Hi!
Coments inline.
Regards.
João Paulo Ribeiro
Axel Wilhelm Berle wrote:
Hi Vladimir,
that's exactly the solution that I found. I examined
the code and pondered if I should do a hack. But than
I just set the DODS_HOME variable via
System.setProperty before launching DODS .. and it
worked.
Thanks for your help!
I still have some questions about the "correctness" of
DODS as a caching manager. One of my concernes is that
two or more threads access and try to update the same
DO (this concern has been mentioned in the online
manuals). How do I prevent this? (or how do I deal
with it?) Isn't that a major drawback?
The other question is, how do I use the SQL feature
OFFSET and LIMIT? Often you need just a "page" of a
table and it would be a big waste to load the entire
table and throw away the parts you don't need! The
best solution for this (I suppose the database
optimizes this) would be the use of OFFSET and LIMIT.
The problem with OFFSET and LIMIT is that if you need two pages you need two
offsets and you will need to do two queries.
Other points of view:
1) From a database point of view the best aproach is cursors.
The values are kep at db and you only fetch what you need when you need it.
If you need two page you only have to made one query and fetch the rows you
need. This spend db resources and is more dificult to control from a web
aplication point of view. You need the connection and resutset always open.
This used only for special data and special cases.
2) Application cache.
You can keep the values in cache and get them when you need.
The advantage is that you use less database resources and can improve speed if
the values are used by more than one user/application.
The Dods LRU cache can be a good approach for doing that.
Its the same approch as cursors but the data is kept at the application to be
fetched as you need it so the resources are spended at the aplication and not
the db.
I think this will be a better approach from a web application point of view.
I would like to use DODS for some work at a university
where I am tutoring some students and for this end I
feel that a more "scientific" documentation would be
necessary, explaining how the caching works, etc.
(well, this is just my personal whishing list!)
Thanks for your time,
Axel
Message: 2
Date: Wed, 26 Nov 2003 08:52:46 -0800 (PST)
From: Vladimir Ritz Bossicard <vbossica@xxxxxxxxx>
Subject: Re: Enhydra: Re: Dods standalone program
(Vladimir Ritz
Bossicard)
To: enhydra@xxxxxxxxxxx
Reply-To: enhydra@xxxxxxxxxxx
Still the same message: JVM can not find neither
DODS
HOME nor ENHYDRA HOME!
what I do is a HUGE hack. But it works:
1) set the dods home location in a property of the
servlet (web.xml
file)
<servlet>
<servlet-name>ApplicationGateway</servlet-name>
<init-param>
<param-name>DodsHome</param-name>
<param-value>/opt/java/install/dods-5.1</param-value>
</init-param>
<init-param>
<param-name>DodsConfig</param-name>
<param-value>/home/vladimir/proto/test/config/dods.conf</param-value>
</init-param>
2) in your servlet initialization code:
System.setProperty("DODS_HOME",
config.getInitParameter("DodsHome"));
DODS.startup(config.getInitParameter("DodsConfig"));
I won't say that it's a nice solution, but it does the
job.
hth
-Vladimir
=====
Vladimir Ritz Bossicard
www.bossicard.com
=====
Axel Wilhelm Berle
e-mail: axelberle@xxxxxxxx
Tel: (office) +55 16 618.0090
(mobile) +55 16 9964.6343
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