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Re: Sync Rep Design

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Sync Rep Design
Date: 2010-12-30 21:47:42
Message-ID: AANLkTi=rGTp59iB5Qpf0ymwzn31F0oVOVuVCR_TAMPi5@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, Dec 30, 2010 at 3:42 PM, Stefan Kaltenbrunner
<stefan(at)kaltenbrunner(dot)cc> wrote:
>> synchronous replication for high performance applications. This feature
>> is unique to PostgreSQL.
>
> that seems to be a bit too much marketing for a reference level document

+1.

> It also does not address the more general (not sync rep specific) problem of
> how to deal with max_keep_segments which is a wart and I was hoping we could
> get rid of in 9.1 - but it would require a real standby registration or at
> least standby management possibility on the master not a halfway done one -
> so do we really need hot_standby_feedback as part of the inital sync-rep
> patch?

And this is really the key point on which previous discussions of sync
rep stalled.  Simon is clearly of the opinion that any system where
the slaves have an individual identities (aka "standby registration")
is a bad idea, but the only justification he's offered for that
position is the assertion that it doesn't allow any added
functionality.  As you point out, and as has been pointed out before,
this is not true, but unless Simon has changed his position since the
last time we discussed this, he will not only refuse to include any
kind of standby identifier in any of his proposals, but will also
argue against including any such code even if it is written by someone
else.  I don't understand why, but that's how it is.

Synchronous replication would probably be done and committed by now if
it weren't for this issue.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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