JDBC memory leaks

[Tyler Blair]

Hi everyone,

I seem to be having a problem with JDBC.. It leaks memory after some time. My application connects to MySQL to verify user accounts, uses it for logs, everything..

After a few hours, memory jogs up to 500mb+, and the evil user is:

com.mysql.jdbc.JDBC4Connection -> Shallow Heap [ 1,088 ] Retained Heap [ 495,884,816] Percentage [ 90,03% ]


For my ResultSets, I close them after, and close the statement as well. for querying I use PreparedStatements, in which I clear it and close it afterwards..



Example insertion using PreparedStatements: (for simplicity sakes, only one value)

		try {
			final PreparedStatement p = con
					.prepareStatement("INSERT INTO `chat_logs` SET `message` = ?");
			p.setString(1, "message");
			p.executeUpdate();
			p.clearParameters();
			p.close();
		} catch (final SQLException e) {
			System.err.println("MySQLException: " + e.getMessage());
		}

However, I've iterated that thousands upon thousands of times with static values. Memory usage goes up slightly and goes back down when the queries are done. As expected.



Querying:

		String temp = "";
		try {
			final ResultSet rs = executeQuery("SElECT `message` FROM `news` ORDER BY `id` ASC");
			while (rs.next()) {
				temp += rs.getString("message") + "\\n";
			}
			rs.close();
			stmt.close();
		} catch (final SQLException e) {
			e.printStackTrace();
		}
		return temp;

However, with this piece of code, the leak would happen WITHOUT the stmt.close(), when I added that, it no longer happened in the controlled scenario.


Connecting:

        final String username = "";
        final String password = "";
        final String host = "localhost";
	public boolean connect() {
		con = null;
		try {
			Class.forName("com.mysql.jdbc.Driver").newInstance();
			Properties prop = new Properties();
			prop.put("user", username);
			prop.put("password", password);
			prop.put("autoreconnect", "true");
			con = DriverManager.getConnection("jdbc:mysql://" + host + "/"
					+ database, prop);
			if (!con.isClosed()) {
				return true;
			}
		} catch (final Exception e) {
		}
		return false;
	}

The leak also happened before I began using properties for connecting, so I don't think it's that somehow.



So.. If you see something that's out of place, that is probably it, thanks very much.