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Re: Sync Rep Design

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Sync Rep Design
Date: 2011-01-01 16:55:57
Message-ID: 1293900957.1892.60412.camel@ebony (view raw or flat)
Thread:
Lists: pgsql-hackers
On Sat, 2011-01-01 at 16:12 +0100, Stefan Kaltenbrunner wrote:

> I still would like to get a statement on why simon thinks that 
> the design heikki and others have proposed 

I've explained in huge detail why I think what I think, nor avoided any
technical issue.

It appears to me there has been substantial confusion over alternatives,
because of a misunderstanding about how synchronisation works. Requiring
confirmation that standbys are in sync is *not* the same thing as them
actually being in sync. Every single proposal made by anybody here on
hackers that supports multiple standby servers suffers from the same
issue: when the primary crashes you need to work out which standby
server is ahead.


> - The docs should not allege that either setup is preferable to the
> > other, because there is not now and will never be consensus that this
> > is in fact true.

I remain hopeful that people will read what I have read and understand
it. Having taken the trouble to do that publicly, my conscious is clear
that I've done the very best to explain things and make it easy for
users to avoid error. If I am prevented from putting sound advice into
the docs, I'll not worry too much.


> well I should think we need to clearly spell out everything that affects 
> reliability and if we only support semi-sync for more than 1 standby we 
> have only that setup :)

You can use sync rep with 1 or more standby servers.

At the end of the day, I can't stop anyone from saying "What an idiot,
he designed something that gave the same durability and availability as
Oracle and MySQL do, yet with additional performance management
features".

-- 
 Simon Riggs           http://www.2ndQuadrant.com/books/
 PostgreSQL Development, 24x7 Support, Training and Services
 


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