When we take the snapshot of running transactions in the master, in
GetRunningTransactionData(), it only includes top-level xids and those
subxids that are in the subxid caches. Overflowed subxids are not
included. Isn't that a problem? When the standby initializes the
recovery procs using the running xacts information, pg_subtrans doesn't
isn't set for the overflowed xids, because that information is not
included in the WAL record. If you're lucky, the information is there
already, but we don't generally guarantee pg_subtrans to survive crash
or restart.
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com