How to speedup codeigniter/php pagination, sql-query

Question

EDIT: usr_id, cat_ids, active, id_1, id_2, id_3 => INDEXED. And of course all id are primary key Here is my SQL tables, and the query I'm making with codeigniter:

function getAllPosts($limit = 0, $start = 0)
{
    $data = $this->db->select('p.*, u.nickname, u.usr_status, u.usr_rating, pc.*, c1.category as category_1, c2.category as category_2, c3.category as category_3')
                 ->from('posts p')
                 ->join('users u', 'p.usr_id = u.id', 'inner')
                 ->join('post_categories pc', 'p.cat_ids = pc.id', 'inner')
                 ->join('categories c1', 'pc.id_1 = c1.id', 'inner')
                 ->join('categories c2', 'pc.id_2 = c2.id', 'left')
                 ->join('categories c3', 'pc.id_3 = c3.id', 'left')
                 ->limit($limit, $start)
                 ->order_by('p.id', 'desc')
                 ->where('p.active', 1)
                 ->get()
                 ->result_array();

also controller:

    $config['base_url']         = base_url() . 'posts/'. $base_url;
    $config['total_rows']       = $this->db->count_all('posts');
    $config['per_page']         = 10;
    $config['num_links']        = 5;
    $config['use_page_numbers'] = TRUE;
    $config['uri_segment']      = 3;
    $this->pagination->initialize($config);
    $page = $this->uri->segment(3);
    $data['posts'] = $this->m_posts->getAllPosts($config['per_page'], $page);
    $data['pagination'] = $this->pagination->create_links();

So how can I speed up all this pagination stuff... because when there's 1,5k pages (15000 posts) it slows all down... I guess all info I could, I gave but be free to ask for some more info

Answer 1

You can get a more especific optimization tip by running an explain query from you tables.

http://dev.mysql.com/doc/refman/5.0/en/using-explain.html

It identifies where you can add indexes (and what kinf of indexes) to a better performance tunning.

More pratic information can be found here: http://www.sitepoint.com/using-explain-to-write-better-mysql-queries/

Hope it helps!