Class: Datadog::Tracing::Tracer

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

Overview

A Tracer keeps track of the time spent by an application processing a single operation. For example, a trace can be used to track the entire time spent processing a complicated web request. Even though the request may require multiple resources and machines to handle the request, all of these function calls and sub-requests would be encapsulated within a single trace.

Defined Under Namespace

Classes: TraceCompleted

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(trace_flush: Flush::Finished.new, context_provider: DefaultContextProvider.new, default_service: Core::Environment::Ext::FALLBACK_SERVICE_NAME, enabled: true, logger: Datadog.logger, sampler: Sampling::PrioritySampler.new( base_sampler: Sampling::AllSampler.new, post_sampler: Sampling::RuleSampler.new ), span_sampler: Sampling::Span::Sampler.new, tags: {}, writer:) ⇒ Tracer

Initialize a new Datadog::Tracing::Tracer used to create, sample and submit spans that measure the time of sections of code.



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# File 'lib/datadog/tracing/tracer.rb', line 51

def initialize(
  # rubocop:disable Style/KeywordParametersOrder
  # https://github.com/rubocop/rubocop/issues/13933
  trace_flush: Flush::Finished.new,
  context_provider: DefaultContextProvider.new,
  default_service: Core::Environment::Ext::FALLBACK_SERVICE_NAME,
  enabled: true,
  logger: Datadog.logger,
  sampler: Sampling::PrioritySampler.new(
    base_sampler: Sampling::AllSampler.new,
    post_sampler: Sampling::RuleSampler.new
  ),
  span_sampler: Sampling::Span::Sampler.new,
  tags: {},
  # writer is not defaulted because creating it requires agent_settings,
  # which we do not have here and otherwise do not need.
  writer:
  # rubocop:enable Style/KeywordParametersOrder
)
  @trace_flush = trace_flush
  @default_service = default_service
  @enabled = enabled
  @logger = logger
  @provider = context_provider
  @sampler = sampler
  @span_sampler = span_sampler
  @tags = tags
  @writer = writer
end

Instance Attribute Details

#default_service ⇒ Object

Returns the value of attribute default_service.



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# File 'lib/datadog/tracing/tracer.rb', line 34

def default_service
  @default_service
end

#enabled ⇒ Object

Returns the value of attribute enabled.



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# File 'lib/datadog/tracing/tracer.rb', line 34

def enabled
  @enabled
end

#logger ⇒ Object (readonly)

Returns the value of attribute logger.



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# File 'lib/datadog/tracing/tracer.rb', line 26

def logger
  @logger
end

#provider ⇒ Object (readonly)

Returns the value of attribute provider.



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# File 'lib/datadog/tracing/tracer.rb', line 26

def provider
  @provider
end

#sampler ⇒ Object (readonly)

Returns the value of attribute sampler.



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# File 'lib/datadog/tracing/tracer.rb', line 26

def sampler
  @sampler
end

#span_sampler ⇒ Object (readonly)

Returns the value of attribute span_sampler.



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# File 'lib/datadog/tracing/tracer.rb', line 26

def span_sampler
  @span_sampler
end

#tags ⇒ Object (readonly)

Returns the value of attribute tags.



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# File 'lib/datadog/tracing/tracer.rb', line 26

def tags
  @tags
end

#trace_flush ⇒ Object (readonly)

Returns the value of attribute trace_flush.



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# File 'lib/datadog/tracing/tracer.rb', line 26

def trace_flush
  @trace_flush
end

#writer ⇒ Object

Returns the value of attribute writer.



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# File 'lib/datadog/tracing/tracer.rb', line 34

def writer
  @writer
end

Instance Method Details

#active_correlation(key = nil) ⇒ Datadog::Tracing::Correlation::Identifier

Information about the currently active trace.

The most common use cases are tagging log messages and metrics.



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# File 'lib/datadog/tracing/tracer.rb', line 237

def active_correlation(key = nil)
  trace = active_trace(key)

  return Datadog::Tracing::Correlation::Identifier.new unless trace

  trace.to_correlation
end

#active_span(key = nil) ⇒ Datadog::Tracing::SpanOperation?

The active, unfinished span, representing the currently instrumented application section.

The active span belongs to an Datadog::Tracing.active_trace.



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# File 'lib/datadog/tracing/tracer.rb', line 226

def active_span(key = nil)
  trace = active_trace(key)
  trace.active_span if trace
end

#active_trace(key = nil) ⇒ Datadog::Tracing::TraceSegment?

The active, unfinished trace, representing the current instrumentation context.

The active trace is fiber-local.



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# File 'lib/datadog/tracing/tracer.rb', line 215

def active_trace(key = nil)
  call_context(key).active_trace
end

#continue_trace!(digest, key = nil) { ... } ⇒ Object, Datadog::Tracing::TraceOperation

Setup a new trace to continue from where another trace left off.

Used to continue distributed or async traces.

Yields:



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# File 'lib/datadog/tracing/tracer.rb', line 256

def continue_trace!(digest, key = nil, &block)
  # Only accept {TraceDigest} as a digest.
  # Otherwise, create a new execution context.
  digest = nil unless digest.is_a?(TraceDigest)

  # Start a new trace from the digest
  context = call_context(key)
  original_trace = active_trace(key)
  trace = start_trace(continue_from: digest)

  # If block hasn't been given; we need to manually deactivate
  # this trace. Subscribe to the trace finished event to do this.
  subscribe_trace_deactivation!(context, trace, original_trace) unless block

  context.activate!(trace, &block)
end

#sample_trace(trace_op) ⇒ Object

Sample a span, tagging the trace as appropriate.



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# File 'lib/datadog/tracing/tracer.rb', line 274

def sample_trace(trace_op)
  begin
    @sampler.sample!(trace_op)
  rescue StandardError => e
    SAMPLE_TRACE_LOG_ONLY_ONCE.run do
      logger.warn { "Failed to sample trace: #{e.class.name} #{e} at #{Array(e.backtrace).first}" }
    end
  end
end

#set_tags(tags) ⇒ Object

Set the given key / value tag pair at the tracer level. These tags will be appended to each span created by the tracer. Keys and values must be strings.

Examples:

tracer.set_tags('env' => 'prod', 'component' => 'core')



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# File 'lib/datadog/tracing/tracer.rb', line 203

def set_tags(tags)
  string_tags = tags.collect { |k, v| [k.to_s, v] }.to_h
  @tags = @tags.merge(string_tags)
end

#shutdown! ⇒ Object

Shorthand that calls the shutdown! method of a registered worker. It's useful to ensure that the Trace Buffer is properly flushed before shutting down the application.

Examples:

tracer.trace('operation_name', service='rake_tasks') do |span_op|
  span_op.set_tag('task.name', 'script')
end

tracer.shutdown!



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# File 'lib/datadog/tracing/tracer.rb', line 315

def shutdown!
  return unless @enabled

  @writer.stop if @writer
end

#trace(name, continue_from: nil, on_error: nil, resource: nil, service: nil, start_time: nil, tags: nil, type: nil, id: nil) {|span_op, trace_op| ... } ⇒ Object, Datadog::Tracing::SpanOperation

Return a span_op and trace_op that will trace an operation called name.

You could trace your code using a do-block like:

tracer.trace('web.request') do |span_op, trace_op|
  span_op.service = 'my-web-site'
  span_op.resource = '/'
  span_op.set_tag('http.method', request.request_method)
  do_something()
end

The #trace method can also be used without a block in this way:

span_op = tracer.trace('web.request', service: 'my-web-site')
do_something()
span_op.finish()

Remember that in this case, calling SpanOperation#finish is mandatory.

When a Trace is started, #trace will store the created span; subsequent spans will become its children and will inherit some properties:

parent = tracer.trace('parent')   # has no parent span
child  = tracer.trace('child')    # is a child of 'parent'
child.finish()
parent.finish()
parent2 = tracer.trace('parent2') # has no parent span
parent2.finish()

rubocop:disable Metrics/MethodLength

Yields:

  • Optional block where new newly created SpanOperation captures the execution.

Yield Parameters:



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# File 'lib/datadog/tracing/tracer.rb', line 133

def trace(
  name,
  continue_from: nil,
  on_error: nil,
  resource: nil,
  service: nil,
  start_time: nil,
  tags: nil,
  type: nil,
  id: nil,
  &block
)
  return skip_trace(name, &block) unless enabled

  # Resolve the trace
  begin
    context = call_context
    active_trace = context.active_trace
    trace = if continue_from || active_trace.nil?
              start_trace(continue_from: continue_from)
            else
              active_trace
            end
  rescue StandardError => e
    logger.debug { "Failed to trace: #{e}" }

    # Tracing failed: fallback and run code without tracing.
    return skip_trace(name, &block)
  end

  # Activate and start the trace
  if block
    context.activate!(trace) do
      start_span(
        name,
        on_error: on_error,
        resource: resource,
        service: service,
        start_time: start_time,
        tags: tags,
        type: type,
        _trace: trace,
        id: id,
        &block
      )
    end
  else
    # Setup trace activation/deactivation
    manual_trace_activation!(context, trace)

    # Return the new span
    start_span(
      name,
      on_error: on_error,
      resource: resource,
      service: service,
      start_time: start_time,
      tags: tags,
      type: type,
      _trace: trace,
      id: id
    )
  end
end