From: John Top-k apad <topkapad@gmail.com>
To: pgsql-performance@postgresql.org
Subject: Variation between query runtimes
Date: Sun, 11 Jun 2006 09:35:20 +0300
Message-ID: <5809b390606102335j41f734d8j@mail.gmail.com> (raw)
Hi,
I have the following quering plans:
"Seq Scan on ind_uni_100 (cost=0.00..27242.00 rows=1000000 width=104)
(actual time=0.272..2444.667 rows=1000000 loops=1)"
"Total runtime: 4229.449 ms"
and
"Bitmap Heap Scan on ind_uni_100 (cost=314.00..18181.00 rows=50000
width=104) (actual time=74.106..585.368 rows=49758 loops=1)"
" Recheck Cond: (b = 1)"
" -> Bitmap Index Scan on index_b_ind_uni_100
(cost=0.00..314.00rows=50000 width=0) (actual time=
61.814..61.814 rows=49758 loops=1)"
" Index Cond: (b = 1)"
"Total runtime: 638.787 ms"
from pg_stast_get_blocks_fetched i can see that both queries need almost the
same number of disk fetches which is quite reasonable ( the index is
unclustered).
But as you can see there is a great variation between query
runtimes.Cansomeone explain this differnce?
Thanks!
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: topkapad@gmail.com
Subject: Re: Variation between query runtimes
In-Reply-To: <5809b390606102335j41f734d8j@mail.gmail.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox