Sample StatsD messages when instructed

Bug: T106457
Change-Id: I8ddb5a53dcbaf398f5a114d2a4a862842e980db4

autoload.php

@@ -1058,6 +1058,7 @@ $wgAutoloadLocalClasses = array(
 	'SQLiteField' => __DIR__ . '/includes/db/DatabaseSqlite.php',
 	'SVGMetadataExtractor' => __DIR__ . '/includes/media/SVGMetadataExtractor.php',
 	'SVGReader' => __DIR__ . '/includes/media/SVGMetadataExtractor.php',
+	'SamplingStatsdClient' => __DIR__ . '/includes/libs/SamplingStatsdClient.php',
 	'Sanitizer' => __DIR__ . '/includes/Sanitizer.php',
 	'SavepointPostgres' => __DIR__ . '/includes/db/DatabasePostgres.php',
 	'ScopedCallback' => __DIR__ . '/includes/libs/ScopedCallback.php',

includes/GlobalFunctions.php

@@ -1259,7 +1259,7 @@ function wfLogProfilingData() {
 			$statsdHost = $statsdServer[0];
 			$statsdPort = isset( $statsdServer[1] ) ? $statsdServer[1] : 8125;
 			$statsdSender = new SocketSender( $statsdHost, $statsdPort );
-			$statsdClient = new StatsdClient( $statsdSender, true, false );
+			$statsdClient = new SamplingStatsdClient( $statsdSender, true, false );
 			$statsdClient->send( $context->getStats()->getBuffer() );
 		} catch ( Exception $ex ) {
 			MWExceptionHandler::logException( $ex );

includes/libs/BufferingStatsdDataFactory.php

@@ -20,6 +20,7 @@
  * @file
  */
 
+use Liuggio\StatsdClient\Entity\StatsdData;
 use Liuggio\StatsdClient\Entity\StatsdDataInterface;
 use Liuggio\StatsdClient\Factory\StatsdDataFactory;
 
@@ -75,6 +76,9 @@ class BufferingStatsdDataFactory extends StatsdDataFactory {
 		return $entity;
 	}
 
+	/**
+	 * @return StatsdData[]
+	 */
 	public function getBuffer() {
 		return $this->buffer;
 	}

includes/libs/SamplingStatsdClient.php

@@ -0,0 +1,133 @@
+<?php
+/**
+ * Copyright 2015
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ */
+
+use Liuggio\StatsdClient\StatsdClient;
+use Liuggio\StatsdClient\Entity\StatsdData;
+use Liuggio\StatsdClient\Entity\StatsdDataInterface;
+
+/**
+ * A statsd client that applies the sampling rate to the data items before sending them.
+ *
+ * @since 1.26
+ */
+class SamplingStatsdClient extends StatsdClient {
+	/**
+	 * Sets sampling rate for all items in $data.
+	 * The sample rate specified in a StatsdData entity overrides the sample rate specified here.
+	 *
+	 * {@inheritDoc}
+	 */
+	public function appendSampleRate( $data, $sampleRate = 1 ) {
+		if ( $sampleRate < 1 ) {
+			array_walk( $data, function( $item ) use ( $sampleRate ) {
+				/** @var $item StatsdData */
+				if ( $item->getSampleRate() === 1 ) {
+					$item->setSampleRate( $sampleRate );
+				}
+			});
+		}
+
+		return $data;
+	}
+
+	/**
+	 * Sample the metrics according to their sample rate and send the remaining ones.
+	 *
+	 * {@inheritDoc}
+	 */
+	public function send( $data, $sampleRate = 1 ) {
+		if ( !is_array( $data ) ) {
+			$data = array( $data );
+		}
+		if ( !$data ) {
+			return;
+		}
+		foreach ( $data as $item ) {
+			if ( !( $item instanceof StatsdDataInterface ) ) {
+				throw new InvalidArgumentException(
+					'SamplingStatsdClient does not accept stringified messages' );
+			}
+		}
+
+		// add sampling
+		if ( $sampleRate < 1 ) {
+			$data = $this->appendSampleRate( $data, $sampleRate );
+		}
+		$data = $this->sampleData( $data );
+
+		$messages = array_map( 'strval', $data );
+
+		// reduce number of packets
+		if ( $this->getReducePacket() ) {
+			$data = $this->reduceCount( $data );
+		}
+		//failures in any of this should be silently ignored if ..
+		$written = 0;
+		try {
+			$fp = $this->getSender()->open();
+			if ( !$fp ) {
+				return;
+			}
+			foreach ( $messages as $message ) {
+				$written += $this->getSender()->write( $fp, $message );
+			}
+			$this->getSender()->close( $fp );
+		} catch ( Exception $e ) {
+			$this->throwException( $e );
+		}
+
+		return $written;
+	}
+
+	/**
+	 * Throw away some of the data according to the sample rate.
+	 * @param StatsdDataInterface[] $data
+	 * @return array
+	 * @throws LogicException
+	 */
+	protected function sampleData( $data ) {
+		$newData = array();
+		$mt_rand_max = mt_getrandmax();
+		foreach ( $data as $item ) {
+			$samplingRate = $item->getSampleRate();
+			if ( $samplingRate <= 0.0 || $samplingRate > 1.0 ) {
+				throw new LogicException( 'Sampling rate shall be within ]0, 1]' );
+			}
+			if (
+				$samplingRate === 1 ||
+				( mt_rand() / $mt_rand_max <= $samplingRate )
+			) {
+				$newData[] = $item;
+			}
+		}
+		return $newData;
+	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	protected function throwException( Exception $exception ) {
+		if ( !$this->getFailSilently() ) {
+			throw $exception;
+		}
+	}
+}

tests/phpunit/includes/libs/SamplingStatsdClientTest.php

@@ -0,0 +1,43 @@
+<?php
+
+use Liuggio\StatsdClient\Entity\StatsdData;
+
+class SamplingStatsdClientTest extends PHPUnit_Framework_TestCase {
+	/**
+	 * @dataProvider samplingDataProvider
+	 */
+	public function testSampling( $data, $sampleRate, $seed, $expectWrite ) {
+		$sender = $this->getMock( 'Liuggio\StatsdClient\Sender\SenderInterface' );
+		$sender->expects( $this->any() )->method( 'open' )->will( $this->returnValue( true ) );
+		if ( $expectWrite ) {
+			$sender->expects( $this->once() )->method( 'write' )
+				->with( $this->anything(), $this->equalTo( $data ) );
+		} else {
+			$sender->expects( $this->never() )->method( 'write' );
+		}
+		mt_srand( $seed );
+		$client = new SamplingStatsdClient( $sender );
+		$client->send( $data, $sampleRate );
+	}
+
+	public function samplingDataProvider() {
+		$unsampled = new StatsdData();
+		$unsampled->setKey( 'foo' );
+		$unsampled->setValue( 1 );
+
+		$sampled = new StatsdData();
+		$sampled->setKey( 'foo' );
+		$sampled->setValue( 1 );
+		$sampled->setSampleRate( '0.1' );
+
+		return array(
+			// $data, $sampleRate, $seed, $expectWrite
+			array( $unsampled, 1, 0 /*0.44*/, $unsampled ),
+			array( $sampled, 1, 0 /*0.44*/, null ),
+			array( $sampled, 1, 4 /*0.03*/, $sampled ),
+			array( $unsampled, 0.1, 4 /*0.03*/, $sampled ),
+			array( $sampled, 0.5, 0 /*0.44*/, null ),
+			array( $sampled, 0.5, 4 /*0.03*/, $sampled ),
+		);
+	}
+}