Implements the Delta Lake source with support for splitting

[chamikaramj]

Adds a DeltaReadTasksDoFn, that groups files into 1 GB DeltaReadTasks.

Adds a SDF, DeltaSourceDoFn that implements the functionality for reading a PCollection of DeltaReadTasks.

Adds a RangeTracker, DeltaReadTaskTracker, that can be used to track a range of row groups that belong to a given DeltaReadTask.

Adds BeamParquetHandler that implements the Delta Kernel Engine API ParquetHandler to perform reading and splitting considering correct row group ranges.

For additional context, please see the design https://s.apache.org/beam-delta-lake-source.

This fixes #38551.

This fixes #38552.

This fixes #38553.

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request implements a native Delta Lake source for Apache Beam, allowing users to read Delta tables efficiently. It introduces a task-based approach to file reading, grouping files into 1GB tasks, and leverages Splittable DoFns to enable dynamic work rebalancing at the row-group level. The implementation integrates with the Delta Kernel Engine and includes comprehensive testing for serialization and data reading.

Highlights

• Delta Lake Source Implementation: Implemented a new Delta Lake source in Beam, enabling efficient reading and splitting of Delta tables.
• Splittable DoFn Support: Added DeltaSourceDoFn and DeltaReadTaskTracker to support dynamic work rebalancing across Parquet row groups.
• Delta Kernel Integration: Integrated with the Delta Kernel Engine API via BeamParquetHandler and BeamEngine to facilitate reading and splitting.
• Serialization Utilities: Introduced SerializableRow and SerializableStructType to handle data serialization across worker nodes.

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[gemini-code-assist]

Code Review

This pull request implements Delta Lake reading capabilities within the Apache Beam Java SDK. It introduces a custom BeamEngine and BeamParquetHandler to integrate Delta Kernel's engine with Beam's RestrictionTracker for row group claiming. It also adds CreateReadTasksDoFn to plan read tasks, DeltaSourceDoFn as a splittable DoFn to process logical reads, and serialization wrappers (SerializableRow, SerializableStructType). Feedback focuses on performance optimizations—such as caching Hadoop configurations and task metadata to avoid duplicate Parquet footer reads—and resource safety improvements to ensure closeable iterators are properly closed even when exceptions occur.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.08%. Comparing base (eb29f86) to head (6a52b00).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #38706      +/-   ##
============================================
+ Coverage     56.40%   58.08%   +1.67%     
- Complexity     3803    12943    +9140     
============================================
  Files          1316     2511    +1195     
  Lines        181666   262251   +80585     
  Branches       2586    10655    +8069     
============================================
+ Hits         102464   152319   +49855     
- Misses        76359   104230   +27871     
- Partials       2843     5702    +2859     

Flag	Coverage Δ
java	64.17% <ø> (-8.20%)	⬇️

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