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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: AANLkTinrSO0r7ZiNRaNV4jtKpAyjSB5nmZZwZsdEPK6x@mail.gmail.com (view raw or flat)
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.

Regards,

-- 
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center

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Subject: quorum commit Re: Synchronous replication
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