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Re: Constant "JTable" update

From: Per-Olof Norén <pelle(at)alma(dot)nu>
To: "Jean-Christophe ARNU" <arnu(at)paratronic(dot)fr>, <pgsql-jdbc(at)postgresql(dot)org>
Subject: Re: Constant "JTable" update
Date: 2001-11-09 13:05:21
Message-ID: 007101c1691f$306ac1d0$d31014ac@lpernor (view raw or flat)
Thread:
Lists: pgsql-jdbc
----- Original Message -----
From: "Jean-Christophe ARNU" <arnu(at)paratronic(dot)fr>
To: <pgsql-jdbc(at)postgresql(dot)org>
Sent: Thursday, November 08, 2001 10:38 PM
Subject: [JDBC] Constant "JTable" update


> The straightforward solution seems to have database listeners on the
> table that wakes-up a notifier in the java program. But such kind of
> mechanism seems not to be implemented in the JDBC API (up to my small
> knowledge).

I haven´t seen such a mechanism, either :-)


> The second tortuous solutions (the one I use) is to query the database
> relatively often to get the freshest results. This is quite bandwidth
> consumming (assuming that some users should use a quite small bandwidth
> connection). Using this kind of solution makes the Java application
> slow...
First of all, this is how I interpreted your config.
You do a executeQuery once the rendering of the chart is done for one
execution?
And you process the entire ResultSet everytime, even though no changes are
made?

If this is the case, I would suggest a change in the following direction:
1. Create a little status table containing just one column: create table
last_change (lastchange datetime). Also add one row to the table
2. Create a trigger on the measurer table, that updates the date of the
status table.
3. Design your algorithm something like this


check status by executing a select on status table.

if changed {
    store the date from status query
    execute data query
    render chart
}

This would reduce the bandwith by not sending the resultset when no changes
are made.

By measuring the average change in time between , say the last five updates
to the status table, you
could even put the rendering of the chart in its on thread and let it sleep
a little shorter than the average time

Regards,
Per-Olof Norén




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