Trace data loss in worker processes

Weave uploads trace data in background threads to minimize impact on your application’s performance. However, when using a multiprocessing or task queue system or a worker processes like Celery, Weave loses trace data if the worker process exits before background threads finish uploading traces.

To prevent data loss in worker processes, you must ensure that background uploads complete by calling client.flush() or client.finish() before the worker task completes. This helps when working in short‑lived environments like AWS Lambda, Google Cloud Run, or notebooks that exit right after execution.

These methods have different purposes:

• weave.flush(): Simple, silent flushing. Recommended when Weave is integrated into worker processes or CI environments.
• weave.finish(): Includes progress feedback with a progress bar or status callbacks. Recommended for interactive scripts or notebooks.

Both methods block until all background uploads complete, ensuring no trace data is lost when the worker process exits.

The following example demonstrates client.finish():

from celery import Celery
import weave

app = Celery('tasks')

@app.task
def process_task(input_data):
    weave.init("your-team-name/your-project-name")

    try:
        # Your task logic that creates traces
        result = your_processing_function(input_data)

        # Ensure all traces are uploaded before task completes
        weave.finish()

        return result
    finally:
        pass

You can also use the with context manager to automatically call weave.finish() on exit:

with weave.init("your-team-name/your-project-name") as client:
    result = your_processing_function(input_data)

    return result

You can also improve the performance of your application using weave.flush(). See Flushing for more information.

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Trace Data Performance