# Metrics The driver exposes measurements of its internal behavior through the popular [Dropwizard Metrics](http://metrics.dropwizard.io/3.2.2/manual/index.html) library. Developers can access these metrics and choose to export them to a monitoring tool. The driver depends on Metrics 3.2.x, but is compatible with newer versions of Dropwizard Metrics. For using Metrics 4.x with the driver, see [Metrics 4 Compatibility](). ## Structure Metric names are path-like, dot-separated strings. Metrics are measured at the `Cluster`-level, thus the driver prefixes them with the name of the `Cluster` they are associated with (see [withClusterName](https://java-driver.docs.scylladb.com/scylla-3.12.1.x/api/com/datastax/driver/core/Cluster.Builder.html#withClusterName-java.lang.String-) for how to configure this), suffixed by `-metrics`. For example: ```default cluster1-metrics.connected-to cluster1-metrics.connection-errors ... ``` ## Configuration By default, metrics are enabled and exposed via JMX as [MXBeans](https://docs.oracle.com/javase/tutorial/jmx/mbeans/mxbeans.html). Some users may find that they don’t want the driver to record and expose metrics. To disable metrics collection, use the [withoutMetrics](https://java-driver.docs.scylladb.com/scylla-3.12.1.x/api/com/datastax/driver/core/Cluster.Builder.html#withoutMetrics--) builder method, i.e.: ```java Cluster cluster = Cluster.builder() .withoutMetrics() .build(); ``` Note that if you decide to disable metrics, you may also consider excluding metrics as a dependency. To do this in a maven project: ```xml com.scylladb scylla-driver-core 3.11.5.0 io.dropwizard.metrics metrics-core ``` Alternatively, one may not want to expose metrics using JMX. Disabling JMX reporting is simple as using the [withoutJMXReporting](https://java-driver.docs.scylladb.com/scylla-3.12.1.x/api/com/datastax/driver/core/Cluster.Builder.html#withoutJMXReporting--) builder method, i.e.: ```java Cluster cluster = Cluster.builder() .withoutJMXReporting() .build(); ``` ## Accessing Cluster Metrics `Cluster` metrics may be accessed via the [getMetrics](https://java-driver.docs.scylladb.com/scylla-3.12.1.x/api/com/datastax/driver/core/Cluster.html#getMetrics--) method. The [Metrics](https://java-driver.docs.scylladb.com/scylla-3.12.1.x/api/com/datastax/driver/core/Metrics.html) class offers direct access to all metrics recorded for the `Cluster` via getter methods. Refer to the [Metrics javadoc](https://java-driver.docs.scylladb.com/scylla-3.12.1.x/api/com/datastax/driver/core/Metrics.html) for more details about the metrics offered. It is very common for applications to record their own metrics. You can add all metrics recorded for a `Cluster` to your applications’ [MetricRegistry](http://metrics.dropwizard.io/3.2.2/apidocs/com/codahale/metrics/MetricRegistry.html) in the following manner: ```java MetricRegistry myRegistery = new MetricRegistry(); myRegistry.registerAll(cluster.getMetrics().getRegistry()); ``` ## Registering a Custom Reporter Dropwizard Metrics offers a variety of [Reporters](http://metrics.dropwizard.io/3.2.2/manual/core.html#reporters) for exporting metrics. To enable reporting, access the `Cluster`’s metrics via the [getMetrics](https://java-driver.docs.scylladb.com/scylla-3.12.1.x/api/com/datastax/driver/core/Cluster.html#getMetrics--) method. For example, to enable CSV reporting every 30 seconds: ```java import com.codahale.metrics.*; import java.io.File; import java.util.concurrent.TimeUnit; Metrics metrics = cluster.getMetrics(); CsvReporter csvReporter = CsvReporter.forRegistry(metrics.getRegistry()) .convertDurationsTo(TimeUnit.MILLISECONDS) .convertRatesTo(TimeUnit.SECONDS) .build(new File(".")); csvReporter.start(30, TimeUnit.SECONDS); ``` ## Metrics 4 Compatibility While the driver depends on Metrics 3.2.x, it also works with Metrics 4, with some caveats. In Metrics 4, JMX reporting was moved to a separate module, `metrics-jmx`. Because of this you are likely to encounter the following exception at runtime when initializing a `Cluster`: ```default Exception in thread "main" java.lang.NoClassDefFoundError: com/codahale/metrics/JmxReporter at com.datastax.driver.core.Metrics.(Metrics.java:103) at com.datastax.driver.core.Cluster$Manager.init(Cluster.java:1402) at com.datastax.driver.core.Cluster.init(Cluster.java:159) at com.datastax.driver.core.Cluster.connectAsync(Cluster.java:330) at com.datastax.driver.core.Cluster.connectAsync(Cluster.java:305) at com.datastax.durationtest.core.DurationTest.createSessions(DurationTest.java:360) .... Caused by: java.lang.ClassNotFoundException: com.codahale.metrics.JmxReporter at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582) at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:185) at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:496) ... 8 more ``` To fix this, use [withoutJMXReporting](https://java-driver.docs.scylladb.com/scylla-3.12.1.x/api/com/datastax/driver/core/Cluster.Builder.html#withoutJMXReporting--) when constructing your `Cluster`. If you still desire JMX reporting, add `metrics-jmx` as a dependency: ```xml io.dropwizard.metrics metrics-jmx 4.0.2 ``` Then create your `Cluster` and `JmxReporter` in the following manner: ```java Cluster cluster = Cluster.builder() .withoutJMXReporting() .build(); JmxReporter reporter = JmxReporter.forRegistry(cluster.getMetrics().getRegistry()) .inDomain(cluster.getClusterName() + "-metrics") .build(); reporter.start(); ```