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.

Parameters:

  • trace_flush (Datadog::Tracing::TraceFlush) (defaults to: Flush::Finished.new) —

    responsible for flushing spans from the execution context

  • context_provider (Datadog::Tracing::DefaultContextProvider) (defaults to: DefaultContextProvider.new) —

    ensures different execution contexts have distinct traces

  • default_service (String) (defaults to: Core::Environment::Ext::FALLBACK_SERVICE_NAME) —

    A fallback value for Span#service, as spans without service are rejected

  • enabled (Boolean) (defaults to: true) —

    set if the tracer submits or not spans to the local agent

  • sampler (Datadog::Tracing::Sampler) (defaults to: Sampling::PrioritySampler.new( base_sampler: Sampling::AllSampler.new, post_sampler: Sampling::RuleSampler.new )) —

    a tracer sampler, responsible for filtering out spans when needed

  • tags (Hash) (defaults to: {}) —

    default tags added to all spans

  • writer (Datadog::Tracing::Writer) —

    consumes traces returned by the provided trace_flush



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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.

Parameters:

  • key (Thread) (defaults to: nil) —

    Thread to retrieve trace from. Defaults to current thread. For internal use only.

Returns:



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# File 'lib/datadog/tracing/tracer.rb', line 235

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.

Parameters:

  • key (Thread) (defaults to: nil) —

    Thread to retrieve trace from. Defaults to current thread. For internal use only.

Returns:



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# File 'lib/datadog/tracing/tracer.rb', line 224

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

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

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

The active trace is fiber-local.

Parameters:

  • key (Thread) (defaults to: nil) —

    Thread to retrieve trace from. Defaults to current thread. For internal use only.

Returns:



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# File 'lib/datadog/tracing/tracer.rb', line 213

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

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

Setup a new trace execution context to continue from where another trace left off. This is useful to continue distributed or async traces.

The first span created in the restored context is a direct child of the active span from when the Datadog::Tracing::TraceDigest was created.

When no block is given, the trace context is restored in the current thread. It remains active until the first span created in this restored context is finished. After that, if a new span is created, it start a new, unrelated trace.

When a block is given, the trace context is restored inside the block execution. It remains active until the block ends, even when the first span created inside the block finishes. This means that multiple spans can be direct children of the active span from when the Datadog::Tracing::TraceDigest was created.

Parameters:

Yields:

Returns:



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# File 'lib/datadog/tracing/tracer.rb', line 265

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)
  # When we want the trace to be bound to a block, we cannot let
  # it auto finish when the local root span finishes. This would
  # create mutiple traces inside the block. Instead, we'll
  # expliclity finish the trace after the block finishes.
  auto_finish = !block

  trace = start_trace(continue_from: digest, auto_finish: auto_finish)

  # 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

  if block
    # When a block is given, the trace will be active until the block finishes.
    context.activate!(trace) do
      yield
    ensure # We have to flush even when an error occurs
      # On block completion, force the trace to finish and flush its finished spans.
      # Unfinished spans are lost as the {TraceOperation} has ended.
      trace.finish!
      flush_trace(trace)
    end
  else
    # Otherwise, the trace will be bound to the current thread after this point
    context.activate!(trace)
  end
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 302

def sample_trace(trace_op)
  @sampler.sample!(trace_op) if trace_op.sampling_priority.nil?
rescue => 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

#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 201

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 341

def shutdown!
  return unless @enabled

  @writer&.stop
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() “‘

Parameters:

  • name (String) —

    Span operation name. See / Primary Operations in Services.

  • continue_from (Datadog::Tracing::TraceDigest) (defaults to: nil) —

    continue a trace from a Datadog::Tracing::TraceDigest. Used for linking traces that are executed asynchronously.

  • on_error (Proc) (defaults to: nil) —

    a block that overrides error handling behavior for this operation.

  • resource (String) (defaults to: nil) —

    the resource this span refers, or name if it’s missing

  • service (String) (defaults to: nil) —

    the service name for this span.

  • start_time (Time) (defaults to: nil) —

    time which the span should have started.

  • tags (Hash<String,String>) (defaults to: nil) —

    extra tags which should be added to the span.

  • type (String) (defaults to: nil) —

    the type of the span. See Metadata::Ext::AppTypes.

  • the (Integer) —

    id of the new span.

Yields:

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

Yield Parameters:

Returns:



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# File 'lib/datadog/tracing/tracer.rb', line 132

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 => 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