This would be the fastest way
$local = PDO connection to database on local db server
$remote = PDO connection to database on remote server
//
// GET DATA FROM LOCAL SERVER
//
$res = $local->query("SELECT user_id, user_username FROM users");
$users = [];
foreach ($res as $row) {
$users[] = vsprintf("(%d, '%s')", $row);
}
//
// WRITE DATA TO REMOTE SERVER
// 1,000 RECORDS AT A TIME
//
$chunks = array_chunk($users, 1000);
$count = 0;
foreach ($chunks as $data) {
$count += $remote->exec("INSERT INTO users (id, username) VALUES " . join(',', $data));
}
echo "$count records transferred";