Reject COPY TO of unlogged relations during recovery

Hi

While testing the unlogged materialized views patch I noticed that copy
with an unlogged table from a standby tries to read a file that does not
exist on disk:

== primary ==

psql (20devel)
Type "help" for help.

postgres=# create unlogged table ut as select 1;
SELECT 1

== standby ==

psql (20devel)
Type "help" for help.

postgres=# copy ut to stdout;
ERROR: could not open file "base/5/16384": No such file or directory

I could reproduce this bug on PG14 as well:

== primary ==

psql (14.23 (Debian 14.23-1.pgdg13+1))
Geben Sie »help« für Hilfe ein.

postgres=# create unlogged table ut1 as select 1;
SELECT 1

== standby ==

psql (14.23 (Debian 14.23-1.pgdg13+1))
Geben Sie »help« für Hilfe ein.

postgres=# copy ut1 to stdout;
ERROR: could not open file "base/13759/772691051": No such file or
directory

I did some digging and found this thread[1] fixing a similar problem in
pg_dump, but I couldn't find anything similar on the server. I managed
to get a proper error message by adding a check in copyto.c (patch
attached), but I'm not sure this is the right place for it.

psql (20devel)
Type "help" for help.

postgres=# copy ut to stdout;
ERROR: cannot access temporary or unlogged relations during recovery

Before I put too much effort on tests I would like to hear your thoughts
on the approach.

Best, Jim

1 -
https://www.postgresql.org/message-id/flat/E1TutDO-0001Hb-2v%40wrigleys.postgresql.org