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Re: Core team statement on replication in PostgreSQL

From: Mathias Brossard <mathias(dot)brossard(at)opentrust(dot)com>
To:
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Core team statement on replication in PostgreSQL
Date: 2008-05-29 21:37:44
Message-ID: 483F2228.9060100@opentrust.com (view raw or flat)
Thread:
Lists: pgsql-advocacypgsql-hackers
Peter Eisentraut wrote:
> Mathias Brossard wrote:
>>  From what I gather from those slides it seems to me that the NTT solution
>> is synchronous not asynchronous. In my opinion it's even better, but I do
>> understand that others might prefer asynchronous. I'm going to speculate,
>> but I would think it should be possible (without a substancial rewrite) to
>> support both modes (or even some intermediate modes, like DRBD on Linux).
> 
> Well, we already have asynchronous.  The whole point is adding synchronous.

I don't think the current log shipping solution matches, as Tom puts it, 
the « need for simple, built-in replication » (from a user perspective, 
I wouldn't call it "simple").

I pointed out that the NTT solution is synchronous because Tom said in 
the first part of his email that:

 > In practice, simple asynchronous single-master-multiple-slave
 > replication covers a respectable fraction of use cases, so we have
 > concluded that we should allow such a feature to be included in the
 > core project.

... and yet "the most appropriate base technology for this" is 
synchronous and maybe I should have also pointed out in my previous mail 
is that it doesn't support multiple slaves.

Also, as other have pointed out there are different interpretations of 
"synchronous" depending on wether the WAL data has reached the other end 
of the network connection, a safe disk checkpoint or the slave DB itself.

Sincerely,
-- 
Mathias Brossard

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