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Re: Hot Standby query cancellation and Streaming Replication integration

From: Greg Smith <greg(at)2ndquadrant(dot)com>
To: Greg Stark <gsstark(at)mit(dot)edu>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, Dimitri Fontaine <dfontaine(at)hi-media(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Hot Standby query cancellation and Streaming Replication integration
Date: 2010-02-27 03:11:49
Message-ID: 4B888D75.8030006@2ndquadrant.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Greg Stark wrote:
> Eh? That's not what I meant at all. Actually it's kind of the exact
> opposite of what I meant.
>   

Sorry about that--I think we just hit one of those language usage drift 
bits of confusion.  "Sit in the corner" has a very negative tone to it 
in US English and I interpreted your message badly as a result.  A 
Google search for images using that phrase will quickly show you what I 
mean.

> What I meant was that your description of the "High Availability first
> and foremost" is only one possible use case. Simon in the past
> expressed the same single-minded focus on that use case. It's a
> perfectly valid use case and I would probably agree if we had to
> choose just one it would be the most important.
>   

Sure, there are certainly others, and as much as possible more 
flexibility here is a good thing.  What I was suggesting is that if the 
only good way to handle long-running queries has no choice but to 
sacrifice high-availability, which is is the situation if 
max_standby_delay is the approach you use, then the most obvious users 
for this feature are not being well served by that situation.  I would 
guess a large portion of the users looking forward to Hot Standby are in 
the "have an underutilized high-availability standby I'd like to use for 
offloading long running reports", and if there is no way to serve them 
well this feature is missing the mark a bit. 

You really can't do any better without better master/standby integration 
though, and as pointed out a couple of times here that was considered 
and just not followed through on yet.  I'm increasingly concerned that 
nothing else will really do though.

-- 
Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com   www.2ndQuadrant.us


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