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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> wrote:
>
> > Rick Otten <rottenwindfish@xxxxxxxxx> 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
