WIP

Author: cleptric

src/State/Hub.php

@@ -269,6 +269,7 @@ public function startTransaction(TransactionContext $context, array $customSampl
         $samplingContext->setAdditionalContext($customSamplingContext);
 
         $sampleSource = 'context';
+        $sampleRand = $context->getMetadata()->getSampleRand();
 
         if ($transaction->getSampled() === null) {
             $tracesSampler = $options->getTracesSampler();
@@ -278,12 +279,17 @@ public function startTransaction(TransactionContext $context, array $customSampl
 
                 $sampleSource = 'config:traces_sampler';
             } else {
-                $sampleRate = $this->getSampleRate(
-                    $samplingContext->getParentSampled(),
-                    $options->getTracesSampleRate() ?? 0
-                );
-
-                $sampleSource = $samplingContext->getParentSampled() ? 'parent' : 'config:traces_sample_rate';
+                $parentSampleRate = (float) $context->getMetadata()->getDynamicSamplingContext()->get('sample_rate');
+                if ($parentSampleRate !== null) {
+                    $sampleRate = $parentSampleRate;
+                    $sampleSource = 'parent';
+                } else {
+                    $sampleRate = $this->getSampleRate(
+                        $samplingContext->getParentSampled(),
+                        $options->getTracesSampleRate() ?? 0
+                    );
+                    $sampleSource = $samplingContext->getParentSampled() ? 'parent' : 'config:traces_sample_rate';
+                }
             }
 
             if (!$this->isValidSampleRate($sampleRate)) {
@@ -294,6 +300,7 @@ public function startTransaction(TransactionContext $context, array $customSampl
                 return $transaction;
             }
 
+            // TODO Why are we doing this?
             $transaction->getMetadata()->setSamplingRate($sampleRate);
 
             if ($sampleRate === 0.0) {

src/Tracing/DynamicSamplingContext.php

@@ -199,6 +199,7 @@ public static function fromOptions(Options $options, Scope $scope): self
     {
         $samplingContext = new self();
         $samplingContext->set('trace_id', (string) $scope->getPropagationContext()->getTraceId());
+        $samplingContext->set('sample_rand', (string) $scope->getPropagationContext()->getSampleRand());
 
         if ($options->getTracesSampleRate() !== null) {
             $samplingContext->set('sample_rate', (string) $options->getTracesSampleRate());

src/Tracing/PropagationContext.php

@@ -33,6 +33,11 @@ final class PropagationContext
      */
     private $dynamicSamplingContext;
 
+        /**
+     * @var float|null
+     */
+    private $sampleRand;
+
     private function __construct()
     {
     }
@@ -46,6 +51,9 @@ public static function fromDefaults(): self
         $context->parentSpanId = null;
         $context->dynamicSamplingContext = null;
 
+        // TODO check if this is precise enough
+        $context->sampleRand = round(mt_rand(0, mt_getrandmax() - 1) / mt_getrandmax(), 6);
+
         return $context;
     }
 
@@ -159,6 +167,7 @@ public function setDynamicSamplingContext(DynamicSamplingContext $dynamicSamplin
         return $this;
     }
 
+    // TODO add same logic as in TransactionContext
     private static function parseTraceparentAndBaggage(string $traceparent, string $baggage): self
     {
         $context = self::fromDefaults();

src/Tracing/TransactionContext.php

@@ -199,12 +199,20 @@ private static function parseTraceAndBaggage(string $sentryTrace, string $baggag
         }
 
         if ($samplingContext->has('sample_rand')) {
+            // TODO check for 1e13 etc.
             $context->getMetadata()->setSampleRand((float) $samplingContext->get('sample_rand'));
         } else {
             if ($samplingContext->has('sample-rate') && $context->parentSampled !== null) {
-                $context->getMetadata()->setSampleRand(1);
+                if ($context->parentSampled === true) {
+                    // [0, rate)
+                    $context->getMetadata()->setSampleRand(round(mt_rand(0, mt_getrandmax() - 1) / mt_getrandmax() * $samplingContext->get('sample-rate'), 6));
+                } else {
+                    // [rate, 1]
+                    $context->getMetadata()->setSampleRand(round(mt_rand(0, mt_getrandmax() - 1) / mt_getrandmax() * (1 - $samplingContext->get('sample-rate')) + $samplingContext->get('sample-rate'), 6));  
+                }
             } elseif ($context->parentSampled !== null) {
-                $context->getMetadata()->setSampleRand(1);
+                // [0, 1)
+                $context->getMetadata()->setSampleRand(round(mt_rand(0, mt_getrandmax() - 1) / mt_getrandmax(), 6));
             }
         }
 

src/Tracing/TransactionMetadata.php

@@ -42,7 +42,8 @@ public function __construct(
         $this->dynamicSamplingContext = $dynamicSamplingContext;
         $this->source = $source ?? TransactionSource::custom();
 
-        $this->sampleRand = round(mt_rand(0, mt_getrandmax() - 1) / mt_getrandmax(), 2);
+        // TODO check if this is precise enough
+        $this->sampleRand = round(mt_rand(0, mt_getrandmax() - 1) / mt_getrandmax(), 6);
     }
 
     /**