instr(server): Measure nested span count (#4221)

relay-server/src/services/projects/cache/project.rs

@@ -9,6 +9,7 @@ use crate::envelope::ItemType;
 use crate::services::outcome::{DiscardReason, Outcome};
 use crate::services::projects::cache::state::SharedProject;
 use crate::services::projects::project::ProjectState;
+use crate::statsd::RelayTimers;
 use crate::utils::{CheckLimits, Enforcement, EnvelopeLimiter, ManagedEnvelope};
 
 /// A loaded project.
@@ -90,7 +91,9 @@ impl<'a> Project<'a> {
         // If we can extract spans from the event, we want to try and count the number of nested
         // spans to correctly emit negative outcomes in case the transaction itself is dropped.
         if check_nested_spans {
-            sync_spans_to_enforcement(&envelope, &mut enforcement);
+            relay_statsd::metric!(timer(RelayTimers::CheckNestedSpans), {
+                sync_spans_to_enforcement(&envelope, &mut enforcement);
+            });
         }
 
         enforcement.apply_with_outcomes(&mut envelope);

relay-server/src/statsd.rs

@@ -553,6 +553,8 @@ pub enum RelayTimers {
     BufferEnvelopesSerialization,
     /// Timing in milliseconds to the time it takes to read an HTTP body.
     BodyReadDuration,
+    /// Timing in milliseconds to count spans in a serialized transaction payload.
+    CheckNestedSpans,
 }
 
 impl TimerMetric for RelayTimers {
@@ -605,6 +607,7 @@ impl TimerMetric for RelayTimers {
             RelayTimers::BufferDrain => "buffer.drain.duration",
             RelayTimers::BufferEnvelopesSerialization => "buffer.envelopes_serialization",
             RelayTimers::BodyReadDuration => "requests.body_read.duration",
+            RelayTimers::CheckNestedSpans => "envelope.check_nested_spans",
         }
     }
 }