Predefine Vector Capacity for LogRecord Attributes (#1908)

Author: lalitb

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            | 371 ns      |
+    | ot_layer_enabled            | 305 ns      |
 */
 
 use async_trait::async_trait;

opentelemetry-sdk/src/logs/log_emitter.rs

@@ -40,6 +40,7 @@ pub struct LoggerProvider {
 
 /// Default logger name if empty string is provided.
 const DEFAULT_COMPONENT_NAME: &str = "rust.opentelemetry.io/sdk/logger";
+const PREALLOCATED_ATTRIBUTE_CAPACITY: usize = 8;
 
 impl opentelemetry::logs::LoggerProvider for LoggerProvider {
     type Logger = Logger;
@@ -246,7 +247,11 @@ impl opentelemetry::logs::Logger for Logger {
     type LogRecord = LogRecord;
 
     fn create_log_record(&self) -> Self::LogRecord {
-        LogRecord::default()
+        // Reserve attributes memory for perf optimization. This may change in future.
+        LogRecord {
+            attributes: Some(Vec::with_capacity(PREALLOCATED_ATTRIBUTE_CAPACITY)),
+            ..Default::default()
+        }
     }
 
     /// Emit a `LogRecord`.

stress/src/logs.rs

@@ -3,7 +3,7 @@
     OS: Ubuntu 22.04.3 LTS (5.15.146.1-microsoft-standard-WSL2)
     Hardware: AMD EPYC 7763 64-Core Processor - 2.44 GHz, 16vCPUs,
     RAM: 64.0 GB
-    53 M/sec
+    69 M/sec
 */
 
 use opentelemetry_appender_tracing::layer;