Hi,
While reading logical replication code, I found an issue in LogicalConfirmReceivedLocation().
In LogicalConfirmReceivedLocation(), updated_restart is tracked independently from updated_xmin, and the slot is marked
dirtyand saved when either one changed. But after that, ReplicationSlotsComputeRequiredLSN() is still only called
inside"if (updated_xmin)”.
So for the restart-only case:
* updated_restart = true
* updated_xmin = false
* ReplicationSlotSave() runs
* ReplicationSlotsComputeRequiredLSN() does not run because updated_xmin is false
That means the global retention point managed by XLogSetReplicationSlotMinimumLSN() can stay stale until some later
unrelatedevent recomputes it. Since ReplicationSlotsComputeRequiredLSN() derives the global minimum from slot
restat_lsn,skipping it after a restart-only advance can retain excess WAL and may lead to WAL bloat.
This patch fixes the problem by moving ReplicationSlotsComputeRequiredLSN() under “if (updated_restart)”.
Looks like this issue has been there for a long time, so if this analysis is correct, it may also be worth
back-patching.
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
