Horton

Re: Standalone synchronous master

Joshua D. Drake <jd@commandprompt.com>

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From: "Joshua D. Drake" <jd@commandprompt.com>
To: Hannu Krosing <hannu@2ndQuadrant.com>, Florian Pflug <fgp@phlo.org>, Josh Berkus <josh@agliodbs.com>
Cc: 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>, Heikki Linnakangas <hlinnakangas@vmware.com>, Simon Riggs <simon@2ndquadrant.com>, Rajeev rastogi <rajeev.rastogi@huawei.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2014-01-13T18:21:47Z
Lists: pgsql-hackers 
On 01/13/2014 10:12 AM, Hannu Krosing wrote:
>>> 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.
>>
>
> ++1

+1

>
> I like Simons idea to have a pg_xxx function for switching between
> replication modes, which should be enough to support a monitor
> daemon doing the switching.
>
> Maybe we could have an 'syncrep_taking_too_long_command' GUC
> which could be used to alert such a monitoring daemon, so it can
> immediately check weather to
>

I would think that would be a column in pg_stat_replication. Basically 
last_ack or something like that.


> a) switch master to async rep or standalone mode (in case of sync slave
> becoming unavailable)

Yep.

>
> or
>
> b) to failover to slave (in almost equally likely case that it was the
> master
> which became disconnected from the world and slave is available)
>
> or

I think this should be left to external tools.

JD


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