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

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От Rick Otten
Тема Re: failing to use index on UNION of matviews (Re: postgresql 10.1wrong plan in when using partitions bug)
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Msg-id CAMAYy4+zwbK=beZnC=7NM1hiGDsrK8RLYUVh5e6seK+9X4s01A@mail.gmail.com
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Ответ на Re: failing to use index on UNION of matviews (Re: postgresql 10.1wrong plan in when using partitions bug)  (Justin Pryzby <pryzby@telsasoft.com>)
Ответы Re: failing to use index on UNION of matviews (Re: postgresql 10.1wrong plan in when using partitions bug)  (Rick Otten <rottenwindfish@gmail.com>)
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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@telsasoft.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@sss.pgh.pa.us> wrote:
>
> > Rick Otten <rottenwindfish@gmail.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

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