A Prometheus-compliant Java client, exposing all metric types: Counter, Gauge, Summary and Histogram.
This is not the official Prometheus client, which can be found here: https://github.com/prometheus/client_java
When we began migrating to Prometheus, the support for labels was needed - so we went to check the official client.
At Outbrain metrics are heavily used in all our micro-services and in a multi-threaded environment. Thread-safety is key and the performance impact of using metrics must be negligible.
When reviewing the official Prometheus client we discovered a several synchronized blocks that in the Summary and Gauge metric types. In order to avoid the contention we decided to write our own client, wrapping HdrHistogram and dropwizard-metrics internally, with a custom Bucket-based Histogram implementation.
prometheus-client is hosted on Bintray
Add a maven/gradle dependency:
Maven
<dependency>
<groupId>com.outbrain.swinfra</groupId>
<artifactId>prometheus-client</artifactId>
<version>0.x</version>
</dependency>Gradle
com.outbrain.swinfra:prometheus-client:0.x
All metrics should be stored inside a MetricRegistry. The registry is a collection that contains all of your metric objects and performs validation that no two metrics exist with the same name.
MetricRegistry registry = new MetricRegistry();//No labels
Counter counter = registry.getOrRegister(new CounterBuilder("name", "help").build());
counter.inc();
//With labels
Counter counter = registry.getOrRegister(new CounterBuilder("name", "help").withLabels("label1")
.build());
counter.inc("value1");The gauge takes after the DropWizard's gauge in the sense that it uses a supplier for its value. This is a gauge that always returns the value "1".
Note that for gauges the label values are determined statically.
//No labels
registry.getOrRegister(new GaugeBuilder("name", "help").withValueSupplier(() -> 1d).build());
//With labels
registry.getOrRegister(new GaugeBuilder("name", "help").withLabels("label1")
.withValueSupplier(() -> 1d, "value1")
.build());A gauge whose value is set from an outside source, along with the label values if relevant. This is different from the regular gauge where the label values are set statically.
//No labels
SettableGauge settableGauge = registry.getOrRegister(new SettableGaugeBuilder("name", "help")
.build());
settableGauge.set(5);
//With labels
SettableGauge settableGauge = registry.getOrRegister(new SettableGaugeBuilder("name", "help")
.withLabels("label1")
.build());
settableGauge.set(5, "value1");//No labels
Summary summary = registry.getOrRegister(new SummaryBuilder(NAME, HELP).build());
summary.observe(10);
//With labels
Summary summary = registry.getOrRegister(new SummaryBuilder(NAME, HELP).withLabels("label1")
.build());
summary.observe(10, "value1");//No labels
Histogram histogram = registry.getOrRegister(new HistogramBuilder(NAME, HELP).build());
histogram.observe(10);
//With labels
Histogram histogram = registry.getOrRegister(new HistogramBuilder(NAME, HELP).withLabels("label1")
.build());
histogram.observe(10, "value1");//A Summary timer
Summary summaryTimer = registry.getOrRegister(new SummaryBuilder(NAME, HELP).build());
Timer timer = summaeryTimer.startTimer();
//run some code
timer.stop();
//A Histogram timer
Summary histTimer = registry.getOrRegister(new HistogramBuilder(NAME, HELP).build());
Timer timer = histTimer.startTimer();
//run some code
timer.stop();Prometheus uses the Collector class to allow a process to expose its metrics. This client implements a Prometheus Collector that serves exactly this purpose. The MetricCollector class is instantiated with a MetricRegistry.
//Create a MetricCollector and pass your *MetricRegistry* to it
MetricCollector collector = new MetricCollector(registry);
//The collector may be registered in the Prometheus CollectorRegistry
CollectorRegistry.defaultRegistry.register(collector);
//The default registry can then be exposed using Prometheus' MetricsServlet for exampleregistry.getOrRegister(new GaugeBuilder("name", "help").withLabels("label1")
.withValueSupplier(() -> 1, "value1")
.withValueSupplier(() -> 2, "value2")
.build());Summary supports different precisions.
Summary summary = registry.getOrRegister(new SummaryBuilder("name", "help")
.withNumberOfSignificantValueDigits(3)
.build());Histogram can be configured with custom buckets or with equal width buckets at a given range.
//Custom buckets
Histogram histo = registry.getOrRegister(new HistogramBuilder("name", "help")
.withBuckets(0.1, 0.2, 0.5, 1.0)
.build());
//Equal width buckets - creating five buckets with the width 0.2 and starting with 0.1
// 0.1, 0.3, 0.5, 0.7, 0.9
Histogram histo = registry.getOrRegister(new HistogramBuilder("name", "help").withEqualWidthBuckets(0.1, 0.2, 5)
.build());Timer supports custom clocks, with the default being the system clock which measures intervals according to System.nanoTime().
This example shows a timer over a Histogram metric, but it's also applicable to the Summary metric
//Using an instance of MyClock instead of the default
Histogram timer = registry.getOrRegister(new HistogramBuilder("name", "help")
.withClock(new MyClock())
.build()); prometheus-client is released under version 2.0 of the Apache License.
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