Sample on root span level

Author: sentrivana

MIGRATION_GUIDE.md

@@ -11,6 +11,7 @@ Looking to upgrade from Sentry SDK 2.x to 3.x? Here's a comprehensive list of wh
 - The SDK now supports Python 3.7 and higher.
 - `sentry_sdk.start_span` now only takes keyword arguments.
 - `sentry_sdk.start_span` no longer takes an explicit `span` argument.
+- The `sampled` argument of `sentry_sdk.start_span` is only taken into account for root spans (previously known as transactions).
 - The `Span()` constructor does not accept a `hub` parameter anymore.
 - `Span.finish()` does not accept a `hub` parameter anymore.
 - The `Profile()` constructor does not accept a `hub` parameter anymore.

sentry_sdk/integrations/opentelemetry/sampler.py

@@ -120,20 +120,28 @@ def should_sample(
         if not has_tracing_enabled(client.options):
             return dropped_result(parent_span_context, attributes)
 
+        has_parent = parent_span_context.is_valid
+        is_root_span = not has_parent or parent_span_context.is_remote
+
         # Explicit sampled value provided at start_span
         if attributes.get(SentrySpanAttribute.CUSTOM_SAMPLED) is not None:
-            sample_rate = float(attributes[SentrySpanAttribute.CUSTOM_SAMPLED])
-            if sample_rate > 0:
-                return sampled_result(parent_span_context, attributes, sample_rate)
+            if is_root_span:
+                sample_rate = float(attributes[SentrySpanAttribute.CUSTOM_SAMPLED])
+                if sample_rate > 0:
+                    return sampled_result(parent_span_context, attributes, sample_rate)
+                else:
+                    return dropped_result(parent_span_context, attributes)
             else:
-                return dropped_result(parent_span_context, attributes)
+                logger.debug(
+                    f"[Tracing] Ignoring sampled param for non-root span {name}"
+                )
 
         sample_rate = None
 
         # Check if there is a traces_sampler
         # Traces_sampler is responsible to check parent sampled to have full transactions.
         has_traces_sampler = callable(client.options.get("traces_sampler"))
-        if has_traces_sampler:
+        if is_root_span and has_traces_sampler:
             sampling_context = {
                 "transaction_context": {
                     "name": name,
@@ -161,8 +169,7 @@ def should_sample(
             return dropped_result(parent_span_context, attributes)
 
         # Down-sample in case of back pressure monitor says so
-        # TODO: this should only be done for transactions (aka root spans)
-        if client.monitor:
+        if is_root_span and client.monitor:
             sample_rate /= 2**client.monitor.downsample_factor
 
         # Roll the dice on sample rate