Difference between mysql.createConnection and mysql.createPool in Node.js?

mysql.createConnection

When you create a connection with mysql.createConnection, you only have one connection and it lasts until you close it OR connection closed by MySQL.

A single connection is blocking. While executing one query, it cannot execute others. hence, your application will not perform good.
Example:

var mysql = require('mysql');
var connection = mysql.createConnection({
  host     : 'localhost',
  user     : 'root',
  password : '',
  database : 'mydb',
});

mysql.createPool

mysql.createPool is a place where connections get stored.
When you request a connection from a pool,you will receive a connection that is not currently being used, or a new connection.
If you're already at the connection limit, it will wait until a connection is available before it continues.

A pool while one connection is busy running a query, others can be used to execute subsequent queries. Hence, your application will perform good.
Example:

var mysql = require('mysql');
var pool  = mysql.createPool({
  connectionLimit : 10,
  host     : 'localhost',
  user     : 'root',
  password : '',
  database : 'mydb',
});

How to check active connections in MySQL?

Question: How to check active connections in mysql?

show status where `variable_name` = 'Threads_connected';

Question: How to check the limit of MySQL active connections?

SHOW VARIABLES LIKE "max_connections";

Question: Display the list of active MySQL Process list?

show processlist;

Question: How to check the max no of connections used?

SHOW STATUS WHERE `variable_name` = 'Max_used_connections';

Question: MySQL set the max no of connections used (Temporarily/Quick)?

SET GLOBAL max_connections = 512;

Question: MySQL set the max no of connections used (Temporarily/Quick)?
Open my.cnf or my.ini in MySQL

max_connections = 512

service mysqld restart

Question: MySQL check number of connections throughout history?

show status like 'Connections%';