Re: UNION causes horrible plan on JOIN

[Craig James <cjames@xxxxxxxxxxxxxx>]

On Mon, Oct 28, 2019 at 4:31 PM Justin Pryzby <pryzby@xxxxxxxxxxxxx> wrote:

On Mon, Oct 28, 2019 at 04:30:24PM -0700, Craig James wrote:
> On Mon, Oct 28, 2019 at 3:45 PM Justin Pryzby <pryzby@xxxxxxxxxxxxx> wrote:
>
> > On Mon, Oct 28, 2019 at 03:40:58PM -0700, Craig James wrote:
> > > On Postgres 9.6 (config below), I have a case I don't understand: three
> > > tables that can be separately queried in milliseconds, but when put
> > > together into one view using UNION, take 150 seconds to query. Here's the
> > > rough idea (actual details below):
> >
> > Do you want UNION ALL ?
> >
> > UNION without ALL distintifies the output.
> > https://www.postgresql.org/docs/current/sql-select.html#SQL-UNION
>
>
> Interesting idea, thanks. But it makes no difference. Tried it and got the
> same bad performance.

Could you mail the list the plan with union ALL ?

Here it is. It is indeed different, but takes 104 seconds instead of 140 seconds.

https://explain.depesz.com/s/zW6I 

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Craig A. James

Chief Technology Officer

eMolecules, Inc.

3430 Carmel Mountain Road, Suite 250

San Diego, CA 92121

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