Justin Pryzby <pryzby(at)telsasoft(dot)com> writes:
> I've seen this message now a handful of times recently. It seems to happen
> overnight, during a maintenance job which reindex things, including system
> catalog indices.
> It's easy to reproduce error under 10.5, but not under 10.3 nor 10.4.
> while :; do for a in pg_class_oid_index pg_class_relname_nsp_index pg_class_tblspc_relfilenode_index; do psql ts -qc "REINDEX INDEX $a"; done; done&
This looks suspiciously like the issue under discussion in
https://www.postgresql.org/message-id/12259.1532117714%40sss.pgh.pa.us
As far as we can tell, that bug is a dozen years old, so it's not clear
why you find that you can reproduce it only in 10.5. But there might be
some subtle timing change accounting for that.
regards, tom lane