fix(sessions): skip unnecessary FOR UPDATE lock on app/user state rows

[giulio-leone]

The database session service currently takes FOR UPDATE locks on app and user state rows even when there are no deltas to write. This causes unnecessary lock contention under concurrent requests.

This PR skips the lock acquisition when there are no state deltas to persist.

Supersedes #4656 (closed due to CLA issue, now resolved).

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

[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 significantly enhances the concurrency and performance of the database session service by optimizing the acquisition of FOR UPDATE locks. By pre-analyzing state changes, the system now intelligently skips unnecessary locks on app and user state rows, thereby reducing contention and improving the efficiency of concurrent append_event operations.

Highlights

• Optimized Database Locking: Introduced logic to pre-analyze state deltas within the append_event function, allowing the system to determine if app or user state modifications are actually present before attempting to acquire FOR UPDATE locks.
• Reduced Lock Contention: Enabled conditional acquisition of FOR UPDATE locks on app and user state rows, preventing unnecessary serialization of concurrent append_event calls when no app or user state changes are required.
• Improved Robustness: Added a null check to the session state update logic, ensuring state_deltas exists before attempting to access its 'session' key, preventing potential errors.

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Changelog

• src/google/adk/sessions/database_session_service.py
  • Added new code to the append_event method to extract and analyze state deltas, determining if 'app' or 'user' scoped state changes are present.
  • Modified the condition for updating session-scoped state to include a null check for state_deltas, making the operation more robust.

Activity

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[adk-bot]

Response from ADK Triaging Agent

Hello @giulio-leone, thank you for your contribution!

Could you please add a testing plan section to your PR description to describe how you tested these changes? This will help the reviewers to better understand and verify your fix.

You can find more information about the contribution guidelines here: https://github.com/google/adk-python/blob/main/CONTRIBUTING.md#requirement-for-prs

Thanks!

[gemini-code-assist]

Code Review

This pull request introduces a valuable performance optimization by skipping unnecessary FOR UPDATE locks on app and user state rows during event appends when there are no state deltas. The approach of pre-analyzing state deltas to conditionally acquire locks is sound and well-implemented. The accompanying changes and tests are appropriate. I have one minor suggestion to improve code clarity by removing a redundant check.