perf: dont attach stacktraces to all events

src/Client.php

@@ -285,6 +285,14 @@ public function getSdkVersion(): string
      */
     private function prepareEvent(Event $event, ?EventHint $hint = null, ?Scope $scope = null): ?Event
     {
+        $sampleRate = $this->options->getSampleRate();
+
+        if (EventType::event() === $event->getType() && $sampleRate < 1 && mt_rand(1, 100) / 100.0 > $sampleRate) {
+            $this->logger->info(\sprintf('The %s will be discarded because it has been sampled.', $this->getEventDescription($event)), ['event' => $event]);
+
+            return null;
+        }
+
         if ($hint !== null) {
             if ($hint->exception !== null && empty($event->getExceptions())) {
                 $this->addThrowableToEvent($event, $hint->exception, $hint);
@@ -314,22 +322,7 @@ private function prepareEvent(Event $event, ?EventHint $hint = null, ?Scope $sco
             $event->setEnvironment($this->options->getEnvironment() ?? Event::DEFAULT_ENVIRONMENT);
         }
 
-        $eventDescription = \sprintf(
-            '%s%s [%s]',
-            $event->getLevel() !== null ? $event->getLevel() . ' ' : '',
-            (string) $event->getType(),
-            (string) $event->getId()
-        );
-
-        $isEvent = EventType::event() === $event->getType();
-        $sampleRate = $this->options->getSampleRate();
-
-        // only sample with the `sample_rate` on errors/messages
-        if ($isEvent && $sampleRate < 1 && mt_rand(1, 100) / 100.0 > $sampleRate) {
-            $this->logger->info(\sprintf('The %s will be discarded because it has been sampled.', $eventDescription), ['event' => $event]);
-
-            return null;
-        }
+        $eventDescription = $this->getEventDescription($event);
 
         $event = $this->applyIgnoreOptions($event, $eventDescription);
 
@@ -368,6 +361,16 @@ private function prepareEvent(Event $event, ?EventHint $hint = null, ?Scope $sco
         return $event;
     }
 
+    private function getEventDescription(Event $event): string
+    {
+        return \sprintf(
+            '%s%s [%s]',
+            $event->getLevel() !== null ? $event->getLevel() . ' ' : '',
+            (string) $event->getType(),
+            (string) $event->getId()
+        );
+    }
+
     /**
      * Checks if an exception should be ignored based on configured patterns.
      * Supports both class hierarchy matching and regex patterns.
@@ -528,6 +531,11 @@ private function addMissingStacktraceToEvent(Event $event): void
             return;
         }
 
+        // Only error events carry a stacktrace, for any other type it would be discarded
+        if ($event->getType() !== EventType::event()) {
+            return;
+        }
+
         // We should not add a stacktrace when the event already has one or contains exceptions
         if ($event->getStacktrace() !== null || !empty($event->getExceptions())) {
             return;

tests/ClientTest.php

@@ -361,6 +361,40 @@ public static function captureEventAttachesStacktraceAccordingToAttachStacktrace
         ];
     }
 
+    /**
+     * @dataProvider captureEventDoesNotAttachStacktraceToNonErrorEventsDataProvider
+     */
+    public function testCaptureEventDoesNotAttachStacktraceToNonErrorEvents(Event $event): void
+    {
+        /** @var TransportInterface&MockObject $transport */
+        $transport = $this->createMock(TransportInterface::class);
+        $transport->expects($this->once())
+                  ->method('send')
+                  ->with($this->callback(static function (Event $event): bool {
+                      return $event->getStacktrace() === null;
+                  }))
+                  ->willReturnCallback(static function (Event $event): Result {
+                      return new Result(ResultStatus::success(), $event);
+                  });
+
+        $client = ClientBuilder::create(['attach_stacktrace' => true])
+                               ->setTransport($transport)
+                               ->getClient();
+
+        $this->assertNotNull($client->captureEvent($event));
+    }
+
+    public static function captureEventDoesNotAttachStacktraceToNonErrorEventsDataProvider(): \Generator
+    {
+        yield 'transaction' => [Event::createTransaction()];
+
+        yield 'check-in' => [Event::createCheckIn()];
+
+        yield 'logs' => [Event::createLogs()];
+
+        yield 'metrics' => [Event::createMetrics()];
+    }
+
     public function testCaptureEventPrefersExplicitStacktrace(): void
     {
         $stacktrace = new Stacktrace([
@@ -652,6 +686,29 @@ public function testProcessEventDiscardsEventWhenSampleRateOptionIsZero(): void
         $client->captureEvent(Event::createEvent());
     }
 
+    public function testProcessEventDoesNotBuildStacktracesWhenEventIsNotSampled(): void
+    {
+        $logger = $this->createMock(LoggerInterface::class);
+        $logger->expects($this->exactly(2))
+               ->method('info')
+               ->with(
+                   new StringMatchesFormatDescription('The event [%s] will be discarded because it has been sampled.'),
+                   $this->callback(static function (array $context): bool {
+                       return $context['event'] instanceof Event
+                           && $context['event']->getExceptions() === []
+                           && $context['event']->getStacktrace() === null;
+                   })
+               );
+
+        $client = ClientBuilder::create(['sample_rate' => 0, 'attach_stacktrace' => true])
+                               ->setTransport($this->createMock(TransportInterface::class))
+                               ->setLogger($logger)
+                               ->getClient();
+
+        $client->captureException(new \Exception('foo'));
+        $client->captureMessage('foo');
+    }
+
     public function testProcessEventCapturesEventWhenSampleRateOptionIsAboveZero(): void
     {
         $transport = $this->createMock(TransportInterface::class);