Question

Does $this->db->insert_batch(); insert with 1 table connection or does it insert each row separately incurring overhead of opening connections?

Answer 1

From the documentation of code igniter insert_batch do this kind of things

$data = array(
   array(
      'title' => 'My title' ,
      'name' => 'My Name' ,
      'date' => 'My date'
   ),
   array(
      'title' => 'Another title' ,
      'name' => 'Another Name' ,
      'date' => 'Another date'
   )
);

$this->db->insert_batch('mytable', $data); 

// Produces: INSERT INTO mytable (title, name, date) VALUES ('My title', 'My name', 'My date'), ('Another title', 'Another name', 'Another date')

So it would produce only one query with all the values, normally this way faster then doing separate inserts.