Enabling caching .

Caching is enabled in three step.
1) Create a writable directory on your server where you want strored the cache files.
2) Set the path to your cache folder in your application/config/database.php file.
3) Enable the caching feature, either globally by setting the preference in your application/config/database.php file.
Important Note: This class is initialized automatically by the database driver when caching is enabled. Do NOT load this class manually.

References functions.

$this->db->cache_on()  /   $this->db->cache_off()
// Turn caching on
$this->db->cache_on();
$query = $this->db->query("SELECT * FROM mytable");

// Turn caching off for this one query
$this->db->cache_off();
$query = $this->db->query("SELECT * FROM members WHERE member_id = '$current_user'");

// Turn caching back on
$this->db->cache_on();
$query = $this->db->query("SELECT * FROM another_table");

Delete caching files.
Deletes the cache files associated with a particular page. This is useful if you need to clear caching after you update your database.

$this->db->cache_delete();
$this->db->cache_delete('blog', 'comments');
$this->db->cache_delete_all();