Assertion failure in pg_copy_logical_replication_slot()

[Fujii Masao]

Hi,

If restart_lsn of logical replication slot gets behind more than
max_slot_wal_keep_size from the current LSN, the logical replication
slot would be invalidated and its restart_lsn is reset to an invalid LSN.
If this logical replication slot with an invalid restart_lsn is specified
as the source slot in pg_copy_logical_replication_slot(), the function
causes the following assertion failure.

    TRAP: FailedAssertion("!logical_slot", File: "slotfuncs.c", Line: 727)

This assertion failure is caused by

        /* Copying non-reserved slot doesn't make sense */
        if (XLogRecPtrIsInvalid(src_restart_lsn))
                ereport(ERROR,
                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                 errmsg("cannot copy a replication slot that doesn't 
reserve WAL")));

I *guess* this assertion check was added because restart_lsn should
not be invalid before. But in v13, it can be invalid thanks to 
max_slot_wal_keep_size.
I think that this assertion check seems useless and should be removed in v13.
Patch attached. Thought?

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION

diff --git a/src/backend/replication/slotfuncs.c 
b/src/backend/replication/slotfuncs.c
index 06e4955de7..bc3fcbff4d 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -723,12 +723,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool 
logical_slot)
 
        /* Copying non-reserved slot doesn't make sense */
        if (XLogRecPtrIsInvalid(src_restart_lsn))
-       {
-               Assert(!logical_slot);
                ereport(ERROR,
                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                 errmsg("cannot copy a replication slot that 
doesn't reserve WAL")));
-       }
 
        /* Overwrite params from optional arguments */
        if (PG_NARGS() >= 3)