Fix how flush_pos is compared to commit_lsn. #50
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When we logically replicate the message with LSN equal to exactly X, we need to wait for `flush_pos` of other replicas to become strictly greater than X, not greater or equal. Both `restart_lsn` and `confirmed_flush` represent the oldest LSN that must still be kept so it can still be replicated. That means that it might NOT yet be replicated.
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When we logically replicate the message with LSN equal to exactly X, we need to wait for
flush_posof other replicas to become strictly greater than X, not greater or equal.Both
restart_lsnandconfirmed_flushrepresent the oldest LSN that must still be kept so it can still be replicated. That means that it might NOT yet be replicated.--
I made some trivial experiment to check how
pg_failover_slots.standby_slot_namesbehaves and noticed that my logical replica always gets one extra record when the physical replica becomes unavailable. With this fix it works as expected: logical replica is never delayed more then necessary, but no records that were not replicated to physical replica are replicated to the logical one.