From: Achilleas Mantzios - cloud <a.mantzios@cloud.gatewaynet.com>
To: pgsql-performance@lists.postgresql.org
Subject: pgsql 10.23 , different systems, same table , same plan, different Buffers: shared hit
Date: Fri, 15 Sep 2023 17:30:39 +0300
Message-ID: <24a36ca8-b5c0-d39f-c5f6-47cf2ef51abd@cloud.gatewaynet.com> (raw)
Dear All
I have a weird problem, I am trying to improve performance on this query :
SELECT text('foo@bar.com') from mail_vessel_addressbook where
text('foo@bar.com') ~* address_regex limit 1;
The first system (linux) is a linux hosted in a cloud, kernel
3.16.0-4-amd64, 32GB mem, SSD, 4 x Intel(R) Xeon(R) CPU E7-4860 v2 @
2.60GHz ,
The second (freebsd) system, used as test, is my local FreeBSD
13.1-RELEASE workstation, 32GB mem, ZFS/magnetic disks ,16 x AMD Ryzen 7
5800X 3800.16-MHz .
Overall my workstation is faster, but my issue is not plain speed. The
problem is as follows :
*FreeBSD*
postgres@[local]/dynacom=# explain (analyze,buffers) SELECT
text('foo@bar.com') from mail_vessel_addressbook where
text('foo@bar.com') ~* address_regex limit 1;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.42..5.11 rows=1 width=32) (actual time=96.705..96.706
rows=1 loops=1)
Buffers: shared hit=71
-> Index Only Scan using mail_vessel_addressbook_address_regex_idx
on mail_vessel_addressbook (cost=0.42..2912.06 rows=620 width=32)
(actual time=96.704..96.705 rows=1 loops=1)
Filter: ('foo@bar.com'::text ~* address_regex)
Rows Removed by Filter: 14738
Heap Fetches: 0
Buffers: shared hit=71
Planning time: 0.082 ms
Execution time: 96.725 ms
(9 rows)
Time: 97.038 ms
postgres@[local]/dynacom=#
*Linux*
dynacom=# explain (analyze,buffers) SELECT text('foo@bar.com') from
mail_vessel_addressbook where text('foo@bar.com') ~* address_regex limit 1;
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.42..5.12 rows=1 width=32) (actual time=1768.725..1768.727
rows=1 loops=1)
Buffers: shared hit=530
-> Index Only Scan using mail_vessel_addressbook_address_regex_idx
on mail_vessel_addressbook (cost=0.42..2913.04 rows=620 width=32)
(actual time=1768.724..1768.725 rows=1 loops=1)
Filter: ('foo@bar.com'::text ~* address_regex)
Rows Removed by Filter: 97781
Heap Fetches: 0
Buffers: shared hit=530
Planning time: 1.269 ms
Execution time: 1768.998 ms
(9 rows)
The file in FreeBSD came by pg_dump from the linux system, I am puzzled
why this huge difference in Buffers: shared hit. All table/index sizes
are identical on both systems, I did vacuum full on the linux one, and
also did vacuum freeze on both. I analyzed both, reindexed both (several
times). Still the FreeBSD seems to access about 7 times less number of
blocks from shared_buffers than linux : 71 vs 530 . There is no bloat ,
I tested with newly fresh table in both systems as well.
Thank you for any help.
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To: pgsql-performance@postgresql.org
Cc: a.mantzios@cloud.gatewaynet.com, pgsql-performance@lists.postgresql.org
Subject: Re: pgsql 10.23 , different systems, same table , same plan, different Buffers: shared hit
In-Reply-To: <24a36ca8-b5c0-d39f-c5f6-47cf2ef51abd@cloud.gatewaynet.com>
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