Message-ID: <4C386B33.8090708@2ndquadrant.com>
Date: Sat, 10 Jul 2010 13:44:35 +0100
From: Greg Smith <greg@2ndquadrant.com>
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To: Thomas Kellerer <spam_eater@gmx.net>
CC: pgsql-admin@postgresql.org
Subject: Re: High Availability: Hot Standby vs. Warm Standby
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Thomas Kellerer wrote:
> I'm wondering about the differences when the failover situation 
> occurs. From reading the docs, I get the impression that 9.0's 
> streaming replication might be faster than 8.4's WAL shipping, but 
> otherwise offers the same level of data protection.
> Is there a difference in how much data could potentially be lost in 
> case of a failover?
> E.g. because 9.0 replicates the changes quicker than 8.4?

There's nothing that 9.0 does that you can' t do with 8.4 and the right 
software to aggressively ship partial files around.  In practice though, 
streaming shipping is likely to result in less average data loss simply 
because it will do the right thing to ship new transactions 
automatically.  Getting the same reaction time and resulting low amount 
of lag out of an earlier version requires a level of external script 
configuration that few sites every actually manage to obtain.  You can 
think of the 9.0 features as mainly reducing the complexity of 
installation needed to achieve low latency significantly.  I would bet 
that if you tried to setup 8.4 to achieve the same quality level in 
terms of quick replication, your result would be more fragile and buggy 
than just using 9.0--the bugs would be just be in your own code rather 
than in the core server.

-- 
Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com   www.2ndQuadrant.us