kevinjqliu commented on issue #542: URL: https://github.com/apache/iceberg-python/issues/542#issuecomment-2016892964
I asked an AI for answers... #### Prompt ``` theres a bug in @pyarrow.py function `project_table` and `_task_to_table` can you find the bug? it has to do with concurrency ``` #### Answer The bug in the [project_table](https://github.com/apache/iceberg-python/blob/6989b92c2d449beb9fe4817c64f619ea5bfc81dc/pyiceberg/io/pyarrow.py#L1044) and [_task_to_table](https://github.com/apache/iceberg-python/blob/6989b92c2d449beb9fe4817c64f619ea5bfc81dc/pyiceberg/io/pyarrow.py#L941) functions within [pyiceberg/io/pyarrow.py](https://github.com/apache/iceberg-python/blob/6989b92c2d449beb9fe4817c64f619ea5bfc81dc/pyiceberg/io/pyarrow.py#L1) related to concurrency likely stems from the handling of futures and the potential for race conditions or incorrect handling of asynchronous execution. Specifically, the issue could be related to how the futures are managed and how results are collected from these futures. In the `project_table` function, futures are created and submitted to an executor for asynchronous execution of `_task_to_table` tasks. The results of these futures are then collected and processed. However, there are a few areas where concurrency issues could arise: 1. **Early Termination and Future Cancellation**: The code attempts to stop early if a limit on the number of records is satisfied (`if limit is not None and sum(row_counts) >= limit:`). After this check, it cancels any remaining futures that have not yet completed. This approach assumes that the futures are executed and completed in a specific order, which might not always be the case. Futures could complete in any order, and cancelling futures prematurely could lead to incomplete processing or missed data. ```python if limit is not None: _ = [f.cancel() for f in futures if not f.done()] ``` 2. **Inconsistent Ordering and Result Collection**: The futures are stored in a `SortedList` based on their submission order to ensure consistent ordering. However, the actual execution order of these futures is not guaranteed, and relying on the submission order for processing results could lead to inconsistencies, especially if the task execution times vary significantly. ```python completed_futures: SortedList[Future[pa.Table]] = SortedList(iterable=[], key=lambda f: futures_index[f]) ``` 3. **Shared State Management (`row_counts`)**: The `row_counts` list is shared among all tasks and is used to determine when the limit is reached. However, this shared state is updated after each future completes, without proper synchronization. This could lead to race conditions where multiple threads attempt to update the `row_counts` list simultaneously, leading to incorrect counts. ```python row_counts.append(len(arrow_table)) ``` To address these issues, consider the following: - **Reevaluate Early Termination Logic**: Ensure that the logic for early termination and future cancellation correctly accounts for the asynchronous nature of task execution. It may be safer to collect and process all results before deciding whether the limit has been reached, rather than cancelling futures prematurely. - **Synchronization of Shared State**: If shared state (like `row_counts`) must be updated by multiple tasks, ensure proper synchronization to prevent race conditions. This could involve using thread-safe data structures or explicit locking mechanisms. - **Ordering of Results**: If the order of results is important, consider collecting all future results first and then sorting or processing them based on the desired criteria, rather than relying on the order of future submission. These suggestions aim to mitigate potential concurrency issues in the `project_table` and `_task_to_table` functions, ensuring correct and consistent processing of tasks in an asynchronous environment. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
