Re: Wrong example in the bloom documentation

On Mon, Oct 26, 2020 at 05:04:09PM -0400, Bruce Momjian wrote:
> On Sat, Oct 17, 2020 at 01:50:26PM +0000, Daniel Westermann (DWE) wrote:
> > On Fri, Oct  9, 2020 at 11:08:32AM -0400, Bruce Momjian wrote:
> > >This is not applying to PG 12 or earlier because the patch mentions JIT,
> > >which was only mentioned in the PG bloom docs in PG 13+.
> > 
> > Does that mean we need separate patches for each release starting with 10? 
> > As I am not frequently writing patches, I would need some help here.
> 
> I can regenerate the output for older versions using your patch.
> However, I am confused about the parallelism you are seeing.  Your patch
> shows:
> 
>        Without the two indexes being created, a parallel sequential scan will happen for the query below:
>                                                 -------------------
>     <programlisting>
>     =# EXPLAIN ANALYZE SELECT * FROM tbloom WHERE i2 = 898732 AND i5 = 123451;
>                                                 QUERY PLAN
>     ---------------------------------------------------------------------------------------------------
>      Seq Scan on tbloom  (cost=0.00..214.00 rows=1 width=24) (actual time=2.729..2.731 rows=0 loops=1)
>        Filter: ((i2 = 898732) AND (i5 = 123451))
>        Rows Removed by Filter: 10000
>      Planning Time: 0.257 ms
>      Execution Time: 2.764 ms
>     (5 rows)
> 
> However, I don't see any parallelism in this output.  Also, I don't see
> any parallelism once the indexes are created.  What PG version is this?
> and what config settings did you use?  Thanks.

I figured it out --- you have to use the larger generate_series value to
get the parallel output.  I have adjusted all the docs back to 9.6 to
show accurate output for that version, and simplified the query
ordering --- patch to master attached.  The other releases are similar. 
Daniel, please let me know if I have left out any details.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

  The usefulness of a cup is in its emptiness, Bruce Lee