Re: EXPLAIN/EXPLAIN ANALYZE REFRESH MATERIALIZED VIEW

On Tue, 16 Mar 2021 at 20:13, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com> wrote:
> On Tue, Mar 16, 2021 at 1:15 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>
>> [ Sorry for not looking at this thread sooner ]
>>
>> Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.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.

+1.

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Japin Li.
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