Invoking MySQL

Basic PDO interface is supported for communication with MySQL databases. You can see the actual interface here.

With it you can execute simple text SQL queries:

function sample(string $mysql_host, int $mysql_port, string $dbname, string $user, string $password) {
  // Create the connection:
  $db = new PDO(
    [PDO::ATTR_TIMEOUT => 2]  // Only PDO::ATTR_TIMEOUT option is supported
  // Send simple SELECT like text query:
  $stmt = $db->query("SELECT * FROM SomeTable");
  if ($db->errorCode() == 0) {  // Simple error handling
  $res = $stmt->fetchAll();
  // Send simple modify text query:
  $affected_rows = $db->exec("DELETE FROM SomeTable WHERE id=42");

Note: Only default behaviour is supported for exposed methods.
Particularly, it means that features like Prepared statements, Unbuffered fetching mode are not supported so far.

Note: But the advantage of this PDO::MySQL version is asynchronicity. The main communication methods like PDO::query and PDO::exec are marked as resumable functions.
It means that these method calls will be considered as suspendable points by other resumable functions (a.k.a. coroutines).

Also KPHP implements some mysqli_…() functions, that can be called MySQL support somehow.

But at, we use a special db-proxy layer between KPHP and MySQL databases. It is a daemon running on every server: it manages connections, performs master-replica routing, handles access rights.

As a result, KPHP just skips credentials passed to mysqli_connect(). Moreover, MySQL connection can only be opened to localhost with unix socket.