[Dataflow Streaming] Reuse ByteStringOutputStream buffers in WindmillBag

[arunpandianp]

#33578

Also extracted the Threadlocal logic to a separate ThreadLocalByteStringOutputStream class, which can be used elsewhere.

[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 a significant performance optimization for Dataflow Streaming by implementing a mechanism to reuse ByteStringOutputStream buffers. By centralizing the management of these streams in a thread-local utility, the changes aim to reduce object allocation and improve the efficiency of encoding operations within core Dataflow components like WindmillBag and WindmillStateTagUtil. This should lead to better memory utilization and potentially faster execution for streaming jobs.

Highlights

• New Utility Class: Introduced ThreadLocalByteStringOutputStream, a new utility class designed to manage and reuse ByteStringOutputStream instances on a per-thread basis, reducing object allocation overhead.
• WindmillBag Optimization: The WindmillBag class now leverages the new ThreadLocalByteStringOutputStream for encoding elements when persisting directly, replacing direct instantiation of ByteStringOutputStream.
• WindmillStateTagUtil Refactoring: The WindmillStateTagUtil has been refactored to utilize the new thread-local stream for encoding state keys, streamlining its internal buffer management and removing redundant ThreadLocal logic.
• Performance Improvement: These changes aim to improve performance in Dataflow Streaming by reducing memory allocations and garbage collection pressure through the reuse of ByteStringOutputStream buffers.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[github-actions]

Stopping reviewer notifications for this pull request: review requested by someone other than the bot, ceding control. If you'd like to restart, comment assign set of reviewers

[arunpandianp]

Run Java PreCommit

[scwhittle]

Thanks for putting up with my comments :)