[Dataflow Streaming] Reuse proto builders on hot path to reduce GC overhead

[arunpandianp]

#33578

Noticed it while debugging long GC on a high cardinality job.

[arunpandianp]

R: @scwhittle

[gemini-code-assist]

Summary of Changes

Hello @arunpandianp, 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 introduces targeted performance optimizations for Dataflow Streaming by strategically reusing Protocol Buffer builders in critical 'hot path' code sections. By initializing and clearing builders instead of creating new ones for each operation, the changes aim to significantly reduce garbage collection overhead, particularly in high-cardinality jobs, leading to improved stability and efficiency in data processing.

Highlights

• WindmillSink Optimization: The WindmillStreamWriter now reuses Windmill.Message.Builder and Windmill.OutputMessageBundle.Builder instances. Instead of creating new builders for each message or bundle, existing builders are cleared and re-populated, significantly reducing object allocation and subsequent garbage collection overhead during message construction.
• GetWorkResponseChunkAssembler Optimization: The GetWorkResponseChunkAssembler has been updated to reuse a WorkItem.Builder instance. This change avoids repeated creation of WorkItem.Builder objects when parsing incoming work item data, contributing to lower GC pressure during the assembly of work items.

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[arunpandianp]

/gemini review

[gemini-code-assist]

Code Review

This pull request aims to reduce garbage collection overhead by reusing Protobuf builders in performance-sensitive code paths. The changes in WindmillSink.java and GetWorkResponseChunkAssembler.java correctly apply this optimization. However, I've identified a potential issue in GetWorkResponseChunkAssembler.java where the change in parsing logic alters exception handling for malformed messages, which could lead to uncaught runtime exceptions. I've provided a detailed comment and a code suggestion to address this while preserving the performance improvements.

[arunpandianp]

/gemini review

[gemini-code-assist]

Code Review

This pull request aims to reduce GC overhead on hot paths by reusing protobuf builders, which is a great optimization. The changes in WindmillSink.java correctly implement this pattern for Message.Builder and OutputMessageBundle.Builder. Similarly, GetWorkResponseChunkAssembler.java is updated to reuse a WorkItem.Builder. However, I've found a critical issue in the exception handling in GetWorkResponseChunkAssembler.java that will likely cause a compilation failure. Please see my detailed comment.