Re: CREATE/REFRESH MATERIALIZED VIEW planner difference?

> On Jun 1, 2021, at 2:20 PM, Vijaykumar Jain <vijaykumarjain(dot)github(at)gmail(dot)com> wrote:
>
> if you are not using it concurrently, can you confirm the there are *no active* queries on the mv.
> refresh requires AccessExclusiveLock and will wait, till it gets one.
> just asking if you can rule out the extended time is not due to waiting for lock.

I can confirm that it’s not waiting on a lock. In addition, through the AWS CPU utilization monitor I can see that the REFRESH uses one CPU/worker whereas the CREATE uses four. This is consistent with the EXPLAIN ANALYZE for the CREATE which says it uses four workers.

> also, can you share the plans where you see the diff.

Unless I misunderstand, there is no plan for a REFRESH.

EXPLAIN (ANALYZE, BUFFERS) refresh materialized view my_mat_view
+-------------------------------------------+
| QUERY PLAN |
|-------------------------------------------|
| Utility statements have no plan structure |
+-------------------------------------------+

Cheers
Philip

>
> On Tue, 1 Jun 2021 at 23:30, Philip Semanchuk <philip(at)americanefficient(dot)com> wrote:
> Hi all,
> Should I expect a planner difference between CREATE MATERIALIZED VIEW and REFRESH MATERIALIZED VIEW? We have a materialized view that uses 4 workers during CREATE but only one worker during REFRESH, and as a result the refresh takes much longer (~90 minutes vs. 30 minutes for the CREATE). So far this behavior has been 100% consistent.
>
> I'm running both the CREATE and REFRESH on the same server (Postgres 11.9 on AWS Aurora). I don't think the refresh is using one worker in response to other things happening on the server because we’ve observed this happening when the server is not busy. We're not using the CONCURRENTLY option for REFRESH.
>
> THanks
> Philip
>
>
>
> --
> Thanks,
> Vijay
> Mumbai, India