Application Performance Monitoring (APM)
Since version 1.3, the MongoDB driver contains an API for performance
monitoring. This API allows you to find out how long specific operations
take by setting up subscribers. Each subscriber is required to implement one
or more interfaces under the MongoDB\Driver\Monitoring
namespace. Currently, only the
MongoDB\Driver\Monitoring\CommandSubscriber interface
is available.
The MongoDB\Driver\Monitoring\CommandSubscriber
interface defines three methods: commandStarted,
commandSucceeded, and commandFailed.
Each of these three methods accept a single event
argument of a specific class for the respective event. For example, the
commandSucceeded's $event argument
is a MongoDB\Driver\Monitoring\CommandSucceededEvent
object.
In this tutorial we will implement a subscriber that creates a list of all
the query profiles and the average time they took.
Subscriber Class Scaffolding
We start with the framework for our subscriber:
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Registering the Subscriber
Once a subscriber object is instantiated, it needs to be registered with the
driver's monitoring system. This is done by calling
MongoDB\Driver\Monitoring\addSubscriber.
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Implementing the Logic
With the object registered, the only thing left is to implement the logic
in the subscriber class. To correlate the two events that make up a
successfully executed command (commandStarted and commandSucceeded), each
event object exposes a requestId field.
To record the average time per query shape, we will start by checking for a
find command in the commandStarted event. We will then add
an item to the pendingCommands property indexed by its
requestId and with its value representing the query shape.
If we receive a corresponding commandSucceeded event with the same
requestId, we add the duration of the event (from
durationMicros) to the total time and increment the
operation count.
If a corresponding commandFailed event is encountered, we just remove the
entry from the pendingCommands property.
getCommand() ) )
{
$queryShape = $this->createQueryShape( (array) $event->getCommand()->filter );
$this->pendingCommands[$event->getRequestId()] = $queryShape;
}
}
public function commandSucceeded( \MongoDB\Driver\Monitoring\CommandSucceededEvent $event )
{
$requestId = $event->getRequestId();
if ( array_key_exists( $requestId, $this->pendingCommands ) )
{
$this->queryShapeStats[$this->pendingCommands[$requestId]]['count']++;
$this->queryShapeStats[$this->pendingCommands[$requestId]]['duration'] += $event->getDurationMicros();
unset( $this->pendingCommands[$requestId] );
}
}
public function commandFailed( \MongoDB\Driver\Monitoring\CommandFailedEvent $event )
{
if ( array_key_exists( $event->getRequestId(), $this->pendingCommands ) )
{
unset( $this->pendingCommands[$event->getRequestId()] );
}
}
public function __destruct()
{
foreach( $this->queryShapeStats as $shape => $stats )
{
echo "Shape: ", $shape, " (", $stats['count'], ")\n ",
$stats['duration'] / $stats['count'], "µs\n\n";
}
}
}
$m = new \MongoDB\Driver\Manager( 'mongodb://localhost:27016' );
/* Add the subscriber */
\MongoDB\Driver\Monitoring\addSubscriber( new QueryTimeCollector() );
/* Do a bunch of queries */
$query = new \MongoDB\Driver\Query( [
'region_slug' => 'scotland-highlands', 'age' => [ '$gte' => 20 ]
] );
$cursor = $m->executeQuery( 'dramio.whisky', $query );
$query = new \MongoDB\Driver\Query( [
'region_slug' => 'scotland-lowlands', 'age' => [ '$gte' => 15 ]
] );
$cursor = $m->executeQuery( 'dramio.whisky', $query );
$query = new \MongoDB\Driver\Query( [ 'region_slug' => 'scotland-lowlands' ] );
$cursor = $m->executeQuery( 'dramio.whisky', $query );
?>
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