Re: failing to use index on UNION of matviews (Re: postgresql 10.1 wrong plan in when using partitions bug)

Ooo. I wasn't aware of that option. (Learn something new every day!)

Setting enable_seqscan=off takes one of the shorter queries I was working
with from about 3 minutes to 300ms. This is a comparable performance
improvement to where I put a materialized view (with indexes) on top of the
materialized views instead of using a simple view on top of the
materialized views. I'll have to try it with the query that takes 12 hours.

I built a test case, but can't get it to reproduce what I'm seeing on my
production database (it keeps choosing the indexes). I'm still fiddling
with that test case so I can easily share it. I'm also back to trying to
figure out what is different between my laptop database and the test case I
built and the real world query with the real data, and pondering the worst
query itself to see if some sort of re-write will help.

On Tue, Feb 6, 2018 at 1:18 PM, Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:

> On Sun, Feb 04, 2018 at 11:04:56AM -0500, Rick Otten wrote:
> > On Sun, Feb 4, 2018 at 10:35 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >
> > > Rick Otten <rottenwindfish(at)gmail(dot)com> writes:
> > > > I'm wrestling with a very similar problem too - except instead of
> > > official
> > > > partitions I have a views on top of a bunch (50+) of unioned
> materialized
> > > > views, each "partition" with 10M - 100M rows. On 9.6.6 the queries
> would
> > > > use the indexes on each materialized view. On 10.1, every
> materialized
> > > > view is sequence scanned.
>
> I think it'd be useful to see the plan from explain analyze, on both the
> "parent" view and a child, with and without SET enable_seqscan=off,
>
> Justin
>