fix(cache): prevent over-invalidation of similarly named prompt prefixes in PromptCache - #1829

Open

Xayar145 wants to merge 4 commits into

langfuse:main from

Xayar145:fix/prompt-cache-invalidate-exact-prefix

Open

fix(cache): prevent over-invalidation of similarly named prompt prefixes in PromptCache #1829
Xayar145 wants to merge 4 commits into
langfuse:main from
Xayar145:fix/prompt-cache-invalidate-exact-prefix

Conversation

@Xayar145

@Xayar145 Xayar145 commented Aug 22, 2026 •

edited by greptile-apps Bot

Loading

Copy link

Copy Markdown

Summary

Fixes cache invalidation in PromptCache.invalidate():

Checks for exact prompt name matches or keys prefixed with {prompt_name}- instead of bare substring prefix matching (key.startswith(prompt_name)).
Added unit test test_prompt_cache_invalidate_exact_prefix_match.

Motivation

Previously, PromptCache.invalidate("summary") would unintentionally evict other prompt keys sharing the same name prefix (for example "summary_detailed-version:1" or "summary_qa-label:production"). Checking exact key match or hyphen-delimited prefix ensures only the target prompt is evicted.

Changes

langfuse/_utils/prompt_cache.py: Refactored invalidate() to match key == prompt_name or key.startswith(f"{prompt_name}-").
tests/unit/test_prompt.py: Added test ensuring sibling prompts with similar prefixes are not accidentally evicted.

Tests

Added test_prompt_cache_invalidate_exact_prefix_match verifying selective invalidation.

Greptile Summary

The PR narrows prompt-cache invalidation to exact keys and hyphen-delimited prefixes and adds a regression test for similarly prefixed names. The delimiter remains ambiguous for valid prompt names containing hyphens.

Updates PromptCache.invalidate() to avoid bare prefix matching.
Adds coverage showing that invalidating summary preserves summary_detailed.
Does not cover or preserve a sibling such as summary-detailed.

Confidence Score: 4/5

The PR is safe to merge with a non-blocking cache-correctness improvement recommended for hyphen-prefixed sibling prompt names.

The change fixes underscore-style prefix collisions, but the shared hyphen delimiter still causes distinct names such as summary-detailed to be evicted when summary is invalidated.

Files Needing Attention: langfuse/_utils/prompt_cache.py, tests/unit/test_prompt.py

Prompt To Fix All With AI

### Issue 1
langfuse/_utils/prompt_cache.py:186
**Hyphen-delimited names still collide**
For cached prompts named `summary` and `summary-detailed`, invalidating `summary` also matches `summary-detailed-version:1`, unnecessarily evicting the distinct sibling and forcing another API fetch on its next access. The added underscore case does not cover this collision because prompt names accept hyphens and cache metadata uses the same delimiter.
---
For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "test(prompt): add unit test for exact pr..." | Re-trigger Greptile}

Greptile also left 1 inline comment on this PR.

Context used:

Knowledge Base — Utils and Support Types

Xayar145 added 2 commits

August 22, 2026 09:25

@Xayar145


 fix(cache): prevent over-invalidation of similarly named prompt prefi...

7aa921a

...xes in PromptCache

@Xayar145


 test(prompt): add unit test for exact prompt name matching during cac...

686e392

...he invalidation

claude[bot]

claude Bot reviewed

Aug 22, 2026

View reviewed changes

@claude claude Bot left a comment

Copy link

Copy Markdown

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

@CLAassistant

CLAassistant commented Aug 22, 2026

Copy link

Copy Markdown

CLA assistant check
Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

greptile-apps[bot]

greptile-apps Bot reviewed

Aug 22, 2026

View reviewed changes

langfuse/_utils/prompt_cache.py Outdated

with self._lock:

for key in list(self._cache):

if key.startswith(prompt_name):

if key == prompt_name or key.startswith(prefix):

@greptile-apps greptile-apps Bot Aug 22, 2026

Copy link

Copy Markdown

Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

P2 Hyphen-delimited names still collide

For cached prompts named summary and summary-detailed, invalidating summary also matches summary-detailed-version:1, unnecessarily evicting the distinct sibling and forcing another API fetch on its next access. The added underscore case does not cover this collision because prompt names accept hyphens and cache metadata uses the same delimiter.

Knowledge Base Used: Utils and Support Types

Prompt To Fix With AI

This is a comment left during a code review.
Path: langfuse/_utils/prompt_cache.py
Line: 186
Comment:
**Hyphen-delimited names still collide**
For cached prompts named `summary` and `summary-detailed`, invalidating `summary` also matches `summary-detailed-version:1`, unnecessarily evicting the distinct sibling and forcing another API fetch on its next access. The added underscore case does not cover this collision because prompt names accept hyphens and cache metadata uses the same delimiter.
**Knowledge Base Used:** [Utils and Support Types](https://app.greptile.com/personal-org-4986/-/custom-context/knowledge-base/langfuse/langfuse-python/-/docs/utils-support.md)
---
For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

Xayar145 added 2 commits

August 22, 2026 10:48

@Xayar145


 fix(cache): match exact version and label prefixes in PromptCache.inv...

7a2219d

...alidate

@Xayar145


 test(cache): assert hyphenated sibling prompts are preserved during i...

a23c9ea

...nvalidation

Labels

None yet

2 participants

@Xayar145 @CLAassistant

Navigation Menu

Uh oh!

fix(cache): prevent over-invalidation of similarly named prompt prefixes in PromptCache - #1829

fix(cache): prevent over-invalidation of similarly named prompt prefixes in PromptCache #1829
Xayar145 wants to merge 4 commits into
langfuse:main from
Xayar145:fix/prompt-cache-invalidate-exact-prefix

Conversation

@Xayar145 Xayar145 commented Aug 22, 2026 •

edited by greptile-apps Bot

Loading

Uh oh!

Summary

Motivation

Changes

Tests

Greptile Summary

Confidence Score: 4/5

Uh oh!

@claude claude Bot left a comment

Choose a reason for hiding this comment

Claude Code Review

Uh oh!

CLAassistant commented Aug 22, 2026

Uh oh!

@greptile-apps greptile-apps Bot Aug 22, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Uh oh!

Conversation

@Xayar145 Xayar145 commented Aug 22, 2026 • edited by greptile-apps Bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary

Motivation

Changes

Tests

Greptile Summary

Confidence Score: 4/5

Uh oh!

@claude claude Bot left a comment

Choose a reason for hiding this comment

Claude Code Review

Uh oh!

CLAassistant commented Aug 22, 2026

Uh oh!

@greptile-apps greptile-apps Bot Aug 22, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

@Xayar145 Xayar145 commented Aug 22, 2026 •

edited by greptile-apps Bot

Loading