This project contains modifications to the dropwizard metrics project.
The primary additions includes a replacement for MetricRegistry allowing for
metric names containing tags through
MetricId.
The following are the interfaces and classes that has to be used from this package in order for MetricId to be used.
You will find these types in com.spotify.metrics.core.
- SemanticMetricRegistry — Replacement for MetricRegistry.
- MetricId — Replacement for string-based metric names.
- SemanticMetricFilter — Replacement for MetricFilter.
- SemanticMetricRegistryListener — Replacement for MetricRegistryListener.
- SemanticMetricSet — Replacement for MetricSet.
Care must be taken not to use the upstream MetricRegistry because it does not
support the use of MetricId.
To ease this, all of the replacing classes follow the Semantic* naming
convention.
As an effect of this, pre-existing plugins for codahale metrics will not work.
Add a dependency in maven.
<dependency>
<groupId>com.spotify.metrics</groupId>
<artifactId>semantic-metrics-core</artifactId>
<version>0.2.3</version>
</dependency>
This project provide the following set of plugins;
- com.spotify.metrics.ffwd A reporter into FastForward.
- com.spotify.metrics.jvm Ported MetricSet's for internal java statistics.
See and run examples.
If you find yourself in a situation where you create many instances of this class (i.e. when reporting metrics), make use of MetricIdCache
The following is an example integrating with Guava.
// GuavaCache.java
public final class GuavaCache<T> implements MetricIdCache.Cache<T> {
final Cache<T, MetricId> cache = CacheBuilder.newBuilder().expireAfterAccess(6, TimeUnit.HOURS)
.build();
private final MetricIdCache.Loader<T> loader;
public GuavaCache(Loader<T> loader) {
this.loader = loader;
}
@Override
public MetricId get(final MetricId base, final T key) throws ExecutionException {
return cache.get(key, new Callable<MetricId>() {
@Override
public MetricId call() throws Exception {
return loader.load(base, key);
}
});
}
@Override
public void invalidate(T key) {
cache.invalidate(key);
}
@Override
public void invalidateAll() {
cache.invalidateAll();
}
public static MetricIdCache.Any setup() {
return MetricIdCache.builder().cacheBuilder(new MetricIdCache.CacheBuilder() {
@Override
public <T> MetricIdCache.Cache<T> build(final Loader<T> loader) {
return new GuavaCache<T>(loader);
}
});
}
}// MyApplicationStatistics.java
public class MyApplicationStatistics() {
private final MetricIdCache.Typed<String> endpoint = GuavaCache.setup()
.loader(new MetricIdCache.Loader<String>() {
@Override
public MetricId load(MetricId base, String endpoint) {
return base.tagged("endpoint", endpoint);
}
});
private final MetricIdCache<String> requests = endpoint
.metricId(MetricId.build().tagged("what", "endpoint-requests", "unit", "request"))
.build();
private final MetricIdCache<String> errors = endpoint
.metricId(MetricId.build().tagged("what", "endpoint-errors", "unit", "error"))
.build();
private final SemanticMetricRegistry registry;
public MyApplicationStatistics(SemanticMetricRegistry registry) {
this.registry = registry;
}
public void reportRequest(String endpoint) {
registry.meter(requests.get(endpoint)).mark();
}
public void reportError(String endpoint) {
registry.meter(errors.get(endpoint)).mark();
}
}Avoid performing deep integration of semantic-metrics into your library or application. This will prevent you, and third parties, from integrating your code with different metric collectors.
As an alternative you should build a tree of interfaces that your application
uses to report metrics (e.g. my-service-statistics), and use these to
build an implementation using semantic metrics
(my-service-semantic-statistics).
This pattern greatly simplifes integrating your application with more than one metric collector, or ditching semantic-metrics when it becomes superseded by something better.
At configuration time your application can decide which implementation to use by simply providing an instance of the statistics API which suits their requirements.
Build an interface describing all the things that your application reports.
public interface MyApplicationStatistics {
/**
* Report that a single request has been received by the application.
*/
void reportRequest();
}Provide a semantic-metrics implementation.
public class SemanticMyApplicationStatistics implements MyApplicationStatistics {
private final SemanticMetricRegistry registry;
private final Meter request;
public SemanticMyApplicationStatistics(SemanticMetricRegistry registry) {
this.registry = registry;
this.request = registry.meter(MetricId.build().tagged(
"what", "requests", "unit", "request"));
}
@Override
public void reportRequest() {
request.mark();
}
}Now a user of your framework/application can do something like the following to bootstrap your application.
public class Entry {
public static void main(String[] argv) {
final SemanticMetricRegistry registry = new SemanticMetricRegistry();
final MyApplicationStatistics statistics = new SemanticMyApplicationStatistics(registry);
/* your application */
final MyApplication app = MyApplication.builder().statistics(statistics).build();
final FastForwardReporter reporter = FastForwardReporter.forRegistry(registry).build()
reporter.start();
app.start();
app.join();
System.exit(0);
}
}There are different metric types that can be used depending on what it is that we want to measure, e.g., queue length, or request time, etc.
A gauge is an instantaneous measurement of a value. For example of we want to measure the number of pending jobs in a queue.
registry.register(metric.tagged("what", "job-queue-length"), new Gauge<Integer>() {
@Override
public Integer getValue() {
// fetch the queue length the way you like
final int queueLength = 10;
// obviously this is gonna keep reporting 10, but you know ;)
return queueLength;
}
});A counter is just a gauge for an AtomicLong instance. You can increment or decrement its value.
For example we want a more efficient way of measuring the pending job in a queue.
final Counter counter = registry.counter(metric.tagged("what", "job-count"));
// Somewhere in your code where you are adding new jobs to the queue you increment the counter as well
counter.inc();
// Somewhere in your code the job is going to be removed from the queue you decrement the counter
counter.dec();A meter measures the rate of events over time (e.g., "requests per second"). In addition to the mean rate, meters also track 1-, 5-, and 15-minute moving averages.
For example we have an endpoint that we want to measure how frequent we receive requests for it.
Meter meter = registry.meter(metric.tagged("what", "incoming-requests").tagged("endpoint", "/v1/list"));
// Now a request comes and it's time to mark the meter
meter.mark();A histogram measures the statistical distribution of values in a stream of data. In addition to minimum, maximum, mean, etc., it also measures median, 75th, 90th, 95th, 98th, 99th, and 99.9th percentiles.
For example this histogram will measure the size of responses in bytes.
Histogram histogram = registry.histogram(metric.tagged("what", "response-size").tagged("endpoint", "/v1/content"));
// fetch the size of the response
final long responseSize = getResponseSize(response);
histogram.update(responseSize);A timer measures both the rate that a particular piece of code is called and the distribution of its duration.
For example we want to measure the rate and handling duration of incoming requests.
Timer timer = registry.timer(metric.tagged("what", "incoming-request-time").tagged("endpoint", "/v1/get_stuff"));
// Do this before starting to do the thing. This creates a measurement context object that you can pass around.
final Context context = timer.time();
doStuff();
// Tell the context that it's done. This will register the duration and counts one occurrence.
context.stop();When dealing with thousands of similar timeseries over thousands of hosts, classification becomes a big issue.
Classical systems organize metric names as strings, containing a lot of information about the metric in question.
You will often see things like webserver.host.example.com.df.used./.
The same metric expressed as a set of tags could look like.
{"role": "webserver", "host": "host.example.com", "what": "disk-used",
"mountpoint": "/"}This system of classification from the host machine greatly simplifies any metrics pipeline. When transported with a stable serialization method (like JSON) it does not matter if we add additional tags, or decide to change the order in which the timeserie happens to be designated.
We can also easily index this timeseries by it's tag using a system like ElasticSearch and ask it interesting questions about which timeseries are available.
If used with a metrics backend that supports efficient aggregation and filtering across tags you gain a flexible and intionistic pipeline that is powerful and agnostic about what it sends, all the way from the service being monitored to your metrics GUI.
This project adheres to the Open Code of Conduct. By participating, you are expected to honor this code.
- Fork semantic-metrics from github and clone your fork.
- Hack.
- Push the branch back to GitHub.
- Send a pull request to our upstream repo.