Re: High Availability: Hot Standby vs. Warm Standby

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(at)2ndQuadrant(dot)com www.2ndQuadrant.us