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Re: Sync Rep: First Thoughts on Code

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Cc: Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Sync Rep: First Thoughts on Code
Date: 2008-12-23 15:38:34
Message-ID: 1230046714.4793.858.camel@ebony.2ndQuadrant (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, 2008-12-23 at 23:31 +0900, Fujii Masao wrote:
> Hi,
> 
> On Tue, Dec 23, 2008 at 10:41 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> > I'm happy if that whole feature is added. If we do add it, it will be a
> > utility like "pg_resync". So in admin terms it will be almost identical
> > to using rsync, just a specific version that minimizes effort even more
> > than rsync does currently. The only difference as I see it would be some
> > gain in performance, but we don't need to send the whole database down
> > the wire again in either case.
> 
> I think that the type of your user is different from mine. 

Perhaps, but why do you say that? I've not blocked you from adding
anything useful to Postgres.

> If server fails
> by simple termination of process, I don't want to spend 1min for
> restarting other than catching up itself. For me, getting a fresh backup
> (not only copying backup data but also checkpoint by pg_start_backup)
> is expensive operation.

As I said: "I'm happy if that whole feature is added."

You scare me that you see failover as sufficiently frequent that you are
worried that being without one of the servers for an extra 60 seconds
during a failover is a problem. And then say you're not going to add the
feature after all. I really don't understand. If its important, add the
feature, the whole feature that is. If not, don't.

My expectation is that most failovers are serious ones, that the primary
system is down and not coming back very fast. Your worries seem to come
from a scenario where the primary system is still up but Postgres
bounces/crashes, we can diagnose the cause of the crash, decide the
crashed server is safe and then wish to recommence operations on it
again as quickly as possible, where seconds count it doing so.

Are failovers going to be common? Why?

> Of course, since I'm not planning to tackle that problem in 8.4,

If you change your mind, having it in 8.4 would be good. 

-- 
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support


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