> can the previous error path in
> mark_index_clustered() be reached through a different mean than ALTER
> TABLE?
That was one of the things we discussed in the previous emails. The
remaining callers of that function are VACUUM FULL and CLUSTER. It
definitely can't be hit by VACUUM (it passes an InvalidOid for an
index), but CLUSTER is a bit more difficult to follow. It seems like
to me that it shouldn't be hit (CLUSTER only calls it for leaf
partitions, where the check will be false), but I'm not 100% sure
about my diagnosis.