[Iceberg AddFiles] Use thread pool to process incoming datafiles

[ahmedabu98]

Improve performance by processing incoming files using a thread pool, allowing a single worker to process files in parallel.

Fixes #38012

[gemini-code-assist]

Summary of Changes

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This pull request significantly enhances the performance of the Iceberg AddFiles operation by introducing parallel processing capabilities. By leveraging a thread pool within the ConvertToDataFile DoFn, the system can now concurrently handle multiple incoming data files, thereby reducing bottlenecks associated with sequential file I/O and metadata operations. This change optimizes resource utilization and accelerates the overall data ingestion process into Iceberg tables.

Highlights

• Asynchronous File Processing: Implemented asynchronous processing of incoming data files within the ConvertToDataFile DoFn to improve performance.
• Thread Pool Integration: Introduced an ExecutorService (thread pool) to parallelize latency-bound operations such as file I/O, catalog lookups, and metadata inference for multiple files concurrently within a single DoFn instance.
• DoFn Lifecycle Management: Refactored the ProcessElement method to submit file processing tasks to the thread pool and added a FinishBundle method to await the completion of all tasks in the current bundle and safely emit results.
• Result Encapsulation: Created a new ProcessResult internal class to encapsulate the outcome of each file's processing, including the SerializableDataFile or any error Row, along with its timestamp and window.

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[chamikaramj]

Thanks!

[chamikaramj]

Probably we should do some experimentation to pick a reasonable default here or base this on similar optimizations done for other I/Os.

[ahmedabu98]

Doing some experiments now

[github-actions]

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[chamikaramj]

Thanks. LGTM.