Re: Inconsistent error handling in START_REPLICATION command

On Wed, Jan 20, 2016 at 2:28 AM, Craig Ringer <craig@2ndquadrant.com> wrote:
> It enters COPY BOTH mode before it invokes the startup callback. The client
> has no way to unilaterally terminate COPY BOTH mode and return to the normal
> walsender protocol. The server doesn't do it when there's an ERROR. So the
> only option the client has for recovery is to disconnect and reconnect.

This isn't my understanding of how the protocol works, and it's not
what the documentation says either.

Per http://www.postgresql.org/docs/current/static/protocol-flow.html:

===
In the event of a backend-detected error during copy-both mode, the
backend will issue an ErrorResponse message, discard frontend messages
until a Sync message is received, and then issue ReadyForQuery and
return to normal processing. The frontend should treat receipt of
ErrorResponse as terminating the copy in both directions; no CopyDone
should be sent in this case.
===

So it's true that the client can't unilaterally terminate COPY BOTH
mode; it can only send CopyDone.  But an error on the server side
should do so.