perf(country): prevent cache stampede by caching in-flight requests #46
Conversation
- Introduce futures to hold in-progress aggregation requests - Modify getCachedEventCountries and getCachedHeadquarterCountries to check for in-progress fetches - Refactor aggregation logic to use the new futures - Add comments to explain the cache stampede prevention mechanism
fulleni
deleted the
Refactor-Country-Service-for-Concurrency-and-Type-Safety
branch
![gemini-code-assist[bot]](https://avatars.githubusercontent.com/in/956858?s=60&v=4){kind=small}
There was a problem hiding this comment.
Summary of Changes
Hello @fulleni, 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 addresses potential performance and concurrency issues within the CountryService by implementing a cache stampede prevention mechanism. It ensures that concurrent requests for cached country lists do not trigger multiple redundant database aggregations. Additionally, the changes enhance the type safety of a core helper method, making the codebase more robust and easier to maintain.
Highlights
- Cache Stampede Prevention: Introduced a mechanism to prevent cache stampedes by holding references to in-flight asynchronous operations. This ensures that if multiple concurrent requests for the same data arrive while a fetch is already in progress, subsequent requests will await the result of the ongoing operation instead of initiating new, redundant fetches.
- Improved Type Safety: Enhanced the
_getDistinctCountriesFromAggregationhelper method by introducing a generic type parameter. This improves the type safety of the method, ensuring that theDataRepositorypassed to it adheres to expected types, leading to more robust and maintainable code.
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 in your pull request via creating an issue comment (i.e. comment on the pull request page) using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands.
| 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 issue 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
-
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. ↩
There was a problem hiding this comment.
Code Review
This pull request aims to prevent cache stampedes in CountryService by caching in-flight requests. The approach is sound, but the current implementation has a race condition that could still lead to multiple concurrent database queries. My feedback includes a suggestion for a more robust, atomic pattern using Dart's null-aware assignment operator, which also helps reduce code duplication between the methods for fetching event and headquarter countries. The change to add generics for type safety is a good improvement.
Status
READY
Description
Addresses potential race conditions in CountryService by introducing in-flight request handling for cached country lists, preventing multiple concurrent database aggregations. It also enhances type safety in the _getDistinctCountriesFromAggregation helper method by using a generic type parameter.
Type of Change