Re: EXPLAIN/EXPLAIN ANALYZE REFRESH MATERIALIZED VIEW

On Tue, Mar 16, 2021 at 1:15 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> [ Sorry for not looking at this thread sooner ]
>
> Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> writes:
> > Currently, $subject is not allowed. We do plan the mat view query
> > before every refresh. I propose to show the explain/explain analyze of
> > the select part of the mat view in case of Refresh Mat View(RMV).
>
> TBH, I think we should reject this. The problem with it is that it
> binds us to the assumption that REFRESH MATERIALIZED VIEW has an
> explainable plan. There are various people poking at ideas like
> incremental matview updates, which might rely on some implementation
> that doesn't exactly equate to a SQL query. Incremental updates are
> hard enough already; they'll be even harder if they also have to
> maintain compatibility with a pre-existing EXPLAIN behavior.
>
> I don't really see that this feature buys us anything you can't
> get by explaining the view's query, so I think we're better advised
> to keep our options open about how REFRESH might be implemented
> in future.

That makes sense to me. Thanks for the comments. I'm fine to withdraw the patch.

I would like to see if the 0001 patch(attaching here) will be useful
at all. It just splits up the existing ExecRefreshMatView into a few
functions to make the code readable. I'm okay to withdraw it if no one
agrees.

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com