It’s been a while since the last time i’ve write tutorials in my blog, but i found a very interesting case that perhaps helped a lot of people. Today im trying to create a simple test case to simulate a connection leak and how to search for it.

First is creating a simple unclosed connection query using java,

package com.edw;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class Main {

    public static void main(String[] args) throws Exception {
        System.out.println("starting --------");
        
        Class.forName("oracle.jdbc.driver.OracleDriver");
        Connection connection = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe", "USERNAME", "password");
        Statement statement = connection.createStatement();
        ResultSet resultSet = statement.executeQuery("SELECT * FROM INVALID"); // example table name is INVALID
        
        while(resultSet.next()) {
            System.out.println(resultSet.getString(1));
            System.out.println(resultSet.getString(2));
            System.out.println(resultSet.getString(3));
            System.out.println("=============");
        }
        
        System.out.println("ending --------");
        
        while(true) {
            Thread.sleep(10000);
            System.out.println("testing --------");
        }
    
    }
}

It will create an unclosed query that will hanging on my oracle connection.
And next, is my oracle query to find the hanging queries,

select LAST_CALL_ET, SQL_TEXT, username, machine, to_char(logon_time, 'ddMon hh24:mi') as login, 
    SQL_HASH_VALUE, PREV_HASH_VALUE, status
from v$session, v$sql 
where username='USERNAME' and HASH_VALUE =  PREV_HASH_VALUE
order by last_call_et desc;

it will show result like this,

LAST_CALL_ET SQL_TEXT                USERNAME     MACHINE        LOGIN                SQL_HASH_VALUE PREV_HASH_VALUE STATUS 
------------ ---------------------- ------------- -------------- -------------------- -------------- --------------- --------
          91 SELECT * FROM INVALID   USERNAME     edw      	     03Mar 11:53                       0       621168917 INACTIVE 

As you can see the result on the first column, “SELECT * FROM INVALID” query has run for more than 90 seconds.
So i can easily find the java class culprit who run that query.

FYI, this is my Oracle version,

select * from v$version;

BANNER                                                                         
--------------------------------------------------------------------------------
Oracle Database 11g Express Edition Release 11.2.0.2.0 - Production              
PL/SQL Release 11.2.0.2.0 - Production                                           
CORE	11.2.0.2.0	Production                                                         
TNS for 32-bit Windows: Version 11.2.0.2.0 - Production                          
NLSRTL Version 11.2.0.2.0 - Production   

I Hope this tutorial can help others, have fun 🙂