useful if you don't have the transaction logs necessary to
fix any torn pages.


-- 
greg


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