confirmed_flush_lsn shows LSN of the data that has not yet been received by the logical subscriber.

Hi All,

The logically decoded data are sent to the logical subscriber at the time
of transaction commit, assuming that the data is small. However, before the
transaction commit is performed, the LSN representing the data that is yet
to be received by the logical subscriber appears in the confirmed_flush_lsn
column of pg_replication_slots catalog. Isn't the information seen in the
confirmed_flush_lsn column while the transaction is in progress incorrect ?
esp considering the description given in the pg doc for this column.

Actually, while the transaction is running, the publisher keeps on sending
keepalive messages containing LSN of the last decoded data saved in reorder
buffer and the subscriber responds with the same LSN as the last received
LSN which is then updated as confirmed_flush_lsn by the publisher. I think
the LSN that we are sending with the keepalive message should be the one
representing the transaction begin message, not the LSN of the last decoded
data which is yet to be sent. Please let me know if I am missing something
here.

--
With Regards,
Ashutosh Sharma.