Date: Thu, 20 Jun 2019 13:13:35 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Michael Lewis <mlewis@entrata.com>
Cc: Simon Riggs <simon@2ndquadrant.com>,
	Chris Wilson <chris.wilson@cantabcapital.com>,
	pgsql-performance@postgresql.org
Subject: Re: EXPLAIN ANALYZE of BRIN bitmap index scan with disjunction
Message-ID: <20190620181335.GY16019@telsasoft.com>
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On Thu, Jun 20, 2019 at 12:09:13PM -0600, Michael Lewis wrote:
> For kicks I tried the example given and got the below which seems more
> expected.

Do you just mean that it ran faster the 2nd time ?  Isn't that just due just to
cache effects ?  Rerun them both back to back.

See that the "actual" rowcount of the Index Scan is higher with tigher
condition:

>   ->  Bitmap Index Scan on idx_brin_test_brin  (cost=0.00..3.32 rows=14286 width=0) (actual time=0.018..0.019 rows=640 loops=1)
>         Index Cond: (id >= 90000)

>   ->  Bitmap Index Scan on idx_brin_test_brin  (cost=0.00..3.31 rows=7143 width=0) (actual time=0.026..0.027 rows=1280 loops=1)
>         Index Cond: ((id >= 90000) AND (r = ANY ('{1,3}'::integer[])))