Add tracing and metrics for blocks delta

src/payload.rs

@@ -43,6 +43,24 @@ impl OpExecutionPayloadEnvelope {
             }
         }
     }
+
+    pub fn tx_count(&self) -> usize {
+        match self {
+            OpExecutionPayloadEnvelope::V3(payload) => payload
+                .execution_payload
+                .payload_inner
+                .payload_inner
+                .transactions
+                .len(),
+            OpExecutionPayloadEnvelope::V4(payload) => payload
+                .execution_payload
+                .payload_inner
+                .payload_inner
+                .payload_inner
+                .transactions
+                .len(),
+        }
+    }
 }
 
 impl From<OpExecutionPayloadEnvelope> for ExecutionPayload {

src/server.rs

@@ -184,6 +184,17 @@ impl RollupBoostServer {
             self.probes.set_health(Health::Healthy);
 
             if let Ok(Some(builder_payload)) = builder_payload {
+                // Record the delta (gas and txn) between the builder and l2 payload
+                let span = tracing::Span::current();
+                span.record(
+                    "gas_delta",
+                    (builder_payload.gas_used() - l2_payload.gas_used()).to_string(),
+                );
+                span.record(
+                    "tx_count_delta",
+                    (builder_payload.tx_count() - l2_payload.tx_count()).to_string(),
+                );
+
                 // If execution mode is set to DryRun, fallback to the l2_payload,
                 // otherwise prefer the builder payload
                 if self.execution_mode().is_dry_run() {
@@ -388,7 +399,9 @@ impl EngineApiServer for RollupBoostServer {
         fields(
             otel.kind = ?SpanKind::Server,
             %payload_id,
-            payload_source
+            payload_source,
+            gas_delta,
+            tx_count_delta,
         )
     )]
     async fn get_payload_v3(
@@ -436,7 +449,9 @@ impl EngineApiServer for RollupBoostServer {
         fields(
             otel.kind = ?SpanKind::Server,
             %payload_id,
-            payload_source
+            payload_source,
+            gas_delta,
+            tx_count_delta,
         )
     )]
     async fn get_payload_v4(

src/tracing.rs

@@ -58,6 +58,34 @@ impl SpanProcessor for MetricsSpanProcessor {
             ])
             .collect::<Vec<_>>();
 
+        // 0 = no difference in gas build via builder vs l2
+        // > 0 = gas used by builder block is greater than l2 block
+        // < 0 = gas used by l2 block is greater than builder block
+        let gas_delta = span
+            .attributes
+            .iter()
+            .find(|attr| attr.key.as_str() == "gas_delta")
+            .map(|attr| attr.value.as_str().to_string());
+
+        if let Some(gas_delta) = gas_delta {
+            histogram!("block_building_gas_delta", &labels)
+                .record(gas_delta.parse::<u64>().unwrap_or_default() as f64);
+        }
+
+        // 0 = no difference in tx count build via builder vs l2
+        // > 0 = num txs in builder block is greater than l2 block
+        // < 0 = num txs in l2 block is greater than builder block
+        let tx_count_delta = span
+            .attributes
+            .iter()
+            .find(|attr| attr.key.as_str() == "tx_count_delta")
+            .map(|attr| attr.value.as_str().to_string());
+
+        if let Some(tx_count_delta) = tx_count_delta {
+            histogram!("block_building_tx_count_delta", &labels)
+                .record(tx_count_delta.parse::<u64>().unwrap_or_default() as f64);
+        }
+
         histogram!(format!("{}_duration", span.name), &labels).record(duration);
     }