Class: Datadog::Tracing::Sampling::PrioritySampler

Inherits:
Object
  • Object
show all
Defined in:
lib/datadog/tracing/sampling/priority_sampler.rb

Overview

PrioritySampler

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(opts = {}) ⇒ PrioritySampler

Returns a new instance of PrioritySampler.



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# File 'lib/datadog/tracing/sampling/priority_sampler.rb', line 21

def initialize(opts = {})
  @pre_sampler = opts[:base_sampler] || AllSampler.new
  @priority_sampler = opts[:post_sampler] || RateByServiceSampler.new(decision: Sampling::Ext::Decision::AGENT_RATE)
end

Instance Attribute Details

#pre_sampler ⇒ Object (readonly)

NOTE: We do not advise using a pre-sampler. It can save resources, but pre-sampling at rates < 100% may result in partial traces, unless the pre-sampler knows exactly how to drop a span without dropping its ancestors.

Additionally, as service metrics are calculated in the Datadog Agent, the service’s throughput will be underestimated.



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# File 'lib/datadog/tracing/sampling/priority_sampler.rb', line 19

def pre_sampler
  @pre_sampler
end

#priority_sampler ⇒ Object (readonly)

NOTE: We do not advise using a pre-sampler. It can save resources, but pre-sampling at rates < 100% may result in partial traces, unless the pre-sampler knows exactly how to drop a span without dropping its ancestors.

Additionally, as service metrics are calculated in the Datadog Agent, the service’s throughput will be underestimated.



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# File 'lib/datadog/tracing/sampling/priority_sampler.rb', line 19

def priority_sampler
  @priority_sampler
end

Class Method Details

.sampled?(priority_sampling) ⇒ Boolean

Check if the Priority Sampling decision is to keep or drop the trace. Other factors can influence the sampling decision; this method is only responsible for interpreting the Sampling Priority decision.

Parameters:

  • priority_sampling (Integer) —

    priority sampling number

Returns:

  • (Boolean) —

    true if trace is “kept” by priority sampling

  • (Boolean) —

    false if trace is “dropped” by priority sampling



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# File 'lib/datadog/tracing/sampling/priority_sampler.rb', line 90

def self.sampled?(priority_sampling)
  priority_sampling >= Ext::Priority::AUTO_KEEP
end

Instance Method Details

#sample!(trace) ⇒ Object

DEV-2.0:We should get rid of this complicated interaction between @pre_sampler and @priority_sampler. DEV-2.0:If the user wants to configure a custom sampler, we should only allow them to provide a complete DEV-2.0:sampling suite, not having this convoluted support for mixing arbitrary provided samplers in DEV-2.0:the PrioritySampler. Ideally, the PrioritySampler is only used by Datadog. DEV-2.0:There are too many edge cases and combinations to work around currently in this class.



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# File 'lib/datadog/tracing/sampling/priority_sampler.rb', line 31

def sample!(trace)
  # The priority that was set before the sampler ran.
  # This comes from distributed tracing priority propagation.
  distributed_sampling_priority = priority_assigned?(trace)

  # If pre-sampling is configured, do it first. (By default, this will sample at 100%.)
  # NOTE: Pre-sampling at rates < 100% may result in partial traces; not recommended.
  trace.sampled = pre_sample?(trace) ? preserving_priority_sampling(trace) { @pre_sampler.sample!(trace) } : true

  if trace.sampled?
    # If priority sampling has already been applied upstream, use that value.
    return true if priority_assigned?(trace)

    # Check with post sampler how we set the priority.
    sample = priority_sample!(trace)

    # Check if post sampler has already assigned a priority.
    return true if priority_assigned?(trace)

    # If not, use agent priority values.
    priority = sample ? Sampling::Ext::Priority::AUTO_KEEP : Sampling::Ext::Priority::AUTO_REJECT
    assign_priority!(trace, priority)
  else
    # If discarded by pre-sampling, set "reject" priority, so other
    # services for the same trace don't sample needlessly.
    assign_priority!(trace, Sampling::Ext::Priority::AUTO_REJECT)
  end

  trace.sampled?
ensure
  if trace.sampling_priority && trace.sampling_priority > 0
    # Don't modify decision if priority was set upstream.
    if !distributed_sampling_priority && !trace.has_tag?(Tracing::Metadata::Ext::Distributed::TAG_DECISION_MAKER)
      # If no sampling priority being assigned at this point, a custom
      # sampler implementation is configured: this means the user has
      # full control over the sampling decision.
      trace.set_tag(
        Tracing::Metadata::Ext::Distributed::TAG_DECISION_MAKER,
        Sampling::Ext::Decision::MANUAL
      )
    end
  else
    # The sampler decided to not keep this span, removing sampling decision.
    trace.clear_tag(Tracing::Metadata::Ext::Distributed::TAG_DECISION_MAKER)
  end
end

#update(rate_by_service, decision: nil) ⇒ Object 



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# File 'lib/datadog/tracing/sampling/priority_sampler.rb', line 79

def update(rate_by_service, decision: nil)
  @priority_sampler.update(rate_by_service, decision: decision)
end