Re: Retrieve the snapshot's LSN

On Fri, Jul 17, 2015 at 8:31 AM, Florent Guiliani <florent(at)guiliani(dot)fr> wrote:
> A pg_export_snapshot_for_slot(...) would work very well.
>
> Let me explain the use case. You have many downstream systems that are
> replicated with logical decoding. Using a dedicated replication slot
> for each target is not practical. A single logical replication slot is
> configured. It generates a stream of LSN-stamped transactions in
> commit order. Those transactions are published to all downstream
> nodes.
>
> The snapshot exported during the slot creation can be used to generate
> a complete dump that the replicated systems will load before applying
> the transaction stream.
>
> How do you individually reload/recover one of the downstream node? You
> can use the initial dump and reapply all transactions emitted since
> the slot's inception. It will quickly become impractical. What you
> need is to generate a newer dump and only apply the transactions from
> that point.

I'd like to point out that I told Andres repeatedly during the
development of logical decoding that this exact thing was going to be
a problem. He told me fixing it was way too complicated, but I hope
he'll relent, because I still think this is important.

(Not trying to be a jerk here.)

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company