chore: deprecate sampling delegation (#192)

Author: dmehala

doc/sampling-delegation.md

@@ -74,12 +74,6 @@ int main() {
       span.set_error_message(httplib::to_string(er));
       std::cerr << "Error occurred while proxying request: " << req.target
                 << "\n";
-    } else {
-      tracingutil::HeaderReader reader(res.headers);
-      auto status = span.read_sampling_delegation_response(reader);
-      if (auto error = status.if_error()) {
-        std::cerr << error << "\n";
-      }
     }
 
     span.set_tag("http.status_code", std::to_string(res.status));

examples/http-server/proxy/proxy.cpp

@@ -159,10 +159,6 @@ int main() {
   // created. We finish it by popping it off of the span stack.
   server.set_post_routing_handler([](const httplib::Request& request, httplib::Response& response) {
     auto* context = static_cast<RequestTracingContext*>(request.user_data.get());
-
-    tracingutil::HeaderWriter writer(response.headers);
-    context->spans.top().trace_segment().write_sampling_delegation_response(writer);
-
     context->spans.pop();
     return httplib::Server::HandlerResponse::Unhandled;
   });

examples/http-server/server/server.cpp

@@ -34,7 +34,6 @@ namespace environment {
   MACRO(DD_SERVICE)                                  \
   MACRO(DD_SPAN_SAMPLING_RULES)                      \
   MACRO(DD_SPAN_SAMPLING_RULES_FILE)                 \
-  MACRO(DD_TRACE_DELEGATE_SAMPLING)                  \
   MACRO(DD_TRACE_PROPAGATION_STYLE_EXTRACT)          \
   MACRO(DD_TRACE_PROPAGATION_STYLE_INJECT)           \
   MACRO(DD_TRACE_PROPAGATION_STYLE)                  \

include/datadog/environment.h

@@ -4,20 +4,10 @@
 // parameters to `Span::inject` that alter the behavior of trace context
 // propagation.
 
-#include "optional.h"
-
 namespace datadog {
 namespace tracing {
 
-struct InjectionOptions {
-  // If this tracer is using the "Datadog" propagation injection style, then
-  // include a request header that indicates that whoever extracts this trace
-  // context "on the other side" may make their own trace sampling decision
-  // and convey it back to us in a response header. If
-  // `delegate_sampling_decision` is null, then its value depends on the tracer
-  // configuration (see `TracerConfig::delegate_trace_sampling`).
-  Optional<bool> delegate_sampling_decision;
-};
+struct InjectionOptions {};
 
 }  // namespace tracing
 }  // namespace datadog

include/datadog/injection_options.h

@@ -66,7 +66,6 @@ class Span {
   std::function<std::uint64_t()> generate_span_id_;
   Clock clock_;
   Optional<std::chrono::steady_clock::time_point> end_time_;
-  mutable bool expecting_delegated_sampling_decision_;
 
  public:
   // Create a span whose properties are stored in the specified `data`, that is
@@ -169,13 +168,6 @@ class Span {
   void inject(DictWriter& writer) const;
   void inject(DictWriter& writer, const InjectionOptions& options) const;
 
-  // If this span is expecting a sampling decision that it previously delegated,
-  // then extract a sampling decision from the specified `reader`. Return an
-  // error if a sampling decision is present in `reader` but is invalid. Return
-  // success otherwise. The trace segment associated with this span might adopt
-  // the sampling decision from `reader`.
-  Expected<void> read_sampling_delegation_response(const DictReader& reader);
-
   // Return a reference to this span's trace segment.  The trace segment has
   // member functions that affect the trace as a whole, such as
   // `TraceSegment::override_sampling_priority`.

include/datadog/span.h

@@ -79,25 +79,6 @@ class TraceSegment {
 
   std::shared_ptr<ConfigManager> config_manager_;
 
-  // See `doc/sampling-delegation.md` for more information about
-  // `struct SamplingDelegation`.
-  struct SamplingDelegation {
-    // This segment is configured to delegate its sampling decision.
-    bool enabled;
-    // The trace context from which the local root span was extracted delegated
-    // the sampling decision to this segment.
-    bool decision_was_delegated_to_me;
-    // This segment included a request for sampling delegation in outbound
-    // injected trace context (see `inject`).
-    bool sent_request_header;
-    // This segment received a (presumably delegated) sampling decision. See
-    // `read_sampling_delegation_response`.
-    bool received_matching_response_header;
-    // This segment conveyed a sampling decision back to a parent service that
-    // had previously requested a delegated sampling decision.
-    bool sent_response_header;
-  } sampling_delegation_ = {};
-
  public:
   TraceSegment(const std::shared_ptr<Logger>& logger,
                const std::shared_ptr<Collector>& collector,
@@ -106,8 +87,7 @@ class TraceSegment {
                const std::shared_ptr<SpanSampler>& span_sampler,
                const std::shared_ptr<const SpanDefaults>& defaults,
                const std::shared_ptr<ConfigManager>& config_manager,
-               const RuntimeID& runtime_id, bool sampling_delegation_enabled,
-               bool sampling_decision_was_delegated_to_me,
+               const RuntimeID& runtime_id,
                const std::vector<PropagationStyle>& injection_styles,
                const Optional<std::string>& hostname,
                Optional<std::string> origin, std::size_t tags_header_max_size,
@@ -131,14 +111,6 @@ class TraceSegment {
   bool inject(DictWriter& writer, const SpanData& span,
               const InjectionOptions& options);
 
-  // Inject this segment's trace sampling decision into the specified `writer`,
-  // if appropriate.
-  void write_sampling_delegation_response(DictWriter& writer);
-
-  // Extract a trace sampling decision from the specified `reader` if it has
-  // one, and use the resulting decision, if appropriate.
-  Expected<void> read_sampling_delegation_response(const DictReader& reader);
-
   // Take ownership of the specified `span`.
   void register_span(std::unique_ptr<SpanData> span);
   // Increment the number of finished spans.  If that number is equal to the

include/datadog/trace_segment.h

@@ -49,7 +49,6 @@ class Tracer {
   std::vector<PropagationStyle> extraction_styles_;
   Optional<std::string> hostname_;
   std::size_t tags_header_max_size_;
-  bool sampling_delegation_enabled_;
   // Store the tracer configuration in an in-memory file, allowing it to be
   // read to determine if the process is instrumented with a tracer and to
   // retrieve relevant tracing information.

include/datadog/tracer.h

@@ -80,11 +80,6 @@ struct TracerConfig {
   // `telemetry/configuration.h` By default, the telemetry module is enabled.
   telemetry::Configuration telemetry;
 
-  // `delegate_trace_sampling` indicates whether the tracer will consult a child
-  // service for a trace sampling decision, and prefer the resulting decision
-  // over its own, if appropriate.
-  Optional<bool> delegate_trace_sampling;
-
   // `trace_sampler` configures trace sampling.  Trace sampling determines which
   // traces are sent to Datadog.  See `trace_sampler_config.h`.
   TraceSamplerConfig trace_sampler;
@@ -199,7 +194,6 @@ class FinalizedTracerConfig final {
   Clock clock;
   std::string integration_name;
   std::string integration_version;
-  bool delegate_trace_sampling;
   bool report_traces;
   std::unordered_map<ConfigName, ConfigMetadata> metadata;
   Baggage::Options baggage_opts;

include/datadog/tracer_config.h

@@ -20,7 +20,6 @@ struct ExtractedData {
   Optional<std::uint64_t> parent_id;
   Optional<std::string> origin;
   std::vector<std::pair<std::string, std::string>> trace_tags;
-  bool delegate_sampling_decision = false;
   Optional<int> sampling_priority;
   // If this `ExtractedData` was created on account of `PropagationStyle::W3C`,
   // then `datadog_w3c_parent_id` contains the parts of the "tracestate"