feat(spooler): Add metric to track serialization performance (#4135)

relay-server/src/services/buffer/envelope_stack/sqlite.rs

@@ -97,7 +97,9 @@ impl SqliteEnvelopeStack {
 
         // We convert envelopes into a format which simplifies insertion in the store. If an
         // envelope can't be serialized, we will not insert it.
-        let envelopes = envelopes.iter().filter_map(|e| e.as_ref().try_into().ok());
+        let envelopes = relay_statsd::metric!(timer(RelayTimers::BufferEnvelopesSerialization), {
+            envelopes.iter().filter_map(|e| e.as_ref().try_into().ok())
+        });
 
         // When early return here, we are acknowledging that the elements that we popped from
         // the buffer are lost in case of failure. We are doing this on purposes, since if we were

relay-server/src/statsd.rs

@@ -538,6 +538,8 @@ pub enum RelayTimers {
     BufferPop,
     /// Timing in milliseconds for the time it takes for the buffer to drain its envelopes.
     BufferDrain,
+    /// Timing in milliseconds for the time it takes for the envelopes to be serialized.
+    BufferEnvelopesSerialization,
 }
 
 impl TimerMetric for RelayTimers {
@@ -586,6 +588,7 @@ impl TimerMetric for RelayTimers {
             RelayTimers::BufferPeek => "buffer.peek.duration",
             RelayTimers::BufferPop => "buffer.pop.duration",
             RelayTimers::BufferDrain => "buffer.drain.duration",
+            RelayTimers::BufferEnvelopesSerialization => "buffer.envelopes_serialization",
         }
     }
 }