Metrics

Being a regular Spring Boot 2+ application, the FactCast Server uses micrometer.io as its metrics emitting/collecting solution. In order to get started collecting the metrics FactCast Server emits, you’ll need to choose a backend/store for your metrics. Micrometer has lots of prebuilt bindings to choose from. Please refer to the respective documentation in the Setup section of the micrometer docs.

When it comes to metrics, you’ll have to know what you’re looking for. There are

• Server metrics in FactCast Server as well as
• Client metrics in the factcast client and additionally in the
• factus client library.

We’re focussing on Server metrics here.

Metric namespaces and their organization

At the time of writing, there are six namespaces exposed:

• factcast.server.timer
• factcast.server.meter
• factcast.store.timer
• factcast.ui.timer
• factcast.store.meter
• factcast.registry.timer
• factcast.registry.meter

Depending on your micrometer binding, you may see a slightly different spelling in your data (like ' factcast_store_timer`, if your datasource has a special meaning for the ‘.’-character)

Furthermore, metrics in operations are automatically tagged with

• an operation name
• a store name (‘pgsql’ currently) and
• an exception tag (‘None’ if unset).

Existing metrics

There are a bunch of metrics already emitted in the server. These metrics can be grouped by type:

• Timers (collecting durations of code execution)
• Meters (collecting metric events, for example, occurrences of errors)

As this list is continuously growing, we cannot guarantee the documentation’s completeness. If you want to see the current list of operations, please look at StoreMetrics.java , RegistryMetrics.java , ServerMetrics.java, or UIMetrics.java respectively.

At the time of writing (0.4.3), the metrics exposed by the namespaces group factcast.server are:

At the time of writing (0.4.3), the metrics exposed by the namespaces group factcast.store are:

At the time of writing (0.4.3), the metrics exposed by the namespaces group factcast.registry are:

gRPC Metrics

If you’re looking for remote calls and their execution times (including marshalling/de-marshalling from protobuf), you can have a look at the metrics automatically added by the gRPC library that we use. The relevant namespaces are:

• grpcServerRequestsReceived and
• grpcServerResponsesSent

These automatically added metrics only focus on service methods defined in the protocol buffer specs. Since a gRPC remote call triggers not everything we want to measure, we introduced additional metrics. When comparing, for instance, the automatically added durations of gRPC vs. the ‘factcast.store.duration’, you will find a subtle difference. The reason for this is that instead of including the gRPC overhead, we chose to only measure the actual invocations on the FactStore/TokenStore implementation. Depending on your needs, you may want to focus on one or the other.

Executor Metrics

Micrometer provides an integration to monitor the default thread pool executor created by Spring Boot. Under the same namespace executor.*, we publish metrics for our own thread pool executors used inside FactCast.

You can distinguish them by the name tag. Currently, these are:

• subscription-factory - used for incoming new subscriptions
• fetching-catchup - used for buffered transformation while using the fetching catchup strategy
• paged-catchup - used for buffered transformation while using the paged catchup strategy
• transformation-cache - used for inserting/updating entries in the transformation cache (only if you use persisted cache)

See https://micrometer.io/docs/ref/jvm for more information.

UI Metrics

Special metrics for the FactCast-Server UI are published via factcast.ui.timer namespace.

Additionally, all methods of the org.factcast.server.ui.adapter.FactRepositoryImpl are measured time-wise, and can be visualized via class and method dimension.