Horton

Re: Standalone synchronous master

Bruce Momjian <bruce@momjian.us>

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From: Bruce Momjian <bruce@momjian.us>
To: Josh Berkus <josh@agliodbs.com>
Cc: Andres Freund <andres@2ndquadrant.com>, "Joshua D. Drake" <jd@commandprompt.com>, Amit Kapila <amit.kapila16@gmail.com>, Hannu Krosing <hannu@2ndquadrant.com>, MauMau <maumau307@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Kevin Grittner <kgrittn@ymail.com>, Heikki Linnakangas <hlinnakangas@vmware.com>, Simon Riggs <simon@2ndquadrant.com>, Rajeev rastogi <rajeev.rastogi@huawei.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2014-01-11T02:27:37Z
Lists: pgsql-hackers 
On Fri, Jan 10, 2014 at 03:27:10PM -0800, Josh Berkus wrote:
> On 01/10/2014 01:49 PM, Andres Freund wrote:
> > On 2014-01-10 10:59:23 -0800, Joshua D. Drake wrote:
> >>
> >> On 01/10/2014 07:47 AM, Bruce Momjian wrote:
> >>
> >>> I know there was a desire to remove this TODO item, but I think we have
> >>> brought up enough new issues that we can keep it to see if we can come
> >>> up with a solution.  I have added a link to this discussion on the TODO
> >>> item.
> >>>
> >>> I think we will need at least four new GUC variables:
> >>>
> >>> *  timeout control for degraded mode
> >>> *  command to run during switch to degraded mode
> >>> *  command to run during switch from degraded mode
> >>> *  read-only variable to report degraded mode
> 
> I would argue that we don't need the first.  We just want a command to
> switch synchronous/degraded, and a variable (or function) to report on
> degraded mode.  If we have those things, then it becomes completely
> possible to have an external monitoring framework, which is capable of
> answering questions like "is the replica down or just slow?", control
> degrade.
> 
> Oh, wait!  We DO have such a command.  It's called ALTER SYSTEM SET!
> Recently committed.  So this is really a solvable issue if one is
> willing to use an external utility.

How would that work?  Would it be a tool in contrib?  There already is a
timeout, so if a tool checked more frequently than the timeout, it
should work.  The durable notification of the admin would happen in the
tool, right?

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + Everyone has their own god. +