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Re: Re: [COMMITTERS] pgsql: Efficient transaction-controlled synchronous replication.

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Simon Riggs <simon(at)2ndQuadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Re: [COMMITTERS] pgsql: Efficient transaction-controlled synchronous replication.
Date: 2011-03-07 13:30:34
Message-ID: 4D74DDFA.70800@dunslane.net (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers

On 03/07/2011 02:29 AM, Heikki Linnakangas wrote:
> On 07.03.2011 01:28, Simon Riggs wrote:
>> On Sun, 2011-03-06 at 18:09 -0500, Andrew Dunstan wrote:
>>>
>>> On 03/06/2011 05:51 PM, Simon Riggs wrote:
>>>> Efficient transaction-controlled synchronous replication.
>>>
>>> I'm glad this is in, but I thought we agreed NOT to call it 
>>> "synchronous
>>> replication".
>>
>> The discussion on the thread was that its not sync rep unless we have
>> the strictest guarantees. We have the strictest guarantees, so it
>> qualifies as sync rep.
>
> What do you mean by "strictes guarantees"?
>
> I don't see allow_synchronous_standby setting in the committed patch. 
> I presume you didn't make allow_synchronous_standby=off the default 
> behavior. Also, the documentation that describes this as two-safe 
> replication and claims that "the only possibility that data can be 
> lost is if both the primary and the standby suffer crashes at the same 
> time" needs big fat caveats to clarify that this doesn't actually 
> achieve those guarantees.
>
> Please change the name.
>

Previously, Simon said:

> Truly "synchronous" requires two-phase commit, which this never was.

So I too am confused about how it's now become "truly synchronous". Are 
we saying this give the same or better guarantees than a 2PC setup?

cheers

andrew


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