From: Richard Huxton <dev@archonet.com>
To: Joel Fradkin <jfradkin@wazagua.com>
Cc: gsstark@mit.edu
Cc: pgsql-sql@postgresql.org
Subject: Re: same question little different test MSSQL vrs Postgres
Date: Wed, 26 Jan 2005 15:20:44 +0000
Message-ID: <41F7B54C.5020204@archonet.com> (raw)
In-Reply-To: <000001c503b7$6ea08800$797ba8c0@jfradkin>
References: <000001c503b7$6ea08800$797ba8c0@jfradkin>
Joel Fradkin wrote:
> Well last evening (did not try it this morning) it was taking the extra
> time.
>
> I have made some adjustments to the config file per a few web sites that you
> all recommended my looking at.
The crucial one I'd say is the performance guide at:
http://www.varlena.com/varlena/GeneralBits/Tidbits/index.php
The first half-dozen settings are the crucial ones.
> It is now using 137 of 756 meg avail.
> it is now taking 8 secs to return 22,000 rows (using pgadminIII in a sql
> edit window).
That might be too much RAM. Don't forget PG likes to work with your
operating-system (unlike many other DBs). Make sure Windows is using
enough RAM to cache diskspace.
I'm curious as to how this takes 8secs whereas you had 1 second earlier.
Are you sure some of this isn't pgadmin's overhead to display the rows?
> The EXPLAIN ANALYSE still shows the same as below, but the table has 344,000
> recs of which only 22636 are clientnum = 'SAKS'
That sounds like it's about the borderline between using an index and
not (depending on cache-size, disk speeds etc).
> I am still doing a seq search (this applies to the view question where if it
> is a small result set it used a index search but on a larger return set it
> did a seq search) in my view, but with the adjustments to the kernel I get a
> result in 140 secs (MSSQL was 135 secs).
If you want to check whether the index would help, try issuing the
following before running your query:
SET ENABLE_SEQSCAN=FALSE;
This will force PG to use any index it can regardless of whether it
thinks it will help.
> This is not production, I am still very worried that I have to do all this
> tweeking to use this, MSSQL worked out of the box as it does (not saying its
> great, but I never had to adjust a kernel setting etc). Since we cannot
> afford the 70,000 dollars they want to license it I am not implying I can
> use MSSQL, but I could look at other DB's like MYSQL, or Firebird, etc.
I'm a little curious what kernel settings you are changing on Windows. I
wasn't aware there was much to be done there.
I'm afraid you do have to change half a dozen settings in
postgresql.conf to match your workload, but PG runs on a much wider
range of machines than MSSQL so it's difficult to come up with a
"reasonable" default. Takes me about 5 minutes when I setup an
installation to make sure the figures are reasonable (rather than the
best they can be).
> I have a lot of time now (two weeks) in this conversion and do not wish to
> give up, I will see if I can learn what is needed to get the maximum
> performance. I have seen much information available and this list has been a
> huge resource. I really appreciate all the help.
--
Richard Huxton
Archonet Ltd
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To: pgsql-sql@postgresql.org
Cc: dev@archonet.com, jfradkin@wazagua.com, gsstark@mit.edu
Subject: Re: same question little different test MSSQL vrs Postgres
In-Reply-To: <41F7B54C.5020204@archonet.com>
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