Sample on root span level

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.
+- `sentry_sdk.start_span` now accepts the `sampled` argument. It is however 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/consts.py

@@ -31,3 +31,6 @@ class SentrySpanAttribute:
     SOURCE = "sentry.source"
     CONTEXT = "sentry.context"
     CUSTOM_SAMPLED = "sentry.custom_sampled"  # used for saving start_span(sampled=X)
+    CUSTOM_PARENT_SAMPLED = (
+        "sentry.custom_parent_sampled"  # used for saving start_span(parent_sampled=X)
+    )

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)
 
+        # parent_span_context.is_valid means this span has a parent, remote or local
+        is_root_span = not parent_span_context.is_valid 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,
@@ -146,7 +154,11 @@ def should_sample(
 
         else:
             # Check if there is a parent with a sampling decision
-            parent_sampled = get_parent_sampled(parent_span_context, trace_id)
+            parent_sampled = attributes.get(SentrySpanAttribute.CUSTOM_PARENT_SAMPLED)
+
+            if parent_sampled is None:
+                parent_sampled = get_parent_sampled(parent_span_context, trace_id)
+
             if parent_sampled is not None:
                 sample_rate = parent_sampled
             else:
@@ -161,8 +173,7 @@ 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

sentry_sdk/tracing.py

@@ -1212,6 +1212,7 @@ def __init__(
         attributes=None,  # type: OTelSpanAttributes
         only_if_parent=False,  # type: bool
         otel_span=None,  # type: Optional[OtelSpan]
+        parent_sampled=None,  # type: Optional[bool]
         **_,  # type: dict[str, object]
     ):
         # type: (...) -> None
@@ -1252,6 +1253,10 @@ def __init__(
                 attributes[SentrySpanAttribute.OP] = op
                 if sampled is not None:
                     attributes[SentrySpanAttribute.CUSTOM_SAMPLED] = sampled
+                if parent_sampled is not None:
+                    attributes[SentrySpanAttribute.CUSTOM_PARENT_SAMPLED] = (
+                        parent_sampled
+                    )
 
                 self._otel_span = tracer.start_span(
                     span_name, start_time=start_timestamp, attributes=attributes

tests/tracing/test_sampling.py

@@ -24,16 +24,16 @@ def test_sampling_decided_only_for_transactions(sentry_init, capture_events):
 
 
 @pytest.mark.parametrize("sampled", [True, False])
-def test_nested_transaction_sampling_override(sentry_init, sampled):
+def test_nested_span_sampling_override(sentry_init, sampled):
     sentry_init(traces_sample_rate=1.0)
 
-    with start_transaction(name="outer", sampled=sampled) as outer_transaction:
-        assert outer_transaction.sampled is sampled
-        with start_transaction(
-            name="inner", sampled=(not sampled)
-        ) as inner_transaction:
-            assert inner_transaction.sampled is not sampled
-        assert outer_transaction.sampled is sampled
+    with start_span(name="outer", sampled=sampled) as outer_span:
+        assert outer_span.sampled is sampled
+        with start_span(name="inner", sampled=(not sampled)) as inner_span:
+            # won't work because the child span inherits the sampling decision
+            # from the parent
+            assert inner_span.sampled is sampled
+        assert outer_span.sampled is sampled
 
 
 def test_no_double_sampling(sentry_init, capture_events):
@@ -177,10 +177,8 @@ def test_inherits_parent_sampling_decision_when_traces_sampler_undefined(
     mock_random_value = 0.25 if parent_sampling_decision is False else 0.75
 
     with mock.patch.object(random, "random", return_value=mock_random_value):
-        transaction = start_transaction(
-            name="dogpark", parent_sampled=parent_sampling_decision
-        )
-        assert transaction.sampled is parent_sampling_decision
+        span = start_span(name="dogpark", parent_sampled=parent_sampling_decision)
+        assert span.sampled is parent_sampling_decision
 
 
 @pytest.mark.parametrize("parent_sampling_decision", [True, False])