Laravel：如何设置数据库连接池？

Question

I need to connect many databases dynamically in laravel app.
How to set database connection pool?

for example,there are many second-class domain name,like this:

chicago.example.com
newyork.example.com
losangeles.example.com
...

They have separate database:

chicago
newyork
losangeles
...

I connect these databases dynamically like this:

public function store(Request $request)
{
    //post request from http://chicago.example.com/articles
    $server_name_arr=explode('.',$_SERVER['SERVER_NAME']); //the result is ['chicago','example','com']
    $db=array_slice($server_name_arr,-3,1)[0]; //the result is 'chicago'

    Config::set('database.connections.mysql.database', $db);
    DB::reconnect('mysql');

    //...
}

For performance,I want to set database connection pool,how to do it in laravel?