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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: Aidan Van Dyk <aidan(at)highrise(dot)ca>, 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 15:51:49
Message-ID: 4D74FF15.1070804@dunslane.net (view raw or flat)
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Lists: pgsql-committerspgsql-hackers

On 03/07/2011 10:46 AM, Heikki Linnakangas wrote:
> On 07.03.2011 17:03, Andrew Dunstan wrote:
>> This is about expectations. The thing that worries me is that the use of
>> this term might cause some people NOT to use 2PC because they think they
>> are getting an equivalent guarantee, when in fact they are not. And
>> that's hardly unreasonable. Here for example is what wikipedia says
>> <http://en.wikipedia.org/wiki/Replication_%28computer_science%29>:
>>
>> Synchronous replication - guarantees "zero data loss" by the means
>> of atomic write operation, i.e. write either completes on both sides
>> or not at all. Write is not considered complete until
>> acknowledgement by both local and remote storage.
>
> Hmm, I've read that wikipedia definition before, but the "atomic" part 
> never caught my eye. You do get zero data loss with what we have; if a 
> meteor strikes the master, no acknowledged transaction is lost. I find 
> that definition a bit confusing.

Maybe it is - I agree the difference might be small. I'm just trying to 
make sure we don't use a term that could mislead reasonable people about 
what we're providing. If we're satisfied that we aren't, then keep it.

cheers

andrew

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