module Gitlab module Metrics # Class for storing details of a single metric (label, value, etc). class Metric JITTER_RANGE = 0.000001..0.001 attr_reader :series, :values, :tags # series - The name of the series (as a String) to store the metric in. # values - A Hash containing the values to store. # tags - A Hash containing extra tags to add to the metrics. def initialize(series, values, tags = {}) @values = values @series = series @tags = tags end # Returns a Hash in a format that can be directly written to InfluxDB. def to_hash # InfluxDB overwrites an existing point if a new point has the same # series, tag set, and timestamp. In a highly concurrent environment # this means that using the number of seconds since the Unix epoch is # inevitably going to collide with another timestamp. For example, two # Rails requests processed by different processes may end up generating # metrics using the _exact_ same timestamp (in seconds). # # Due to the way InfluxDB is set up there's no solution to this problem, # all we can do is lower the amount of collisions. We do this by using # System.real_time which returns the nanoseconds as a Float providing # greater accuracy. We then add a small random value that is large # enough to distinguish most timestamps but small enough to not alter # the timestamp significantly. # # See https://gitlab.com/gitlab-com/operations/issues/175 for more # information. time = System.real_time(:nanosecond) + rand(JITTER_RANGE) { series: @series, tags: @tags, values: @values, timestamp: time.to_i } end end end end