From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: our checks for read-only queries are not great |
Date: | 2020-01-10 14:29:58 |
Message-ID: | 26383.1578666598@sss.pgh.pa.us |
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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
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