How can i make my 3 level hierarchy load fast

Question

Here's how I'm getting my data from database. It is a 3 level hierarchy. Parent, child and children of child.

page_id | parent_id 
    1         0          
    2         1
    3         0
    4         3

The top data shows 0 as the parent.

$id = 0;
public function getHierarchy($id)
   {
       $Pages = new Pages();
       $arr = array();
       $result = $Pages->getParent($id);

       foreach($result as $p){
           $arr[] = array(
               'title' => $p['title'],
               'children' => $this->getHierarchy($p['page_id']),
               );
       }
       return $arr;
   } 

So far I'm getting data but it's kinda slow. The browser loads so long before showing the data. How can I make my code faster so it does not take long for the browser to load data?

Thanks.

Answer 1

You have multiple options to speed it up:

1. Select all rows from table and do the recursion only on the PHP side. It's only an option if there are not too many rows in table.
2. You can self join the table. This is a nice option if you know that there are no more levels of hierarchy in the future. Look at the post: http://blog.richardknop.com/2009/05/adjacency-list-model/
3. Use nested sets: http://en.wikipedia.org/wiki/Nested_set_model
4. Or my favorite: Closure Table
5. Use some kind of caching. You could cache the db queries or the whole tree menu html or the PHP array for example.

Caching example:

Caching you can do in normal files or use specialized api's like memcache, memcached or apc. Usually you have a class with 3 basic methods. An interface could look like:

interface ICache
{
    public function get($key);
    public function set($key, $value, $lifetime = false);
    public function delete($key);
}

You can use it like:

public function getHierarchy($id)
{
    $cached = $this->cache->get($id);
    if (false !== $cached) {
        return $cached;
    }

    // run another method where you build the tree ($arr)

    $this->cache->set($id, $arr, 3600);

    return $arr;
}

In the example the tree will be cached for one hour. You also could set unlimited lifetime and delete the key if you insert another item to the db.