Re: Instead of using the bloom index, a parallel sequencial scan is used with this example

On Tue, Nov 5, 2019 at 08:28:57PM +0000, Daniel Westermann (DWE) wrote:
>
> >>On Thu, Oct 24, 2019 at 03:17:06PM +0000, PG Doc comments form wrote:
> >> The following documentation comment has been logged on the website:
> >>
> >>Page: https://www.postgresql.org/docs/12/bloom.html
> >> Description:
>
> >I cleaned up your script and created an SQL file that can be piped into
> >psql, attached. I see the bloomidx index being used without and with
> >the ANALYZE, output attached. I tested this on git master, and back
> >through PG 10. Would you please run these queries and post the output:
>
> Thanks for having a look, Bruce. You test case is not exactly the same as in
> the documentation. For you "temporary table" test case I indeed see the bloom
> index getting used. Doing the same with a normal table results in a parallel
> seq scan.

Ah, I see your point about the temporary tables. I have retested with
permanent tables, and see the same output you do. By reducing the
generate_series by 100x, I am able to get the desired EXPLAIN plans by
turning on/off various optimizer settings. I am attaching my test
script and its output.

I suggestion is what I reduce generate_series by 100x and update the
EXPLAIN plans in the docs. The docs are unclear on how these different
plans are generated, though I am not excited about adding the exact
optimizer settings to generate each plan.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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