Re: pgsql: Add new replication mode synchronous_commit = 'remote_apply'.

On Wed, Mar 30, 2016 at 10:31 AM, Robert Haas <rhaas@postgresql.org> wrote:
> Add new replication mode synchronous_commit = 'remote_apply'.
>
> In this mode, the master waits for the transaction to be applied on
> the remote side, not just written to disk.  That means that you can
> count on a transaction started on the standby to see all commits
> previously acknowledged by the master.
>
> To make this work, the standby sends a reply after replaying each
> commit record generated with synchronous_commit >= 'remote_apply'.
> This introduces a small inefficiency: the extra replies will be sent
> even by standbys that aren't the current synchronous standby.  But
> previously-existing synchronous_commit levels make no attempt at all
> to optimize which replies are sent based on what the primary cares
> about, so this is no worse, and at least avoids any extra replies for
> people not using the feature at all.
>
> Thomas Munro, reviewed by Michael Paquier and by me.  Some additional
> tweaks by me.

The commit message does not directly mention that the spec of
walrcv_receive has been changed in a backward-incompatible way so as
the wait control can be done with a latch directly in walreceiver.c
and not in libpqwalreceiver.c. That's not worth a mention in the
release notes as this is really low-level and compilation on any code
using this hook would simply fail on 9.6, so I am just mentioning it
for the sake of the archives.
--
Michael