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From "Peter Crowther" <>
Subject [OT] Replication (was RE: Copying large files around)
Date Mon, 15 Oct 2007 09:38:57 GMT
[Marked off-topic as this has, indeed, come a long long way from the
original question]

> From: Johnny Kewl [] 
> but yes if the user could consider replication 
> and the required
> dB design, much better than moving GB files around.

Not always.  For example, replication has the disadvantage that an
application logic error can get replicated and break both your live and
your backup database (although I accept that point-in-time log-based
recovery can mitigate this).  Point-in-time backups that are copied
between machines have a long and honourable history; they're also often
much easier for the ops team to get their heads round, where a
replicated system can often set heads spinning in the ops team.  You
also have to be very careful with your replication setup - and the
guarantees you give your client - in case of partial failures.  For
example, if commuinications to the second system fails, do you stop
accepting transactions on the primary (potential loss of new business on
an Internet site) or do you continue, but in the knowledge that if the
primary fails you're now losing transactions and hence violating ACID
principles from the client's point of view (potential loss of old
business on an Internet site)?

(As you can probably guess, I've designed and built my share of
replicated databases - and supported them!)

		- Peter

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