Re: Standalone synchronous master

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(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ Everyone has their own god. +