What logs and metrics are most useful for Distributed tracing?

         $traceId,
            "span_id" => $spanId,
            "service_name" => "OrderService",
            "timestamp" => time(),
            "message" => "Process started for order ID: 12345"
        ]);
        
        // Collecting performance metrics like response time
        $startTime = microtime(true);
        
        // Simulate a process (e.g., a database call)
        sleep(1); // Simulates delay
        
        $endTime = microtime(true);
        $responseTime = $endTime - $startTime; // Calculate response time
        
        // Log the completion of the process
        logEvent("PROCESS_END", [
            "trace_id" => $traceId,
            "span_id" => $spanId,
            "service_name" => "OrderService",
            "response_time" => $responseTime,
            "timestamp" => time(),
            "message" => "Process completed for order ID: 12345"
        ]);
        
        function logEvent($eventType, $data) {
            // Function to send logs to a centralized logging system
            // Here, you would typically send data to a logging service (e.g., ELK, Splunk)
            echo json_encode([$eventType => $data]);
        }
        
        function generateTraceId() {
            return bin2hex(random_bytes(16)); // Generate a random trace ID
        }

        function generateSpanId() {
            return bin2hex(random_bytes(8)); // Generate a random span ID
        }
        ?>