An earlier comment from Anders:
> We could e.g. have a new LogicalDecodingContext callback that is
> called whenever WalSndWaitForWal() would wait. That'd check if there's
> a pending "need" to send out a 'empty transaction'/feedback request
> message. The "need" flag would get cleared whenever we send out data
> bearing an LSN for other reasons.
>
I think the current Keep Alive messages already achieve this by
sending the current LSN as part of the Keep Alive messages.
/* construct the message... */
resetStringInfo(&output_message);
pq_sendbyte(&output_message, 'k');
pq_sendint64(&output_message, sentPtr); <=== Last sent WAL LSN
pq_sendint64(&output_message, GetCurrentTimestamp());
pq_sendbyte(&output_message, requestReply ? 1 : 0);
I'm not sure if anything more is required to keep empty transactions
updated as part of synchronous replicas. If my understanding on this
is not correct, let me know.
regards,
Ajin Cherian
Fujitsu Australia