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HistogramMetric.php
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HistogramMetric.php
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<?php
/**
* 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
*/
declare( strict_types=1 );
namespace Wikimedia\Stats\Metrics;
use InvalidArgumentException;
use Wikimedia\Stats\StatsFactory;
/**
* Histogram Metric Implementation
*
* Histogram Metrics are a collection of CounterMetric arranged into buckets.
*
* @author Cole White
* @since 1.44
*/
class HistogramMetric {
/** @var int Maximum number of allowed buckets. */
private const MAX_BUCKETS = 10;
private StatsFactory $statsFactory;
private string $name;
private array $buckets;
private array $labels = [];
public function __construct( StatsFactory $statsFactory, string $name, array $buckets ) {
$this->statsFactory = $statsFactory;
$this->name = $name;
if ( !$buckets ) {
throw new InvalidArgumentException( 'Stats: Histogram buckets cannot be an empty array.' );
}
$bucketCount = count( $buckets );
if ( $bucketCount > self::MAX_BUCKETS ) {
throw new InvalidArgumentException(
"Stats: Too many buckets defined. Got:{$bucketCount}, Max:" . self::MAX_BUCKETS
);
}
foreach ( $buckets as $bucket ) {
if ( !( is_float( $bucket ) || is_int( $bucket ) ) ) {
throw new InvalidArgumentException( 'Stats: Histogram buckets can only be float or int.' );
}
}
$normalizedBuckets = array_unique( $buckets );
sort( $normalizedBuckets, SORT_NUMERIC );
if ( $buckets !== $normalizedBuckets ) {
throw new InvalidArgumentException(
'Stats: Histogram buckets must be unique and in order of least to greatest.'
);
}
$this->buckets = $buckets;
}
/**
* Ensure every bucket has 0 as the first sample so that it is
* emitted for the exporter to report.
*/
private function preloadBuckets( CounterMetric $metric ): void {
$metric->setBucket( '+Inf' );
$metric->incrementBy( 0 );
foreach ( $this->buckets as $bucket ) {
$metric->setBucket( $bucket );
$metric->incrementBy( 0 );
}
}
/**
* Increments bucket associated with the provided value.
*/
public function observe( float $value ): void {
$count = $this->statsFactory->getCounter( "{$this->name}_count" );
$bucket = $this->statsFactory->getCounter( "{$this->name}_bucket" );
$sum = $this->statsFactory->getCounter( "{$this->name}_sum" );
foreach ( $this->labels as $k => $v ) {
$count->setLabel( $k, $v );
$bucket->setLabel( $k, $v );
$sum->setLabel( $k, $v );
}
if ( $bucket->getSampleCount() === 0 ) {
$this->preloadBuckets( $bucket );
}
$bucket->setBucket( '+Inf' )->increment();
foreach ( $this->buckets as $le ) {
if ( $value <= $le ) {
$bucket->setBucket( $le )->increment();
}
}
$count->increment();
$sum->incrementBy( $value );
}
/**
* Adds a label $key with $value. No order is respected.
*
* @return HistogramMetric
*/
public function setLabel( string $key, string $value ): self {
// each metric will run its own validation logic
$this->labels[$key] = $value;
return $this;
}
/**
* Returns metric with cleared labels.
*
* @return HistogramMetric
*/
public function fresh(): self {
$this->labels = [];
return $this;
}
}

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HistogramMetric.php (3 KB)

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