Appender-Tracing benchmark to pass message as attribute - 10% faster

opentelemetry-appender-tracing/benches/logs.rs

@@ -10,7 +10,7 @@
     | noop_layer_disabled         | 12 ns       |
     | noop_layer_enabled          | 25 ns       |
     | ot_layer_disabled           | 19 ns       |
-    | ot_layer_enabled            | 280 ns      |
+    | ot_layer_enabled            | 250 ns      |
 */
 
 use async_trait::async_trait;
@@ -116,7 +116,7 @@ fn benchmark_no_subscriber(c: &mut Criterion) {
                 name = "CheckoutFailed",
                 book_id = "12345",
                 book_title = "Rust Programming Adventures",
-                "Unable to process checkout."
+                message = "Unable to process checkout."
             );
         });
     });
@@ -142,7 +142,7 @@ fn benchmark_with_ot_layer(c: &mut Criterion, enabled: bool, bench_name: &str) {
                     name = "CheckoutFailed",
                     book_id = "12345",
                     book_title = "Rust Programming Adventures",
-                    "Unable to process checkout."
+                    message = "Unable to process checkout."
                 );
             });
         });

opentelemetry-appender-tracing/examples/basic.rs

@@ -18,6 +18,6 @@ fn main() {
     let layer = layer::OpenTelemetryTracingBridge::new(&provider);
     tracing_subscriber::registry().with(layer).init();
 
-    error!(name: "my-event-name", target: "my-system", event_id = 20, user_name = "otel", user_email = "otel@opentelemetry.io");
+    error!(name: "my-event-name", target: "my-system", event_id = 20, user_name = "otel", user_email = "otel@opentelemetry.io", message = "This is an example message");
     let _ = provider.shutdown();
 }

opentelemetry-appender-tracing/src/layer.rs

@@ -93,6 +93,13 @@ impl<'a, LR: LogRecord> tracing::field::Visit for EventVisitor<'a, LR> {
         if is_duplicated_metadata(field.name()) {
             return;
         }
+        //TODO: Consider special casing "message" to populate body and document
+        // to users to use message field for log message, to avoid going to the
+        // record_debug, which has dyn dispatch, string allocation and
+        // formatting cost.
+
+        //TODO: Fix heap allocation. Check if lifetime of &str can be used
+        // to optimize sync exporter scenario.
         self.log_record
             .add_attribute(Key::new(field.name()), AnyValue::from(value.to_owned()));
     }
@@ -163,8 +170,9 @@ where
         #[cfg(not(feature = "experimental_metadata_attributes"))]
         let meta = event.metadata();
 
-        //let mut log_record: LogRecord = LogRecord::default();
         let mut log_record = self.logger.create_log_record();
+
+        // TODO: Fix heap allocation
         log_record.set_target(meta.target().to_string());
         log_record.set_event_name(meta.name());
         log_record.set_severity_number(severity_of_level(meta.level()));