Re: Newly created replication slot may be invalidated by checkpoint

On Fri, Jan 23, 2026 at 7:33 AM Zhijie Hou (Fujitsu)
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> This patch cannot be applied cleanly on backbranches, I can prepare patches for
> those once the main patch is stable.
>

Some comments:
1.
+ /*
+ * Determine the minimum non-removable LSN by comparing the redo pointer
+ * with the minimum slot LSN.
+ */
+ min_safe_lsn = GetRedoRecPtr();
+ slot_min_lsn = XLogGetReplicationSlotMinimumLSN();

Can we expand these comments a bit to state why we need both
RedoRecPtr and slot's minimum LSN?

2.
+# Verify that while syncing a slot to the standby server, if the WAL before the
+# remote restart_lsn is at risk of being removed by a checkpoint, the slot
+# cannot be synced. Otherwise, even if the slot syncing succeeds, it may be
+# immediately invalidated by the checkpoint.
+my $primary = $node;

This comment atop the testcase is not very clear. Because, it is
testing that the slot is synced and is not invalidated. How about:
"Verify that the synchronized slots won't be invalidated immediately
after synchronization in the presence of a concurrent checkpoint."?

3.
+# Increase the log_min_messages setting to DEBUG2 on both the standby and
+# primary to debug test failures, if any.
+my $connstr_1 = $primary->connstr;

Do we need this DEBUG2? I don't think we should add too many DEBUG2
tests as it increases Log volume.

--
With Regards,
Amit Kapila.