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From: Bruce Momjian <bruce@momjian.us>
To: Daniel Westermann (DWE) <daniel.westermann@dbi-services.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Wrong example in the bloom documentation
Date: Mon, 26 Oct 2020 17:04:09 -0400
Message-ID: <20201026210409.GA4951@momjian.us> (raw)
In-Reply-To: <GVAP278MB01022477E6F7AE58E207CF25D2000@GVAP278MB0102.CHEP278.PROD.OUTLOOK.COM>
References: <ZR0P278MB0122119FAE78721A694C30C8D2340@ZR0P278MB0122.CHEP278.PROD.OUTLOOK.COM>
	<GVAP278MB01028F3C84C0A724412854EDD20B0@GVAP278MB0102.CHEP278.PROD.OUTLOOK.COM>
	<20201008162310.GA13054@momjian.us>
	<GVAP278MB010226D15C90933B3C2D198BD20B0@GVAP278MB0102.CHEP278.PROD.OUTLOOK.COM>
	<2622731.1602186212@sss.pgh.pa.us>
	<20201008195352.GA5062@momjian.us>
	<GVAP278MB01026C00EA4E25E35062483FD2080@GVAP278MB0102.CHEP278.PROD.OUTLOOK.COM>
	<20201009150832.GB1459@momjian.us>
	<20201015235019.GH3797@momjian.us>
	<GVAP278MB01022477E6F7AE58E207CF25D2000@GVAP278MB0102.CHEP278.PROD.OUTLOOK.COM>

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.

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

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






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  Subject: Re: Wrong example in the bloom documentation
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