On Jan12, 2014, at 04:18 , Josh Berkus <josh@agliodbs.com> wrote:
> Thing is, when we talk about auto-degrade, we need to determine things
> like "Is the replica down or is this just a network blip"? and take
> action according to the user's desired configuration. This is not
> something, realistically, that we can do on a single request. Whereas
> it would be fairly simple for an external monitoring utility to do:
>
> 1. decide replica is offline for the duration (several poll attempts
> have failed)
>
> 2. Send ALTER SYSTEM SET to the master and change/disable the
> synch_replicas.
>
> In other words, if we're going to have auto-degrade, the most
> intelligent place for it is in
> RepMgr/HandyRep/OmniPITR/pgPoolII/whatever. It's also the *easiest*
> place. Anything we do *inside* Postgres is going to have a really,
> really hard time determining when to degrade.
+1
This is also how 2PC works, btw - the database provides the building
blocks, i.e. PREPARE and COMMIT, and leaves it to a transaction manager
to deal with issues that require a whole-cluster perspective.
best regards,
Florian Pflug