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Re: Hot Standby query cancellation and Streaming Replication integration

From: Greg Smith <greg(at)2ndquadrant(dot)com>
To: Aidan Van Dyk <aidan(at)highrise(dot)ca>
Cc: Greg Stark <gsstark(at)mit(dot)edu>, 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 05:08:35
Message-ID: 4B88A8D3.2070406@2ndquadrant.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Aidan Van Dyk wrote:
> Would we (ya, the royal we) be willing to say that if you want the
> benifit of removing the MVCC overhead of long-running queries you need
> to run PITR backup/archive recovery, and if you want SR, you get a
> closed-loop master-follows-save-xmin behaviour?
>   

To turn that question around a little, I think it's reasonable to say 
that closed-loop master-follows-slave-xmin behavior is only practical to 
consider implementing with SR--and even there, it should be optional 
rather than required until there's more field experience on the whole 
thing.  Whether it's the default or not could take a bit of debate to 
sort out too.

If you think of it in those terms, the idea that "you need to run PITR 
backup/archive recovery" to not get that behavior isn't an important 
distinction anymore.  If you run SR with the option enabled you could 
get it, any other setup and you won't.

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


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