There is a bug in hot_standby_feedback that causes the xmin of the
walsender process to not be reset when hot_standby_feedback is turned
off after it had previously sent at least one feedback message.
Clearly, that is a bad thing and deserves backpatching to 9.1, unless
I hear otherwise real soon.
Attached patch sends an immediate feedback message if it is turned off
on the standby. No protocol changes, just changes to how message is
handled and when it is sent.
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Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services