Thread: Query regarding replication slots

Hi All,

I have a very basic question related to replication slots. Why should
the master/primary server maintain the replication slot info like lsn
corresponding to each standby server etc. Instead, why can't each
standby server send the lsn that it needs, and master/primary server
maintain the minimum lsn across all of the standby servers so that the
information could be used for cleanup/removal of WAL segments?

The minimum lsn could as well be streamed to all of the standby
servers while streaming the WAL records, so that the cleanup on the
standby server as well happens as per the minimum lsn. Also, even if
the primary server crashes, any standby server becoming the master is
well aware of the minimum lsn and the WAL records required for all of
the remaining standby servers are intact.

Thanks,
RKN

On Tue, Jan 11, 2022 at 04:48:59PM +0530, RKN Sai Krishna wrote:
> Hi All,
> 
> I have a very basic question related to replication slots. Why should
> the master/primary server maintain the replication slot info like lsn
> corresponding to each standby server etc. Instead, why can't each
> standby server send the lsn that it needs, and master/primary server
> maintain the minimum lsn across all of the standby servers so that the
> information could be used for cleanup/removal of WAL segments?

Because the information is needed even if the standby servers are not
available, and if you only have a global xmin then you can't do much when
removing one of the slots.