# Settings for the Log4j Appender instrumentation

| System property                                                                    | Type    | Default | Description                                                                                           |
| ---------------------------------------------------------------------------------- | ------- | ------- | ----------------------------------------------------------------------------------------------------- |
| `otel.instrumentation.log4j-appender.experimental-log-attributes`                  | Boolean | `false` | Enable the capture of experimental span attributes `thread.name` and `thread.id`.                     |
| `otel.instrumentation.log4j-appender.experimental.capture-map-message-attributes`  | Boolean | `false` | Enable the capture of `MapMessage` attributes.                                                        |
| `otel.instrumentation.log4j-appender.experimental.capture-marker-attribute`        | Boolean | `false` | Enable the capture of Log4j markers as attributes.                                                    |
| `otel.instrumentation.log4j-appender.experimental.capture-context-data-attributes` | String  |         | List of context data attributes to capture. Use the wildcard character `*` to capture all attributes. |

[source code attributes]: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/semantic_conventions/span-general.md#source-code-attributes