Re: Streaming a base backup from master

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Stephen Frost" <sfrost(at)snowman(dot)net>
Cc: "Heikki Linnakangas" <heikki(dot)linnakangas(at)enterprisedb(dot)com>, "Robert Haas" <robertmhaas(at)gmail(dot)com>, "Magnus Hagander" <magnus(at)hagander(dot)net>, "Dave Page" <dpage(at)pgadmin(dot)org>, "PostgreSQL-development" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Streaming a base backup from master
Date: 2010-09-03 15:32:20
Message-ID: 4C80CEB40200002500035182@gw.wicourts.gov
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>Stephen Frost <sfrost(at)snowman(dot)net> wrote:

> We have something much better, called WAL. If people want to keep
> their backup current, they should use that after getting the base
> backup up and working.

Unless you want to provide support for Point In Time Recovery
without excessive recovery times.

> We don't need to support this for the base backup, imv.

We found that making a hard-link copy of the previous base backup
and using rsync to bring it up to date used 1% the WAN bandwidth as
sending a complete, compressed base backup. Just sending modified
files in their entirety would have bought the first order of
magnitude; recognizing the unchanged portions buys the second order
of magnitude.

> In any case, it's certainly not something required for an initial
> implementation..

No disagreement there; but sometimes it pays to know where you might
want to go, so you don't do something to make further development in
that direction unnecessarily difficult.

-Kevin

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