Add sample_rand to transaction

Author: solnic

sentry-ruby/lib/sentry/transaction.rb

@@ -2,6 +2,7 @@
 
 require "sentry/baggage"
 require "sentry/profiler"
+require "sentry/utils/sample_rand"
 require "sentry/propagation_context"
 
 module Sentry
@@ -57,12 +58,17 @@ class Transaction < Span
     # @return [Profiler]
     attr_reader :profiler
 
+    # Sample rand value generated from trace_id
+    # @return [String]
+    attr_reader :sample_rand
+
     def initialize(
       hub:,
       name: nil,
       source: :custom,
       parent_sampled: nil,
       baggage: nil,
+      sample_rand: nil,
       **options
     )
       super(transaction: self, **options)
@@ -82,12 +88,15 @@ def initialize(
       @effective_sample_rate = nil
       @contexts = {}
       @measurements = {}
+      @sample_rand = sample_rand
 
       unless @hub.profiler_running?
         @profiler = @configuration.profiler_class.new(@configuration)
       end
 
       init_span_recorder
+
+      @sample_rand ||= Utils::SampleRand.generate_from_trace_id(@trace_id)
     end
 
     # @deprecated use Sentry.continue_trace instead.
@@ -123,12 +132,15 @@ def self.from_sentry_trace(sentry_trace, baggage: nil, hub: Sentry.get_current_h
 
       baggage.freeze!
 
+      sample_rand = extract_sample_rand_from_baggage(baggage, trace_id, parent_sampled)
+
       new(
         trace_id: trace_id,
         parent_span_id: parent_span_id,
         parent_sampled: parent_sampled,
         hub: hub,
         baggage: baggage,
+        sample_rand: sample_rand,
         **options
       )
     end
@@ -139,6 +151,24 @@ def self.extract_sentry_trace(sentry_trace)
       PropagationContext.extract_sentry_trace(sentry_trace)
     end
 
+    def self.extract_sample_rand_from_baggage(baggage, trace_id, parent_sampled)
+      return Utils::SampleRand.generate_from_trace_id(trace_id) unless baggage&.items
+
+      sample_rand_str = baggage.items["sample_rand"]
+      if sample_rand_str && Utils::SampleRand.valid?(sample_rand_str.to_f)
+        sample_rand_str.to_f
+      else
+        sample_rate_str = baggage.items["sample_rate"]
+        sample_rate = sample_rate_str&.to_f
+
+        if sample_rate && parent_sampled != nil
+          Utils::SampleRand.generate_from_sampling_decision(parent_sampled, sample_rate, trace_id)
+        else
+          Utils::SampleRand.generate_from_trace_id(trace_id)
+        end
+      end
+    end
+
     # @return [Hash]
     def to_hash
       hash = super
@@ -153,6 +183,13 @@ def to_hash
       hash
     end
 
+    def parent_sample_rate
+      return unless @baggage&.items
+
+      sample_rate_str = @baggage.items["sample_rate"]
+      sample_rate_str&.to_f
+    end
+
     # @return [Transaction]
     def deep_dup
       copy = super
@@ -225,7 +262,7 @@ def set_initial_sample_decision(sampling_context:)
           @effective_sample_rate /= 2**factor
         end
 
-        @sampled = Random.rand < @effective_sample_rate
+        @sampled = @sample_rand < @effective_sample_rate
       end
 
       if @sampled
@@ -331,6 +368,7 @@ def populate_head_baggage
       items = {
         "trace_id" => trace_id,
         "sample_rate" => effective_sample_rate&.to_s,
+        "sample_rand" => Utils::SampleRand.format(@sample_rand),
         "sampled" => sampled&.to_s,
         "environment" => @environment,
         "release" => @release,

sentry-ruby/spec/sentry/client_spec.rb

@@ -273,6 +273,7 @@ def sentry_context
       expect(event.dynamic_sampling_context).to eq({
         "environment" => "development",
         "public_key" => "12345",
+        "sample_rand" => Sentry::Utils::SampleRand.format(transaction.sample_rand),
         "sample_rate" => "1.0",
         "sampled" => "true",
         "transaction" => "test transaction",

sentry-ruby/spec/sentry/net/http_spec.rb

@@ -153,6 +153,7 @@
       expect(request["baggage"]).to eq(
         "sentry-trace_id=#{transaction.trace_id},"\
         "sentry-sample_rate=1.0,"\
+        "sentry-sample_rand=#{Sentry::Utils::SampleRand.format(transaction.sample_rand)},"\
         "sentry-sampled=true,"\
         "sentry-environment=development,"\
         "sentry-public_key=foobarbaz"

sentry-ruby/spec/sentry/rack/capture_exceptions_spec.rb

@@ -279,11 +279,11 @@ def verify_transaction_doesnt_inherit_external_transaction(transaction, external
       end
 
       def wont_be_sampled_by_sdk
-        allow(Random).to receive(:rand).and_return(1.0)
+        allow(Sentry::Utils::SampleRand).to receive(:generate_from_trace_id).and_return(1.0)
       end
 
       def will_be_sampled_by_sdk
-        allow(Random).to receive(:rand).and_return(0.3)
+        allow(Sentry::Utils::SampleRand).to receive(:generate_from_trace_id).and_return(0.3)
       end
 
       before do
@@ -430,7 +430,7 @@ def will_be_sampled_by_sdk
 
     context "when the transaction is sampled" do
       before do
-        allow(Random).to receive(:rand).and_return(0.4)
+        allow(Sentry::Utils::SampleRand).to receive(:generate_from_trace_id).and_return(0.4)
       end
 
       it "starts a transaction and finishes it" do
@@ -488,7 +488,7 @@ def will_be_sampled_by_sdk
 
     context "when the transaction is not sampled" do
       before do
-        allow(Random).to receive(:rand).and_return(0.6)
+        allow(Sentry::Utils::SampleRand).to receive(:generate_from_trace_id).and_return(1.0)
       end
 
       it "doesn't do anything" do
@@ -506,7 +506,7 @@ def will_be_sampled_by_sdk
 
     context "when there's an exception" do
       before do
-        allow(Random).to receive(:rand).and_return(0.4)
+        allow(Sentry::Utils::SampleRand).to receive(:generate_from_trace_id).and_return(0.4)
       end
 
       it "still finishes the transaction" do

sentry-ruby/spec/sentry/transaction_spec.rb

@@ -257,22 +257,24 @@
         end
 
         it "uses traces_sample_rate for sampling (positive result)" do
-          allow(Random).to receive(:rand).and_return(0.4)
+          # Create transaction with sample_rand < sample_rate (0.5) to ensure sampled
+          transaction = described_class.new(op: "rack.request", hub: Sentry.get_current_hub, sample_rand: 0.4)
 
-          subject.set_initial_sample_decision(sampling_context: {})
-          expect(subject.sampled).to eq(true)
-          expect(subject.effective_sample_rate).to eq(0.5)
+          transaction.set_initial_sample_decision(sampling_context: {})
+          expect(transaction.sampled).to eq(true)
+          expect(transaction.effective_sample_rate).to eq(0.5)
           expect(string_io.string).to include(
             "[Tracing] Starting <rack.request> transaction"
           )
         end
 
         it "uses traces_sample_rate for sampling (negative result)" do
-          allow(Random).to receive(:rand).and_return(0.6)
+          # Create transaction with sample_rand > sample_rate (0.5) to ensure not sampled
+          transaction = described_class.new(op: "rack.request", hub: Sentry.get_current_hub, sample_rand: 0.6)
 
-          subject.set_initial_sample_decision(sampling_context: {})
-          expect(subject.sampled).to eq(false)
-          expect(subject.effective_sample_rate).to eq(0.5)
+          transaction.set_initial_sample_decision(sampling_context: {})
+          expect(transaction.sampled).to eq(false)
+          expect(transaction.effective_sample_rate).to eq(0.5)
           expect(string_io.string).to include(
             "[Tracing] Discarding <rack.request> transaction because it's not included in the random sample (sampling rate = 0.5)"
           )
@@ -474,11 +476,21 @@
       end
 
       it "submits the event with the transaction's hub by default" do
-        subject.instance_variable_set(:@hub, another_hub)
+        # Create transaction with the specific hub from the beginning
+        transaction = described_class.new(
+          op: "sql.query",
+          description: "SELECT * FROM users;",
+          status: "ok",
+          sampled: true,
+          parent_sampled: true,
+          name: "foo",
+          source: :view,
+          hub: another_hub
+        )
 
         expect(another_hub).to receive(:capture_event)
 
-        subject.finish
+        transaction.finish
       end
     end
 
@@ -511,9 +523,13 @@
       it "records lost event with reason backpressure" do
         expect(Sentry.get_current_client.transport).to receive(:any_rate_limited?).and_return(true)
         Sentry.backpressure_monitor.run
-        allow(Random).to receive(:rand).and_return(0.6)
 
-        subject.finish
+        # Create transaction with sample_rand that will be rejected after backpressure downsampling
+        # With traces_sample_rate = 1.0 and downsample_factor = 1, effective rate becomes 0.5
+        # So sample_rand = 0.6 > 0.5 will be rejected
+        transaction = described_class.new(hub: Sentry.get_current_hub, sample_rand: 0.6)
+
+        transaction.finish
         expect(Sentry.get_current_client.transport).to have_recorded_lost_event(:backpressure, 'transaction')
         expect(Sentry.get_current_client.transport).to have_recorded_lost_event(:backpressure, 'span')
       end
@@ -556,7 +572,8 @@
         name: "foo",
         source: source,
         hub: Sentry.get_current_hub,
-        baggage: incoming_baggage
+        baggage: incoming_baggage,
+        sample_rand: 0.123456  # Use a known value for predictable testing
       )
 
       transaction.set_initial_sample_decision(sampling_context: {})
@@ -574,6 +591,7 @@
         expect(baggage.items).to eq({
           "environment" => "development",
           "public_key" => "12345",
+          "sample_rand" => "0.123456",  # Known value from transaction creation
           "trace_id" => subject.trace_id,
           "transaction"=>"foo",
           "sample_rate" => "1.0",
@@ -630,6 +648,7 @@
         expect(baggage.items).to eq({
           "environment" => "development",
           "public_key" => "12345",
+          "sample_rand" => "0.123456",  # Known value from transaction creation
           "trace_id" => subject.trace_id,
           "transaction"=>"foo",
           "sample_rate" => "1.0",