RUM-15138: Rebase trace sample rate against RUM session sample rate for correlated cross-product sampling

dd-sdk-android-core/api/apiSurface

@@ -381,8 +381,8 @@ open class com.datadog.android.core.sampling.DeterministicSampler<T: Any> : Samp
   override fun getSampleRate(): Float
   companion object 
     const val SAMPLE_ALL_RATE: Float
-    const val SAMPLER_HASHER: ULong
-    const val MAX_ID: ULong
+    DEPRECATED const val SAMPLER_HASHER: ULong
+    DEPRECATED const val MAX_ID: ULong
 open class com.datadog.android.core.sampling.RateBasedSampler<T: Any> : Sampler<T>
   constructor(() -> Float)
   constructor(Float)
@@ -448,6 +448,7 @@ object com.datadog.android.log.LogAttributes
   const val RUM_SESSION_ID: String
   const val RUM_VIEW_ID: String
   const val RUM_ACTION_ID: String
+  const val RUM_SESSION_SAMPLE_RATE: String
   const val SERVICE_NAME: String
   const val SOURCE: String
   const val STATUS: String

dd-sdk-android-core/api/dd-sdk-android-core.api

@@ -1081,6 +1081,7 @@ public final class com/datadog/android/log/LogAttributes {
 	public static final field RUM_ACTION_ID Ljava/lang/String;
 	public static final field RUM_APPLICATION_ID Ljava/lang/String;
 	public static final field RUM_SESSION_ID Ljava/lang/String;
+	public static final field RUM_SESSION_SAMPLE_RATE Ljava/lang/String;
 	public static final field RUM_VIEW_ID Ljava/lang/String;
 	public static final field SERVICE Ljava/lang/String;
 	public static final field SERVICE_NAME Ljava/lang/String;

dd-sdk-android-core/src/main/kotlin/com/datadog/android/core/sampling/DeterministicSampler.kt

@@ -8,6 +8,7 @@ package com.datadog.android.core.sampling
 
 import androidx.annotation.FloatRange
 import com.datadog.android.api.InternalLogger
+import com.datadog.android.internal.sampling.computeSamplingDecision
 
 /**
  * [Sampler] with the given sample rate using a deterministic algorithm for a stable
@@ -46,19 +47,8 @@ open class DeterministicSampler<T : Any>(
     ) : this(idConverter, sampleRate.toFloat())
 
     /** @inheritDoc */
-    override fun sample(item: T): Boolean {
-        val sampleRate = getSampleRate()
-
-        return when {
-            sampleRate >= SAMPLE_ALL_RATE -> true
-            sampleRate <= 0f -> false
-            else -> {
-                val hash = idConverter(item) * SAMPLER_HASHER
-                val threshold = (MAX_ID.toDouble() * sampleRate / SAMPLE_ALL_RATE).toULong()
-                hash < threshold
-            }
-        }
-    }
+    override fun sample(item: T): Boolean =
+        computeSamplingDecision(getSampleRate(), idConverter(item))
 
     /** @inheritDoc */
     override fun getSampleRate(): Float {
@@ -93,11 +83,13 @@ open class DeterministicSampler<T : Any>(
          * within the [DeterministicSampler] implementation. This value is a good number for
          * Knuth hashing (large, prime, fit in 64 bit long).
          */
+        @Deprecated("RUM-13454: Implementation detail, will be removed in v4 (RUM-15590).")
         const val SAMPLER_HASHER: ULong = 1111111111111111111u
 
         /**
          * The maximum value used as an upper limit for computing hash-based sampling thresholds.
          */
+        @Deprecated("RUM-13454: Implementation detail, will be removed in v4 (RUM-15590).")
         const val MAX_ID: ULong = 0xFFFFFFFFFFFFFFFFUL
     }
 }

dd-sdk-android-core/src/main/kotlin/com/datadog/android/log/LogAttributes.kt

@@ -279,6 +279,13 @@ object LogAttributes {
      */
     const val RUM_ACTION_ID: String = "user_action.id"
 
+    /**
+     * Key for the RUM session sample rate used for cross-product trace sampling rebasing.
+     * This key is written to spans by [com.datadog.android.trace.internal.RumContextPropagator]
+     * and read by [com.datadog.android.trace.DeterministicTraceSampler].
+     */
+    const val RUM_SESSION_SAMPLE_RATE: String = "session_sample_rate"
+
     /**
      * The name of the application or service generating the log events. (String)
      * This value is filled automatically by the [Logger].

dd-sdk-android-internal/api/apiSurface

@@ -164,6 +164,7 @@ sealed class com.datadog.android.internal.profiling.ProfilerStopEvent
     constructor(TTIDRumContext? = null)
 data class com.datadog.android.internal.profiling.TTIDRumContext
   constructor(String, String, String, String?, String?, String?)
+fun computeSamplingDecision(Float, ULong): Boolean
 interface com.datadog.android.internal.system.BuildSdkVersionProvider
   val version: Int
   val isAtLeastN: Boolean

dd-sdk-android-internal/api/dd-sdk-android-internal.api

@@ -310,6 +310,10 @@ public final class com/datadog/android/internal/profiling/TTIDRumContext {
 	public fun toString ()Ljava/lang/String;
 }
 
+public final class com/datadog/android/internal/sampling/DeterministicSamplingKt {
+	public static final fun computeSamplingDecision-2TYgG_w (FJ)Z
+}
+
 public abstract interface class com/datadog/android/internal/system/BuildSdkVersionProvider {
 	public static final field Companion Lcom/datadog/android/internal/system/BuildSdkVersionProvider$Companion;
 	public abstract fun getVersion ()I

dd-sdk-android-internal/src/main/java/com/datadog/android/internal/sampling/DeterministicSampling.kt

@@ -0,0 +1,30 @@
+/*
+ * Unless explicitly stated otherwise all files in this repository are licensed under the Apache License Version 2.0.
+ * This product includes software developed at Datadog (https://www.datadoghq.com/).
+ * Copyright 2016-Present Datadog, Inc.
+ */
+
+package com.datadog.android.internal.sampling
+
+private const val SAMPLE_ALL_RATE: Float = 100f
+private const val SAMPLER_HASHER: ULong = 1111111111111111111u
+private const val MAX_ID: ULong = 0xFFFFFFFFFFFFFFFFUL
+
+/**
+ * Computes a deterministic sampling decision based on the given sample rate and identifier.
+ *
+ * @param sampleRate the sample rate in the range [0, 100].
+ * @param id a stable numerical identifier derived from the item being sampled.
+ * @return true if the item should be sampled, false otherwise.
+ */
+fun computeSamplingDecision(sampleRate: Float, id: ULong): Boolean {
+    return when {
+        sampleRate >= SAMPLE_ALL_RATE -> true
+        sampleRate <= 0f -> false
+        else -> {
+            val hash = id * SAMPLER_HASHER
+            val threshold = (MAX_ID.toDouble() * sampleRate / SAMPLE_ALL_RATE).toULong()
+            hash < threshold
+        }
+    }
+}

dd-sdk-android-internal/src/test/java/com/datadog/android/internal/sampling/DeterministicSamplingTest.kt

@@ -0,0 +1,67 @@
+/*
+ * Unless explicitly stated otherwise all files in this repository are licensed under the Apache License Version 2.0.
+ * This product includes software developed at Datadog (https://www.datadoghq.com/).
+ * Copyright 2016-Present Datadog, Inc.
+ */
+
+package com.datadog.android.internal.sampling
+
+import fr.xgouchet.elmyr.annotation.FloatForgery
+import fr.xgouchet.elmyr.annotation.LongForgery
+import fr.xgouchet.elmyr.junit5.ForgeExtension
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.RepeatedTest
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.extension.ExtendWith
+import org.junit.jupiter.api.extension.Extensions
+import org.mockito.junit.jupiter.MockitoExtension
+import org.mockito.junit.jupiter.MockitoSettings
+import org.mockito.quality.Strictness
+
+@Extensions(
+    ExtendWith(MockitoExtension::class),
+    ExtendWith(ForgeExtension::class)
+)
+@MockitoSettings(strictness = Strictness.LENIENT)
+internal class DeterministicSamplingTest {
+
+    @RepeatedTest(32)
+    fun `M always return true W computeSamplingDecision() {sampleRate is 100}`(
+        @LongForgery fakeId: Long
+    ) {
+        assertThat(computeSamplingDecision(100f, fakeId.toULong())).isTrue()
+    }
+
+    @RepeatedTest(32)
+    fun `M always return true W computeSamplingDecision() {sampleRate above 100}`(
+        @FloatForgery(min = 100.01f, max = 200f) fakeSampleRate: Float,
+        @LongForgery fakeId: Long
+    ) {
+        assertThat(computeSamplingDecision(fakeSampleRate, fakeId.toULong())).isTrue()
+    }
+
+    @RepeatedTest(32)
+    fun `M always return false W computeSamplingDecision() {sampleRate is 0}`(
+        @LongForgery fakeId: Long
+    ) {
+        assertThat(computeSamplingDecision(0f, fakeId.toULong())).isFalse()
+    }
+
+    @RepeatedTest(32)
+    fun `M always return false W computeSamplingDecision() {sampleRate below 0}`(
+        @FloatForgery(min = -100f, max = -0.01f) fakeSampleRate: Float,
+        @LongForgery fakeId: Long
+    ) {
+        assertThat(computeSamplingDecision(fakeSampleRate, fakeId.toULong())).isFalse()
+    }
+
+    @Test
+    fun `M return deterministic result W computeSamplingDecision() {same id same rate}`(
+        @FloatForgery(min = 1f, max = 99f) fakeSampleRate: Float,
+        @LongForgery fakeId: Long
+    ) {
+        val first = computeSamplingDecision(fakeSampleRate, fakeId.toULong())
+        val second = computeSamplingDecision(fakeSampleRate, fakeId.toULong())
+        assertThat(first).isEqualTo(second)
+    }
+}

detekt_custom_safe_calls.yml

@@ -1132,6 +1132,7 @@ datadog:
       - "kotlin.Double.toInt()"
       - "kotlin.Double.toLong()"
       - "kotlin.Double.toULong()"
+      - "kotlin.Float.coerceAtMost(kotlin.Float)"
       - "kotlin.Float.fromBits(kotlin.Int)"
       - "kotlin.Float.percent()"
       - "kotlin.Float.roundToInt()"

features/dd-sdk-android-rum/src/main/kotlin/com/datadog/android/rum/internal/domain/RumContext.kt

@@ -25,7 +25,8 @@ internal data class RumContext(
     val syntheticsResultId: String? = null,
     val viewTimestamp: Long = 0L,
     val viewTimestampOffset: Long = 0L,
-    val hasReplay: Boolean = false
+    val hasReplay: Boolean = false,
+    val sessionSampleRate: Float = FULL_SESSION_SAMPLE_RATE
 ) {
 
     fun toMap(): Map<String, Any?> {
@@ -44,7 +45,8 @@ internal data class RumContext(
             SYNTHETICS_RESULT_ID to syntheticsResultId,
             VIEW_TIMESTAMP to viewTimestamp,
             HAS_REPLAY to hasReplay,
-            VIEW_TIMESTAMP_OFFSET to viewTimestampOffset
+            VIEW_TIMESTAMP_OFFSET to viewTimestampOffset,
+            SESSION_SAMPLE_RATE to sessionSampleRate
         )
     }
 
@@ -68,6 +70,8 @@ internal data class RumContext(
         const val HAS_REPLAY = "view_has_replay"
         const val VIEW_TIMESTAMP = "view_timestamp"
         const val VIEW_TIMESTAMP_OFFSET = "view_timestamp_offset"
+        const val SESSION_SAMPLE_RATE = "session_sample_rate"
+        const val FULL_SESSION_SAMPLE_RATE: Float = 100f
 
         fun fromFeatureContext(featureContext: Map<String, Any?>): RumContext {
             val applicationId = featureContext[APPLICATION_ID] as? String
@@ -89,6 +93,8 @@ internal data class RumContext(
             val hasReplay = featureContext[HAS_REPLAY] as? Boolean ?: false
             val viewTimestamp = featureContext[VIEW_TIMESTAMP] as? Long ?: 0L
             val viewTimestampOffset = featureContext[VIEW_TIMESTAMP_OFFSET] as? Long ?: 0L
+            val sessionSampleRate = (featureContext[SESSION_SAMPLE_RATE] as? Number)
+                ?.toFloat() ?: FULL_SESSION_SAMPLE_RATE
 
             return RumContext(
                 applicationId = applicationId ?: NULL_UUID,
@@ -105,7 +111,8 @@ internal data class RumContext(
                 syntheticsResultId = syntheticsResultId,
                 viewTimestamp = viewTimestamp,
                 viewTimestampOffset = viewTimestampOffset,
-                hasReplay = hasReplay
+                hasReplay = hasReplay,
+                sessionSampleRate = sessionSampleRate
             )
         }
     }

features/dd-sdk-android-rum/src/main/kotlin/com/datadog/android/rum/internal/domain/scope/RumSessionScope.kt

@@ -65,6 +65,7 @@ internal class RumSessionScope(
 
     internal var sessionId = RumContext.NULL_UUID
     internal var sessionState: State = State.NOT_TRACKED
+    internal var sessionSampleRate: Float = sessionSampler.getSampleRate() ?: RumContext.FULL_SESSION_SAMPLE_RATE
     private var startReason: StartReason = StartReason.USER_APP_LAUNCH
     internal var isActive: Boolean = true
     private val sessionStartNs = AtomicLong(sdkCore.timeProvider.getDeviceElapsedTimeNanos())
@@ -211,7 +212,8 @@ internal class RumSessionScope(
             sessionId = sessionId,
             sessionState = sessionState,
             sessionStartReason = startReason,
-            isSessionActive = isActive
+            isSessionActive = isActive,
+            sessionSampleRate = sessionSampleRate
         )
     }
 

features/dd-sdk-android-rum/src/test/kotlin/com/datadog/android/rum/internal/domain/RumContextTest.kt

@@ -7,11 +7,13 @@
 package com.datadog.android.rum.internal.domain
 
 import com.datadog.android.rum.utils.forge.Configurator
+import fr.xgouchet.elmyr.Forge
 import fr.xgouchet.elmyr.annotation.Forgery
 import fr.xgouchet.elmyr.junit5.ForgeConfiguration
 import fr.xgouchet.elmyr.junit5.ForgeExtension
 import org.assertj.core.api.Assertions.assertThat
 import org.junit.jupiter.api.RepeatedTest
+import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.extension.ExtendWith
 
 @ExtendWith(ForgeExtension::class)
@@ -28,4 +30,19 @@ internal class RumContextTest {
         // Then
         assertThat(anotherRumContext).isEqualTo(fakeRumContext)
     }
+
+    @Test
+    fun `M parse session sample rate W fromFeatureContext() {value is Double}`(forge: Forge) {
+        // Given: use an explicit Double to verify that as? Number handles Double (as? Float would return null)
+        val fakeDouble: Double = forge.aDouble(min = 0.0, max = 100.0)
+        val featureContext = mapOf<String, Any?>(
+            RumContext.SESSION_SAMPLE_RATE to fakeDouble
+        )
+
+        // When
+        val rumContext = RumContext.fromFeatureContext(featureContext)
+
+        // Then
+        assertThat(rumContext.sessionSampleRate).isEqualTo(fakeDouble.toFloat())
+    }
 }

features/dd-sdk-android-rum/src/test/kotlin/com/datadog/android/rum/internal/domain/scope/RumSessionScopeTest.kt

@@ -266,6 +266,16 @@ internal class RumSessionScopeTest {
         assertThat(childScope?.sampleRate).isCloseTo(fakeSampleRate, offset(0.001f))
     }
 
+    @Test
+    fun `M use full session sample rate W init() { getSampleRate returns null }`() {
+        // Given
+        whenever(mockSessionSampler.getSampleRate()).thenReturn(null)
+        initializeTestedScope(withMockChildScope = false)
+
+        // Then
+        assertThat(testedScope.sessionSampleRate).isEqualTo(RumContext.FULL_SESSION_SAMPLE_RATE)
+    }
+
     @Test
     fun `M delegate events to child scope W handleViewEvent() {TRACKED}`(
         forge: Forge
@@ -478,6 +488,23 @@ internal class RumSessionScopeTest {
         assertThat(context.viewId).isEqualTo(fakeParentContext.viewId)
     }
 
+    @Test
+    fun `M use full session sample rate W getRumContext() {getSampleRate returns null}`(
+        forge: Forge
+    ) {
+        // Given
+        whenever(mockSessionSampler.getSampleRate()).thenReturn(null)
+        whenever(mockSessionSampler.sample(any())).thenReturn(true)
+        initializeTestedScope()
+
+        // When
+        testedScope.handleEvent(forge.startViewEvent(), fakeDatadogContext, mockEventWriteScope, mockWriter)
+        val context = testedScope.getRumContext()
+
+        // Then
+        assertThat(context.sessionSampleRate).isEqualTo(RumContext.FULL_SESSION_SAMPLE_RATE)
+    }
+
     @Test
     fun `M set TRACKED W renewSession() {sampler returns true}`(forge: Forge) {
         // Given

features/dd-sdk-android-trace/api/apiSurface

@@ -22,6 +22,8 @@ open class com.datadog.android.trace.DeterministicTraceSampler : com.datadog.and
   constructor(() -> Float)
   constructor(Float)
   constructor(Double)
+  override fun sample(com.datadog.android.trace.api.span.DatadogSpan): Boolean
+  DEPRECATED fun getSampleRate(com.datadog.android.trace.api.span.DatadogSpan): Float
 annotation com.datadog.android.trace.ExperimentalTraceApi
 object com.datadog.android.trace.GlobalDatadogTracer
   fun registerIfAbsent(com.datadog.android.trace.api.tracer.DatadogTracer): Boolean

features/dd-sdk-android-trace/api/dd-sdk-android-trace.api

@@ -34,6 +34,9 @@ public class com/datadog/android/trace/DeterministicTraceSampler : com/datadog/a
 	public fun <init> (D)V
 	public fun <init> (F)V
 	public fun <init> (Lkotlin/jvm/functions/Function0;)V
+	public final fun getSampleRate (Lcom/datadog/android/trace/api/span/DatadogSpan;)F
+	public fun sample (Lcom/datadog/android/trace/api/span/DatadogSpan;)Z
+	public synthetic fun sample (Ljava/lang/Object;)Z
 }
 
 public abstract interface annotation class com/datadog/android/trace/ExperimentalTraceApi : java/lang/annotation/Annotation {

features/dd-sdk-android-trace/src/main/kotlin/com/datadog/android/trace/ApmNetworkInstrumentationConfiguration.kt

@@ -234,7 +234,8 @@ class ApmNetworkInstrumentationConfiguration internal constructor(
 
     internal companion object {
         internal const val ALL_IN_SAMPLE_RATE: Double = 100.0
-        internal const val DEFAULT_TRACE_SAMPLE_RATE: Float = 100f
+        private const val DEFAULT_TRACE_SAMPLE_RATE: Float = 100f
+
         internal const val NETWORK_REQUESTS_TRACKING_FEATURE_NAME = "Network Requests"
 
         internal fun ApmNetworkInstrumentationConfiguration.createInstrumentation(