Horton

Re: Standalone synchronous master

Florian G. Pflug <fgp@phlo.org>

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From: Florian Pflug <fgp@phlo.org>
To: Josh Berkus <josh@agliodbs.com>
Cc: Heikki Linnakangas <hlinnakangas@vmware.com>, Rajeev rastogi <rajeev.rastogi@huawei.com>, "Joshua D. Drake" <jd@commandprompt.com>, Jim Nasby <jim@nasby.net>, Hannu Krosing <hannu@2ndQuadrant.com>, Bruce Momjian <bruce@momjian.us>, Andres Freund <andres@2ndquadrant.com>, Amit Kapila <amit.kapila16@gmail.com>, MauMau <maumau307@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Kevin Grittner <kgrittn@ymail.com>, Simon Riggs <simon@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2014-01-24T22:25:19Z
Lists: pgsql-hackers 
On Jan24, 2014, at 22:29 , Josh Berkus <josh@agliodbs.com> wrote:
> On 01/24/2014 12:47 PM, Heikki Linnakangas wrote:
>> ISTM the consensus is that we need better monitoring/administration
>> interfaces so that people can script the behavior they want in external
>> tools. Also, a new synchronous apply replication mode would be handy,
>> but that'd be a whole different patch. We don't have a patch on the
>> table that we could consider committing any time soon, so I'm going to
>> mark this as rejected in the commitfest app.
> 
> I don't feel that "we'll never do auto-degrade" is determinative;
> several hackers were for auto-degrade, and they have a good use-case
> argument.  However, we do have consensus that we need more scaffolding
> than this patch supplies in order to make auto-degrade *safe*.
> 
> I encourage the submitter to resumbit and improved version of this patch
> (one with more monitorability) for  9.5 CF1.  That'll give us a whole
> dev cycle to argue about it.

There seemed to be at least some support for having way to manually
degrade from sync rep to async rep via something like

  ALTER SYSTEM SET synchronous_commit='local';

Doing that seems unlikely to meet much resistant on grounds of principle,
so it seems to me that working on that would be the best way forward for
the submitter. I don't know how hard it would be to pull this off,
though.

best regards,
Florian Pflug