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Contents
# encoding: utf-8
# This file is distributed under New Relic's license terms.
# See https://github.com/newrelic/rpm/blob/master/LICENSE for complete details.
# This class acts like an Array with a fixed capacity that randomly samples
# from a stream of items such that the probability of each item being included
# in the Array is equal. It uses reservoir sampling in order to achieve this:
# http://xlinux.nist.gov/dads/HTML/reservoirSampling.html
require 'new_relic/agent/event_buffer'
module NewRelic
module Agent
class SampledBuffer < EventBuffer
attr_reader :seen_lifetime, :captured_lifetime
def initialize(capacity)
super
@captured_lifetime = 0
@seen_lifetime = 0
end
def append(x = nil, &blk)
@seen += 1
@seen_lifetime += 1
append_event(x, &blk)
end
def append_event(x = nil, &blk)
raise ArgumentError, "Expected argument or block, but received both" if x && blk
if @items.size < @capacity
x = blk.call if block_given?
@items << x
@captured_lifetime += 1
return x
else
m = rand(@seen) # [0, @seen)
if m < @capacity
x = blk.call if block_given?
@items[m] = x
return x
else
# discard current sample
return nil
end
end
end
def decrement_lifetime_counts_by n
@captured_lifetime -= n
@seen_lifetime -= n
end
def sample_rate_lifetime
@captured_lifetime > 0 ? (@captured_lifetime.to_f / @seen_lifetime) : 0.0
end
def metadata
super.merge!(
:captured_lifetime => @captured_lifetime,
:seen_lifetime => @seen_lifetime
)
end
end
end
end
Version data entries
27 entries across 27 versions & 2 rubygems