Date: Tue, 07 Apr 2009 22:31:02 +1200
From: Mark Kirkwood <markir@paradise.net.nz>
Subject: Re: Best replication solution?
In-reply-to: <20090406123529.GA14675@shinkuro.com>
To: Andrew Sullivan <ajs@crankycanuck.ca>, pgsql-performance@postgresql.org
Message-id: <49DB2B66.1080801@paradise.net.nz>
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	<20090406123529.GA14675@shinkuro.com>
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Andrew Sullivan wrote:
> On Sun, Apr 05, 2009 at 11:36:33AM -0700, Lists wrote:
>
>   
>> *Slony-I* - I've used this in the past, but it's a huge pain to work  
>> with, caused serious performance issues under heavy load due to long  
>> running transactions (may not be the case anymore, it's been a while  
>> since I used it on a large database with many writes), and doesn't seem  
>> very reliable (I've had replication break on me multiple times).
>>     
>
>  
> I'm also somewhat puzzled by the claim of unreliability:
> most of the actual replication failures I've ever seen under Slony are
> due to operator error (these are trivial to induce, alas --
> aforementioned pain to work with again).  Slony is baroque and
> confusing, but it's specifically designed to fail in safe ways (which
> is not true of some of the other systems: several of them have modes
> in which it's possible to have systems out of sync with each other,
> but with no way to detect as much.  IMO, that's much worse, so we
> designed Slony to fail noisily if it was going to fail at all).  
>
>   

 From my experience - gained from unwittingly being in the wrong place 
at the wrong time and so being volunteered into helping people with 
Slony failures - it seems to be quite possible to have nodes out of sync 
and not be entirely aware of it - in addition to there being numerous 
ways to shoot yourself in the foot via operator error. Complexity seems 
to be the major evil here.

I've briefly experimented with Londiste, and it is certainly much 
simpler to administer. Currently it lacks a couple of features Slony has 
(chained slaves and partial DDL support), but I'll be following its 
development closely - because if these can be added - whilst keeping the 
operator overhead (and the foot-gun) small, then this looks like a winner.

regards

Mark