Re: our checks for read-only queries are not great

Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com> writes:
> I don't really remember, but that was basically the opinion I had
> arrived at as I was reading through this current thread. Roughly
> speaking, anything that changes the database state (data or schema) in a
> way that would be reflected in a pg_dump output is not read-only.

OK, although I'd put some emphasis on "roughly speaking".

> ALTER SYSTEM is read only in my mind.

I'm still having trouble with this conclusion. I think it can only
be justified by a very narrow reading of "reflected in pg_dump"
that relies on the specific factorization we've chosen for upgrade
operations, ie that postgresql.conf mods have to be carried across
by hand. But that's mostly historical baggage, rather than a sane
basis for defining "read only". If somebody comes up with a patch
that causes "pg_dumpall -g" to include ALTER SYSTEM SET commands for
whatever is in postgresql.auto.conf (not an unreasonable idea BTW),
will you then decide that ALTER SYSTEM SET is no longer read-only?
Or, perhaps, reject such a patch on the grounds that it breaks this
arbitrary definition of read-only-ness?

As another example, do we need to consider that replacing pg_hba.conf
via pg_write_file should be allowed in a "read only" transaction?

These conclusions seem obviously silly to me, but perhaps YMMV.

regards, tom lane