fix(firestore): Further improved performance of UTF-8 string comparison logic #7098
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Summary of Changes
Hello @dconeybe, 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 delivers a critical performance enhancement for Firestore's UTF-8 string ordering logic, which had previously regressed and caused customer-reported issues. It introduces a new, highly optimized comparison utility that avoids memory allocations, ensuring faster and more efficient string operations. This change also refactors the codebase by centralizing the comparison logic and updating existing components to leverage the new, improved implementation, alongside adding robust test coverage.
Highlights
- Performance Improvement: Implemented a highly optimized, allocation-free UTF-8 string comparison logic to address significant performance degradation in Firestore's string ordering, specifically fixing issue #7053.
- Code Refactoring: Extracted the UTF-8 string comparison logic into a new dedicated
Utf8Compareutility class, centralizing the functionality and removing the less efficient, previous implementation fromUtil.java. - Test Coverage: Introduced a new comprehensive test suite for the
Utf8Compareclass, including extensive random string generation to validate correctness across various Unicode characters and surrogate pairs.
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Code Review
The pull request introduces a new Utf8Compare class to improve the performance of UTF-8 string comparisons. The changes involve replacing calls to Util.compareUtf8Strings with Utf8Compare.compareUtf8Strings in BasePath and Values classes. Additionally, a new test class Utf8CompareTest is added to verify the correctness of the new comparison logic. The old implementation of compareUtf8Strings is removed from Util class. The debug checks in Utf8Compare class could be improved by logging errors instead of throwing exceptions.
firebase-firestore/src/main/java/com/google/firebase/firestore/util/Utf8Compare.java
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firebase-firestore/src/main/java/com/google/firebase/firestore/util/Utf8Compare.java
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Coverage Report 1Affected Products
Test Logs |
Test Results 186 files - 797 186 suites - 797 4m 42s ⏱️ - 29m 1s Results for commit 02c2371. ± Comparison against base commit ec904ec. This pull request removes 4317 tests.♻️ This comment has been updated with latest results. |
Size Report 1Affected Products
Test Logs |
Startup Time Report 1Note: Layout is sometimes suboptimal due to limited formatting support on GitHub. Please check this report on GCS. Notes
Startup Times
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Pull Request Overview
This PR replaces the previous UTF-8 byte-oriented string comparison with a more efficient surrogate-aware char-by-char algorithm and updates the changelog to document the fix.
- Simplified
compareUtf8Stringsto a single-pass char comparison usingCharacter.isSurrogate - Removed
ByteStringfallback and eliminated codePoint/substring overhead - Added an unreleased entry in
CHANGELOG.mdfor the performance fix
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| firebase-firestore/src/main/java/com/google/firebase/firestore/util/Util.java | Rewrote compareUtf8Strings with optimized surrogate-aware logic; removed helper and ByteString paths |
| firebase-firestore/CHANGELOG.md | Documented the UTF-8 comparison performance improvement under Unreleased |
Comments suppressed due to low confidence (2)
firebase-firestore/src/main/java/com/google/firebase/firestore/util/Util.java:90
- Update this Javadoc to describe the new surrogate-aware, char-by-char comparison algorithm rather than the previous byte-level UTF-8 logic.
/** Compare strings in UTF-8 encoded byte order */
firebase-firestore/src/main/java/com/google/firebase/firestore/util/Util.java:113
- Add unit tests covering edge cases around surrogate pairs versus non-surrogate characters to verify the new comparison logic across diverse Unicode inputs.
for (int i = 0; i < length; i++) {
firebase-firestore/src/main/java/com/google/firebase/firestore/util/Util.java
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firebase-firestore/src/main/java/com/google/firebase/firestore/util/Util.java
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Further improved performance of UTF-8 string ordering logic, which had degraded in v25.1.2 due to the fix #6615 and received some improvements in v25.1.3 by the fix #6706. Even with these improvements, customers still observed a material performance degradation (#7053), which this PR addresses.
This PR was ported to the web sdk in firebase/firebase-js-sdk#9143
Fixes: #7053