Inefficient Query for comments in cron job

There's a job that runs every hour for you to fetch comments from facebook and import them. This can take up to 19 seconds on m server (a well powered 8GB/8CPU machine). I'm looking for ways to improve its speed. Please share any suggestions.

Also, I noticed that in the below function, you aren't using meta_key in the where statement. My commentmeta table has over 116,000 entries and it has to do a full table scan. Adding in meta_key allows it to use the meta_key index at least. Can you look into it and see if it needs updating?

function comment_already_imported( $fb_cid ) {
if ( ! $fb_cid ) {
return false;
}
$key = '%s:13:"fb_comment_id";s:' . strlen( $fb_cid ) . ':"' . $fb_cid . '";%';
$sql = "SELECT meta_id, comment_id FROM " . $this->db->prefix . "commentmeta WHERE meta_value LIKE '{$key}'";

return $this->db->get_row( $sql );
}