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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, :created_at
# 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
@created_at = Time.now.utc
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
# Time#to_f which returns the seconds 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 amount
# of seconds.
#
# See https://gitlab.com/gitlab-com/operations/issues/175 for more
# information.
time = @created_at.to_f + rand(JITTER_RANGE)
{
series: @series,
tags: @tags,
values: @values,
timestamp: (time * 1_000_000_000).to_i
}
end
end
end
end
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