Re: Fix "unexpected logical decoding status change" error; from concurrent logical decoding activation - Mailing list pgsql-hackers

On Thu, Jul 16, 2026 at 6:52 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Tue, Jul 14, 2026 at 2:02 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> These races are confined to the narrow window between checking the
> logical decoding status and the new slot becoming visible; once the
> slot is visible, the invalidation performed by the deactivation
> already covers it. So the fix is simple: re-check the logical decoding
> status after the new slot becomes visible.
>

*
- * CheckLogicalDecodingRequirements() must have already errored out if
- * logical decoding is not enabled since we cannot enable the logical
- * decoding status during recovery.
+ * The caller has already checked that logical decoding is enabled via
+ * CheckLogicalDecodingRequirements(), but the status could have been
+ * disabled concurrently before our slot being created: either by
+ * replaying an XLOG_LOGICAL_DECODING_STATUS_CHANGE record, or by
+ * UpdateLogicalDecodingStatusEndOfRecovery() upon promotion. We
+ * cannot enable logical decoding during recovery, so raise an error.
  */
- Assert(IsLogicalDecodingEnabled());
+ if (!IsLogicalDecodingEnabled())
+ ereport(ERROR,
+ (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+ errmsg("logical decoding on standby requires \"effective_wal_level\"
>= \"logical\" on the primary"),
+ errdetail("Logical decoding was concurrently disabled during the
logical replication slot creation.")));

It is not clear after reading the comment above this check what kind
of interlocking would save us from concurrent deactivation by two ways
mentioned by you immediately after this check?

--
With Regards,
Amit Kapila.