I will show this with my Superleansilexplate and will integrate it there as an example.
Since i dont want to integrate MongoDB in Superleansilexplate it will just become an additional gist.

Given you have some smaller amount of data like a counter that needs to be stored or other loose coupled datasets, we simply speak to MongoDB “directly” and store the data via Doctrine MongoDB Abstraction Layer.
Since i presume the Data / Document Structure isnt that complex we dont use Doctrine MongoDB ODM (the Object Document Mapper).
If you want to use it instead, try this Silex Extensions.

So we use this SilexExtensions collection and install it via git:

 cd mysilexproject
 git clone git@github.com:fate/Silex-Extensions.git vendor/silex-extension

Then we install the doctrine mongodb libary manually:

 git clone --recursive https://github.com/doctrine/mongodb vendor/mongodb

The extension collection has some more poviders but you can just ignore them and just focus on the MongoDbExtension.

– i actually dont like extensions collections. i would prefer to clone each extensions individually. thou its not much code overhead, but when it comes to the vendor dependencies it can become quite messy IMHO –

Alright now the code.
Edit src/app.php and register the namespace for the extension:

 $app['autoloader']->registerNamespace('SilexExtension', __DIR__ . '/../vendor/silex-extension/src');

Then register the MongoDbExtension;

 $app->register(new SilexExtension\MongoDbExtension(), array(
 'mongodb.class_path' => __DIR__ . '/../vendor/mongodb/lib',
 'mongodb.connection' => array(
 'server' => 'mongodb://mysecretuser:mysecretpassw@localhost',
 'options' => array(),
 'eventmanager' => function($eventmanager) {
 }
 )
 ));

and finally query your MongoDB collection of choice and display the resultset as json:

$app->get('/data-from-mongodb', function() use($app) {

$coll = $app['mongodb']->selectDatabase('mydb')->selectCollection('mycoll');
 $query = array(
 'query' => 'value'
 );
 $sort = array(
 'count' => -1,
 );
 $r = $coll->find($query)->sort($sort)->toArray();
 $response = new Response();
 $response->headers->set('Content-type', 'application/json');
 $response->setContent(json_encode($r));
 return $response;
 });

Easy

Cannot allocate memory at ...

So first i suspected mongodb to use up loads of memory as top showed.

But after some recherche work i learned mongodb only -seems- to use a lot of memory.
see here and here and here
The actual usage was around 20mb RAM, so mongodb was innocent.

The true RAM monsters were some apache and php-fpm zombies, but thats another story.

While suspecting mongodb i thought about outsourcing the mongodb and i found a free and sufficient offer in mongolab.
My interests were on and i gave it a try.
The free version has a limit for up to 240MB storage and since my app is just a small counter it should last for some time.

The registration was easy, creation of the database aswell and the administration panel is also pretty cool and informative.

Then create a user and migrate:

First get my data from the vserver on the vserver:

 mongodump --host 127.0.0.1

Then fetch it to my local machine:

 scp -r me@vserver.de:/var/www/vhosts/verrueckte/dump/mongodumpdata .

Ups i didnt had no mongo client on my local machine, go get it:

 sudo apt-get install mongodb-clients

Now connect to the mongolab via your console

 mongo db123xyz.mongolab.com:12345/thedb -u <user> -p <pw>

Hey works, great!
Alright see you later.

 > exit;

Now import the dumps to continue the counter there were i stopped.

 cd mongodumpdata
 mongorestore -h db123xyz.mongolab.com:12345 -d thedb -u -p .

Good!

Then teach the php app the new connection:

 $this->host = 'mongodb://user:pw@db123xyz.mongolab.com:12345/thedb';
 new mongo($this->host);

There you go! The counter is storing its stuff to the mongolab database.
And i can stop the mongod on my machine and free some memory.

 ps aux | grep mongodb
 kill <PID>

MongoDb hat zwar eine group() function, die in etwa SQLs GROUP BY entspricht, allerdings kann man dies nicht kombinieren mit SORT oder LIMIT bzw den sort() und limit() Funktionen, da diese keinen Cursor zurückgibt sondern direkt ein Array.

Will man also sortieren und limitieren muss man sich des Map / Reduce features von MongoDB bedienen.

Ein Query wie folgt:

SELECT referer.URL, count(*) AS cnt
FROM `referer`
GROUP BY referer.URL
ORDER BY cnt ASC LIMIT 25

…wird dann über Command() so umgesetzt:

$map = new MongoCode("function() { emit(this.url,1); }");
$reduce = new MongoCode("function(k, vals) { ".
			"var sum = 0;".
			"for (var i in vals) {".
			"sum += vals[i];". 
			"}".
			"return sum; }");
$r = $this->db_handler->command(array(
		    	"mapreduce" => "referer", 
		    	"map" => $map,
		    	"reduce" => $reduce));
$r = $this->db_handler->selectCollection($r['result'])->find();
$r->sort(array('value' => -1));
$r->limit(25);
$data = array();
foreach ($r as $ref) {
	$data[$ref['_id']] = $ref['value'];
}
return $data;

In die Reduce Funktion kann man sämtliche Abfrage-Logik packen, was es zu einem ziemlich mächtigem Konstrukt macht.
Hat man sich einmal dran gewöhnt, lässt sich eine Menge damit anstellen.

Danke auch an diesen Blog.