From: | Andreas Hartmann <andreas(at)apache(dot)org> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Massive performance differences |
Date: | 2005-03-15 17:37:48 |
Message-ID: | d176f4$7s7$1@sea.gmane.org |
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Lists: | pgsql-general |
Andreas Hartmann wrote:
> Hi all,
>
> I'm running the same database on two systems:
>
> A) Debian PostgreSQL 7.4.7
> B) SuSE PostgreSQL 7.3.4
>
> Both machines have approx. 1GHz and 1GB RAM.
> The amount of data is almost equal (+- 10%). But I'm facing
> huge performance differences. For instance, a simple sequential
> scan results in the following query plans:
[...]
I just imported a dump of (B) into (A) to be sure to have the
same data set. When I executed the query on (A) the first time, it was
as slow as on (B). But the next time it was significantly faster:
vvz_dev=> explain analyze select * from veranstaltung_original order by semester;
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------
Sort (cost=587.08..600.74 rows=5467 width=229) (actual
time=3188.975..3192.020 rows=5467 loops=1)
Sort Key: semester
-> Seq Scan on veranstaltung_original (cost=0.00..247.67 rows=5467
width=229) (actual time=2.330..1587.832 rows=5467 loops=1)
Total runtime: 3205.281 ms
(4 Zeilen)
vvz_dev=> explain analyze select * from veranstaltung_original order by semester;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------
Sort (cost=587.08..600.74 rows=5467 width=229) (actual time=95.061..98.143
rows=5467 loops=1)
Sort Key: semester
-> Seq Scan on veranstaltung_original (cost=0.00..247.67 rows=5467
width=229) (actual time=0.015..7.749 rows=5467 loops=1)
Total runtime: 102.948 ms
(4 Zeilen)
This leads to the idea that it might be a caching problem.
How can I confirm this?
-- Andreas
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