This library contains interfaces that allow clients to log events that are associated with metrics. These events are collected and later analyzed.
Metrics are organized under a Project, which are associated with a Customer. Each of these objects has an integer ID and those IDs are used as parameters in the methods in this file. Metrics can also have one or more dimensions associated with them, which are then passed as a vector of event codes when logging the event.
The default implementation of this service in Fuchsia is Cobalt, which is an end-to-end solution to log, collect and analyze metrics. The two main pillars of Cobalt are protecting user privacy and providing high-quality, aggregate metrics to serve system and component software developers' needs.
To use Cobalt, you must have a Project and one or more Metrics registered with the Cobalt registration system. You must also register one or more Reports in order to see the results of your logging aggregated over all Fuchsia devices. Registration of Projects, Metrics and Reports consists of entries in the YAML files in this repository. In a Fuchsia checkout, this is mapped to //third_party/cobalt_config.
First you use MetricEventLoggerFactory to get a MetricEventLogger for your project. Then you log Events as they occur, using the Log*() methods on it. In the Cobalt FIDL service implementation, Events are accumulated and periodically Observations, derived from the logged Events, are sent to the Cobalt server, where they are used to generate Reports.
MetricEventLoggerFactory: a factory that is used to create a MetricEventLogger for a specific project. Takes a specification identifying a project to log events for. For Cobalt, the specification‘s IDs are specified in Cobalt’s registry repository.
MetricEventLogger: a logger for events that are associated with one project‘s metrics. For Cobalt, the metric_id must be one of the metrics declared in Cobalt’s registry for the project associated with this logger. And each event code in event_codes is a key from the event_codes map of the corresponding MetricDimension for the metric in Cobalt's registry.
In addition, for Cobalt, the following applies to each of the MetricEventLogger methods:
LogOccurrence: metric_id must correspond to a metric of type OCCURRENCE.
LogInteger: metric_id must correspond to a metric of type INTEGER.
LogIntegerHistogram: metric_id must correspond to a metric of type INTEGER_HISTOGRAM.
LogString: metric_id must correspond to a metric of type STRING.
LogCustomEvent: metric_id must correspond to a metric of type CUSTOM, and the event_values must have a dimension name and type of value that matches the field names and their types for the metric as declared in Cobalt's registry.