On 2020-01-09 21:52, Tom Lane wrote:
Peter might remember more clearly, but I have a feeling that we concluded that the intent of the spec was for read-only-ness to disallow globally-visible changes in the visible database contents.
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.
VACUUM, for example, does not cause any visible change, so it should be admissible. REINDEX ditto. (We ignore here the possibility of such things causing, say, a change in the order in which rows are returned, since that's beneath the spec's notice to begin with.)
agreed
ANALYZE ditto, except to the extent that if you look at pg_stats you might see something different --- but again, system catalog contents are outside the spec's purview.
agreed
You could extend this line of argument, perhaps, far enough to justify ALTER SYSTEM SET as well. But I don't like that because some GUCs have visible effects on the results that an ordinary query minding its own business can get. Timezone is perhaps the poster child there, or search_path. If we were to subdivide the GUCs into "affects implementation details only" vs "can affect query semantics", I'd hold still for allowing ALTER SYSTEM SET on the former group. Doubt it's worth the trouble to distinguish, though.
ALTER SYSTEM is read only in my mind. -- Peter Eisentraut http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
