NodeJS Server hang on caused by limit MySQL connection.

MySQL server hang on. No error log shown.
Check processes see that mysqld use about 30% (of 512MB RAM). CPU idle.
Show full processlist in >mysql show about 11 connection
ie:
+----+------+-----------------+------+---------+------+----------+------
| Id | User | Host            | db   | Command | Time | State    | Info 
+----+------+-----------------+------+---------+------+----------+------
| 87 | root | localhost       | txp1 | Query   |    0 | starting | show 
| 88 | root | localhost:50190 | txp1 | Sleep   |    3 |          | NULL 
| 89 | root | localhost:50192 | txp1 | Sleep   |    3 |          | NULL 
+----+------+-----------------+------+---------+------+----------+------

...

I guest this is the caused by MySQL refuse to run query and/or some query hang on.

Then I try connect half dozen of devices include iPhone, Android, Genymotion, PC ... to figure out how new DB connection made when new client access server.

When a machine (device) connect to server, via web I realize that It only create ONE connection to DB. When a mobile device connect to server, Server create few connection to DB.

When a number of connection reach, in my case default node-mysql is 11 connections, it hang on. No more connection created and server hang on.

So I guest that the limit of mysql-node connection caused server Node hang on.

Then I update config mysql add limit connection:

function db() {

/*

creating MySql database connection 

*/

var con = mysql.createPool({

host : 'localhost',

  user : 'root',

  password : '******',

  database : 'db_one',

  port: 3306,

connectionLimit: 100

});

this.connection=con;

}

Then restart server and problem gone.