Add add operation

Add the add operation to metrics instrumentation classes

The add operation is adding up an array of values

Current implementation

#lib/gitlab/utils/usage_data.rb

def add(*args)
  return -1 if args.any?(&:negative?)

  args.sum
rescue StandardError
   FALLBACK
end

=> add(12, 2, 1)
=> 15

• This operation might not fit under the DatabaseMetric as it is not taking a relation as a parameter.
• This could be a different type of instrumentation class that can handle an array of numbers on which we can have arithmetic operations.
• The same result could be achieved if we use individual GenericMetric instrumentation classes and we might not add a dedicated Metric instrumentation class.

Proposal for API for this metric and operation

BoardsCountMetric < NumbersMetric

operation :add

data { [1, 10] }

The same result could be achieved if we use individual generic metrics for the metric that use add operation. BaseMetric class includes the Gitlab::Utils::UsageData and all the methods are available.

For example:

module Gitlab
  module Usage
    module Metrics
      module Instrumentations
        class CountProjectImports < GnericMetric

        value do
          project_imports = distinct_count(::Project.where(time_period).where.not(import_type: nil), :creator_id)
          bulk_imports = distinct_count(::BulkImport.where(time_period), :user_id)
          jira_issue_imports = distinct_count(::JiraImportState.where(time_period), :user_id)
          csv_issue_imports = distinct_count(Issues::CsvImport.where(time_period), :user_id)
          group_imports = distinct_count(::GroupImportState.where(time_period), :user_id)

          add(project_imports, bulk_imports, jira_issue_imports, csv_issue_imports, group_imports)
        end