Why there are many connections in this case (MySQLNonTransientConnectionException) - mysql

Question

I am getting an exception using PreparedStatement to select.
Got an exception accessing TestCase data! null
Problem to connect.
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException:
Too many connections
Here is my code:
public Integer getTypeByInputAndProblemId(String inputTestCase, Long problemId) {
String sql = "SELECT type FROM test_case where problem_id= ? and input= ?";
Integer type = 0;
try {
PreparedStatement ps = connection.prepareStatement(sql);
ps.setLong(1, problemId);
ps.setString(2, inputTestCase);
ResultSet rs = ps.executeQuery();
if (rs.next()) {
type = new Integer(rs.getInt("type"));
}
rs.close();
ps.close();
} catch (Exception e) {
System.err.println("Got an exception accessing TestCase data! " + e.getMessage());
}
return type;
}
In line PreparedStatement ps = connection.prepareStatement(sql);
my problem is because connection sometimes is Null (the debug shows this).
I'm guessing this is because of many connections, but I don't know why this is happening.
I would like some help, please!

Answer 1

Yes, the issue happens because your server is reaching the max number of multiple connections accepted by your MySQL Server.
First, you need to see if you have a proper number configured in MySQL for multiple connections: max_connections. If this look low to you, you can increase this number in order to "fix" this issue.
Secondly, if the number makes sense, you're probably using more connections than you think you are. Probably because you're opening connections in your application and not closing them.
Check how many multiple connections your server have used so far.
show status like 'Max_used_connections';
This number is reset when you restart your database service.