Re: Synchronous Replication Timeout

On Fri, Nov 28, 2014 at 10:24 AM, Teresa Bradbury <TB(at)quintessencelabs(dot)com>
wrote:

> I have a replication setup with a master and a single synchronous slave.
> If the slave dies (or the network goes down) I would like any transaction
> on the master that requires writing to fail so I can roll it back. At the
> moment, when I commit it just hangs forever or (if I cancel it using ^C in
> psql or using kill) it commits locally and not on the synchronous slave.
>

​I did that for a customer and I am using a tool (pgpool) to change the
config file if the master is going down. You can keep additional
configurations in
synchronous_master.conf and add include header in postgresql.conf

You just need to write a shell script (or use something like pgpool)​ to
keep a watch if the slave goes down change synchronous_master.conf to an
empty file and reload the postgres config (pg_ctl reload).

> Neither of these options are ok in my use case. I have tried setting
> statement_timeout but it does not work. So my questions are:
>
>
>
> 1) Is it possible to rollback transactions that fail to commit after a
> certain amount of time waiting for the slave?
>

​No, AFAIK it would have already committed to WAL files on on master.​

​It is just blocked till the slave confirms the ​same being done at its end.

>
> 2) If not, is there any intension of implementing such a feature in the
> near future?
>
>
>
> 3) Do any of the answers above change if we are dealing with two-phase
> commits instead? At the moment it hangs forever on ‘prepare transaction’,
> ‘commit prepared’ and ‘rollback prepared’ commands.
>
>

Best Regards,

*Sameer Kumar | Database Consultant*

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