Re: Hot Standby query cancellation and Streaming Replication integration

Greg Smith wrote:
> Josh Berkus wrote:
>
> > Now that I think about it, the xmin thing really doesn't seem
> > conceptually difficult. If the slave just opens a 2nd, special query
> > connection back to the master and publishes its oldest xmin there, as
> > far as the master is concerned, it's just another query backend.
> > Could it be that easy?
> >
>
> Something just like that is in fact already suggested as a workaround in
> the Hot Standby manual:
>
> "The first option is to connect to the primary server and keep a query
> active for as long as needed to run queries on the standby. This
> guarantees that a WAL cleanup record is never generated and query
> conflicts do not occur, as described above. This could be done using
> contrib/dblink and pg_sleep(), or via other mechanisms."

I am unclear how you would easily advance the snapshot as each query
completes on the slave.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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