Add metric for write EAGAIN failures

src/connection.cpp

@@ -26,6 +26,11 @@ thread_local auto bytes_written =
     metric::create_counter("weaseldb_bytes_written_total",
                            "Total number of bytes written to clients")
         .create({});
+thread_local auto write_eagain_failures =
+    metric::create_counter(
+        "weaseldb_write_eagain_failures_total",
+        "Total number of write operations that failed with EAGAIN")
+        .create({});
 } // namespace
 
 // Static thread-local storage for iovec buffer
@@ -130,6 +135,8 @@ bool Connection::writeBytes() {
           continue; // Standard practice: retry on signal interruption
         }
         if (errno == EAGAIN) {
+          // Increment EAGAIN failure metric
+          write_eagain_failures.inc();
           // Increment bytes written metric before returning
           if (total_bytes_written > 0) {
             bytes_written.inc(total_bytes_written);