Re: pgsql: Fix a couple of bugs in MultiXactId freezing

Magnus Hagander <magnus@hagander.net> writes:
> On Tue, Dec 3, 2013 at 7:20 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

>> I assume what would happen is the slave would PANIC upon seeing a WAL
>> record code it didn't recognize.

> I wonder if we should for the future have the START_REPLICATION command (or
> the IDENTIFY_SYSTEM would probably make more sense - or even adding a new
> command like IDENTIFY_CLIENT. The point is, something in the replication
> protocol) have walreceiver include it's version sent to the master. That
> way we could have the walsender identify a walreceiver that's too old and
> disconnect it right away - with a much  nicer error message than a PANIC.

Meh.  That only helps for the case of streaming replication, and not for
the thirty-seven other ways that some WAL might arrive at something that
wants to replay it.

It might be worth doing anyway, but I can't get excited about it for this
scenario.