gitlab-org--gitlab-foss/doc/development/instrumentation.md

Instrumenting Ruby Code

GitLab Performance Monitoring allows instrumenting of custom blocks of Ruby code. This can be used to measure the time spent in a specific part of a larger chunk of code. The resulting data is written to a separate series.

To start measuring a block of Ruby code you should use Gitlab::Metrics.measure and give it a name for the series to store the data in:

Gitlab::Metrics.measure(:user_logins) do
  ...
end

The first argument of this method is the series name and should be plural. This name will be prefixed with rails_ or sidekiq_ depending on whether the code was run in the Rails application or one of the Sidekiq workers. In the above example the final series names would be as follows:

• rails_user_logins
• sidekiq_user_logins

Series names should be plural as this keeps the naming style in line with the other series names.

By default metrics measured using a block contain a single value, "duration", which contains the number of milliseconds it took to execute the block. Custom values can be added by passing a Hash as the 2nd argument. Custom tags can be added by passing a Hash as the 3rd argument. A simple example is as follows:

Gitlab::Metrics.measure(:example_series, { number: 10 }, { class: self.class.to_s }) do
  ...
end