From: Tom Lane <tgl@sss.pgh.pa.us>
To: Achilleas Mantzios - cloud <a.mantzios@cloud.gatewaynet.com>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: pgsql 10.23 , different systems, same table , same plan, different Buffers: shared hit
Date: Fri, 15 Sep 2023 11:23:49 -0400
Message-ID: <3310210.1694791429@sss.pgh.pa.us> (raw)
In-Reply-To: <24a36ca8-b5c0-d39f-c5f6-47cf2ef51abd@cloud.gatewaynet.com>
References: <24a36ca8-b5c0-d39f-c5f6-47cf2ef51abd@cloud.gatewaynet.com>
Achilleas Mantzios - cloud <a.mantzios@cloud.gatewaynet.com> writes:
> *FreeBSD*
>
> -> 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
>
> *Linux*
>
> -> 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
> The file in FreeBSD came by pg_dump from the linux system, I am puzzled
> why this huge difference in Buffers: shared hit.
The "rows removed" value is also quite a bit different, so it's not
just a matter of buffer touches --- there's evidently some real difference
in how much of the index is being scanned. I speculate that you are
using different collations on the two systems, and FreeBSD's collation
happens to place the first matching row earlier in the index.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, 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: <3310210.1694791429@sss.pgh.pa.us>
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