# PHP Memcached
PHP Sessions don't work on clusters, memcached provides a solution.
The procedure is as follows:

```
create a new Memcached object
call memcached::addServer
retrieve the value with memcached::get
if the value was retrieved successfully
  carry on
else
  store the value with memcached::set
  ```
  
* When the page is first loaded, the value will not be found in the cache (obviously), so we need to store it.
* When the page is loaded subsequently the value should be found, the program can proceed normally.
* There is a timeout, after which time the value will be removed. Many memcached members have a default parameter
to set your own timeout. This is a hint only.

From Wikipedia:
>"Memcached's APIs provide a very large hash table distributed across multiple machines. When the table is full, 
>subsequent inserts cause older data to be purged in least recently used (LRU) order. Applications using 
>Memcached typically layer requests and additions into RAM before falling back on a slower backing store, such 
>as a database".


## A little experiment
The first time round the value is not found, so we store it. Subsequently it is retrieved successfully.
We can reset by adding ?reset=1 to the uri.
```
// reset
if (isset($_GET['reset'])) {
  echo "Deleting cached value";
  $cache->delete('testValue');
  echo "Result is " . $cache->getResultMessage();
  exit();
}

// Try to retrieve the cached value
$cachedValue = $cache->get('testValue');

if ($cachedValue) {                                            // we got the value
  echo "Value successfully retrieved: $cachedValue ";
} else {                                                      // value not found, so store it
  echo "failed to retreive testvalue, so setting testvalue";
  $cache->set('testValue', 12345);
}

echo "Result was " . $cache->getResultMessage();
```

## Profiler results
```
constructor  0.5
addServer    0.5
set         21.5
get         57.7
```