To: pgsql-admin@postgresql.org
From: Thomas Kellerer <spam_eater@gmx.net>
Subject: Re: High Availability: Hot Standby vs. Warm Standby
Date: Mon, 12 Jul 2010 08:58:58 +0200
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Greg Smith, 10.07.2010 14:44:
>> 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 and Rob,

thanks for the answers.

I didn't "plan" (or expect) to get the same level of reliability from a "standard" 8.4 HA installation, so I don't think I would go that way. If we do need that level, we'd go for 9.0 or for some other solution.

The manual lists three possible solutions to HA: shared disk failover, file system replication and Warm/Hot Standby. I'm not an admin (nor a DBA), so my question might sound a bit stupid: from my point of view solutions using shared disk failover of file system replication seem to be more reliable in terms of how much data can get lost (and possibly the switch over lag)

Regards
Thomas