Postgres sends these messages, and then based on the reply discards the wal up to that position.

As a developer I should be able to have my event handler update this wal position such that Postgres doesn't discard the wal until I know my work is done.

• eg I should be able to write to S3 and then on successful write, make a call to update the latest successful position I have internally.
• Then this keepalive handler should call for the latest successful position and report that back to Postgres.