Correct logical decoding status at end of recovery with minimal WAL level.

Crash recovery running with wal_level='minimal' can replay an
XLOG_LOGICAL_DECODING_STATUS_CHANGE record that activates logical
decoding, if the server previously ran with a higher wal_level and
crashed after the last logical slot was dropped but before the
checkpointer deactivated logical decoding. Replaying such a record is
correct since it reflects the status at the time it was
written. However, UpdateLogicalDecodingStatusEndOfRecovery() asserted
that logical decoding is never active with wal_level='minimal',
causing an assertion failure at the end of recovery. In production
builds, logical decoding would remain active while running with
wal_level='minimal'.

Instead of special-casing wal_level='minimal', recompute the status at
the end of recovery as usual: no logical slot can exist with
wal_level='minimal' as RestoreSlotFromDisk() would have rejected it,
so the recomputation always deactivates logical decoding in this case,
also writing the corresponding status change record.

Oversight in 67c20979ce7.

Reviewed-by: Guoqing Yang <yanggq1988@126.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Discussion: https://postgr.es/m/CAD21AoAnPAugUnDic+ESvrfXjXHk2bss9eHAD7zP0-Chy2UabA@mail.gmail.com
Backpatch-through: 19

diff --git a/src/backend/replication/logical/logicalctl.c b/src/backend/replication/logical/logicalctl.c
index c11d131645085ed72838c6a896e6ceeb1bd20e4c..624965ef95dce0af037dd2021e23847a29098ea0 100644 (file)
--- a/src/backend/replication/logical/logicalctl.c
+++ b/src/backend/replication/logical/logicalctl.c
@@ -561,19 +561,17 @@ UpdateLogicalDecodingStatusEndOfRecovery(void)
 
        Assert(RecoveryInProgress());
 
-       /*
-        * With 'minimal' WAL level, there are no logical replication slots during
-        * recovery. Logical decoding is always disabled, so there is no need to
-        * synchronize XLogLogicalInfo.
-        */
-       if (wal_level == WAL_LEVEL_MINIMAL)
-       {
-               Assert(!IsXLogLogicalInfoEnabled() && !IsLogicalDecodingEnabled());
-               return;
-       }
-
        LWLockAcquire(LogicalDecodingControlLock, LW_EXCLUSIVE);
 
+       /*
+        * With 'minimal' WAL level, no logical replication slot can exist (see
+        * RestoreSlotFromDisk()), so the new status is always false. However,
+        * logical decoding could have been enabled during recovery by replaying
+        * an XLOG_LOGICAL_DECODING_STATUS_CHANGE record from WAL generated with a
+        * higher wal_level, e.g. if the server crashed right after the last
+        * logical slot was dropped and then restarted with wal_level='minimal'.
+        * The code below disables logical decoding in that case.
+        */
        if (wal_level == WAL_LEVEL_LOGICAL || CheckLogicalSlotExists())
                new_status = true;