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Re: Synchronous replication

From: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
To: Yeb Havinga <yebhavinga(at)gmail(dot)com>
Cc: Aidan Van Dyk <aidan(at)highrise(dot)ca>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Boszormenyi Zoltan <zb(at)cybertec(dot)at>
Subject: Re: Synchronous replication
Date: 2010-07-26 08:41:49
Message-ID: (view raw or whole thread)
Lists: pgsql-hackers
On Mon, Jul 26, 2010 at 5:27 PM, Yeb Havinga <yebhavinga(at)gmail(dot)com> wrote:
> Fujii Masao wrote:
>>> Intuitively by looking at the enumeration of replication_mode I'd think
>>> that
>>> the sync standbys are all standby's that operate in a not async mode.
>>> That
>>> would be clearer with a boolean sync (or not) and for sync standbys the
>>> replication_mode specified.
>> You mean that something like synchronous_replication as the recovery.conf
>> parameter should be added in addition to replication_mode? Since
>> increasing
>> the number of similar parameters would confuse users, I don't like do
>> that.
> I think what would be confusing if there is a mismatch between implemented
> concepts and parameters.
> 1 does the master wait for standby servers on commit?
> 2 how many acknowledgements must the master receive before it can continue?
> 3 is a standby server a synchronous one, i.e. does it acknowledge a commit?
> 4 when do standby servers acknowledge a commit?
> 5 does it only wait when the standby's are connected, or also when they are
> not connected?
> 6..?
> When trying to match parameter names for the concepts above:
> 1 - does not exist, but can be answered with quorum_standbys = 0
> 2 - quorum_standbys
> 3 - yes, if replication_mode != async (here is were I thought I had to think
> to much)
> 4 - replication modes recv, fsync and replay bot not async
> 5 - Zoltan's strict_sync_replication parameter
> Just an idea, what about
> for 4: acknowledge_commit = {no|recv|fsync|replay}
> then 3 = yes, if acknowledge_commit != no

Thanks for the clarification.

I still like

    replication_mode = {async|recv|fsync|replay}

rather than

    synchronous_replication = {on|off}
    acknowledge_commit = {no|recv|fsync|replay}

because the former is more intuitive for me and I don't want
to increase the number of parameters.

We need to hear from some users in this respect. If most want
the latter, of course, I'd love to adopt it.


Fujii Masao
NTT Open Source Software Center

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