var pool = mysql.createPool({
    host: databaseHost,
    user: databaseUser,
    password: databasePassword,
    database: databaseName,
    multipleStatements: true
});

pool.getConnection(function (err, connection) {
    if (err) {
        callback(err);
    } else {
        // Use the connection

        var sql = "...sql statement...";
        var inserts = [...inserts...];

        connection.query(sql, inserts, function (error, results, fields) {

            // And done with the connection.
            connection.release();

            // Handle error after the release.
            if (error) {
                callback(error);
            } else {
                callback(null, results);
            }
        });
    }
});

"ER_CON_COUNT_ERROR: Too many connections"

console.log(pool.config.connectionLimit);     // passed in max size of the pool
console.log(pool._freeConnections.length);    // number of free connections awaiting use
console.log(pool._allConnections.length);     // number of connections currently created, including ones in use
console.log(pool._acquiringConnections.length); // number of connections in the process of being acquired

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