how to get the count of total comments posted for specific content type including deleted comments too? I want to get the total count of comments posted only for a specific content type including deleted to get the highest comment id no matter whether comment is been deleted. please help me or else suggest me other way to achieve this.
You can always dig around the database with a db query with something like:

$content_type = 'mycontenttype';
$query = db_select('comment', 'c');

$query-&gt;join('node', 'n', 'n.nid = c.nid'); //JOIN node with comment
$query-&gt;fields('c', array('cid')); //SELECT the fields from comment
$query-&gt;condition('n.type', $content_type, '=');
$query-&gt;orderBy('c.cid', 'DESC'); //ORDER BY comment id

$num_comments = $query-&gt;countQuery()-&gt;execute()-&gt;fetchField();
$latest_comment_cid = $query-&gt;execute()-&gt;fetchField();


EDIT
In this example I assume you mean unpublished comments and not deleted. See Anil's answer if you want to track count of deleted comments as well.