Merge pull request #6927 from lgayhardt/patch-79

update tracing

Author: prmerger-automator[bot]

articles/machine-learning/prompt-flow/how-to-develop-flow.md

@@ -128,6 +128,15 @@ After the flow run completes, you can select **View outputs** to check all histo
 
 :::image type="content" source="./media/how-to-develop-flow/authoring-test-result.png" alt-text="Screenshot of flow test result." lightbox ="./media/how-to-develop-flow/authoring-test-result.png":::
 
+#### Trace
+
+Tracing is disabled by default, to enable tracing you need to set the environment variable `PF_DISABLE_TRACING` to `false`. One way you can do this is by adding the following to the python node:
+
+```python
+import os
+os.environ["PF_DISABLE_TRACING"] = "false"
+```
+
 Select the **Trace** tab on the **Outputs** screen to see a graph that provides information about the duration and associated token cost of the flow. Select **flow** under **node name** to see detailed flow overview information in the right pane.
 
 Expand **flow** and select any step to see detailed information for that step. You can see the duration of each node execution in the span tree. For more information, see [Trace Span Specification](https://microsoft.github.io/promptflow/reference/trace-span-spec-reference.html).