Re: JDBC ResultSet writes to tmp file
- From: "Robert Klemme" <bob.news@xxxxxxx>
- Date: Thu, 12 May 2005 12:28:32 +0200
Hong wrote:
> The problem I got is when I am using the ResultSet to loop through the
> result rows, the JDBC driver keeps writing each row's data to a tmp
> file at /Tomcat/temp/ After the loop is finished, I do a
> "ResultSet.close();". After that, the content in that tmp file is
> gone.
>
> Because the content written to the tmp file is really big during the
> looping, it significantly slows done the performance.
Did you actually verify this with some measurements that the tmp file is
the reason for slow performance?
> Following is my
> code.
> [code]
> int size = 0;
> int i = 0;
> ObjectOutputStream outputToApplet = new
> ObjectOutputStream(response.
> getOutputStream());
> ResultSet resultSet = statement.executeQuery(q);
>
> if (page == 0) { //send back the number of rows.
> resultSet.last();
> size = resultSet.getRow();
> resultSet.beforeFirst();
>
> outputToApplet.writeObject(new Integer(size));
> outputToApplet.flush();
> }
> else if (page > 0) { //send back 1000 as the number of
> rows, and start from page*1000
> outputToApplet.writeObject(new Integer(1000));
> outputToApplet.flush();
> resultSet.absolute(page * 1000);
> }
>
> while (resultSet.next()) {
> String MailID = resultSet.getString("mail_Id");
> String Name = resultSet.getString("mailFrom");
> String To = resultSet.getString("mailToSorted");
> String Subject = resultSet.getString("Subject");
> String InsertDate = resultSet.getString("insertDate");
>
> CustomerServiceReturn C = new
> CustomerServiceReturn(Name, To, MailID, Subject, InsertDate);
>
> outputToApplet.writeObject(C);
> outputToApplet.flush();
>
> i++;
> if (i == 1000) {
> outputToApplet.close();
> resultSet.close();
> return;
> }
> }
>
> resultSet.close();
> outputToApplet.close();
> [/code]
> The name of the file is "ddtbxxxxx.tmp". xxxxx is a number.
>
> Thank you so much for any help.
I'd remove the invocations of "outputToApplet.flush();". Closing does a
flush automatically and with the flushes in between you underutilize the
streams buffers which might be *one* reasons for bad performance.
It's also a good idea to put close() calls into finally blocks. That way
you make sure that even in case of an exception resources are properly
deallocated.
Kind regards
robert
.
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- From: Hong
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