Re: Disallow quorum uncommitted (with synchronous standbys) txns in logical replication subscribers

On 1/6/22, 11:25 PM, "Jeff Davis" <pgsql(at)j-davis(dot)com> wrote:
> On Wed, 2022-01-05 at 23:59 -0800, SATYANARAYANA NARLAPURAM wrote:
>> I would like to propose a GUC send_Wal_after_quorum_committed which
>> when set to ON, walsenders corresponds to async standbys and logical
>> replication workers wait until the LSN is quorum committed on the
>> primary before sending it to the standby. This not only simplifies
>> the post failover steps but avoids unnecessary downtime for the async
>> replicas. Thoughts?
>
> Do we need a GUC? Or should we just always require that sync rep is
> satisfied before sending to async replicas?
>
> It feels like the sync quorum should always be ahead of the async
> replicas. Unless I'm missing a use case, or there is some kind of
> performance gotcha.

I don't have a strong opinion on whether there needs to be a GUC, but
+1 for the ability to enforce sync quorum before sending WAL to async
standbys. I think that would be a reasonable default behavior.

Nathan