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| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
Abhay Singh
|
cf6367add4
|
fix(cache/semantic): don't evict an unrelated entry on an update at capacity (#2094)
## Description
`SemanticCache.put` can evict a perfectly good, unrelated entry when it
merely updates a key that is already cached.
The method runs its at-capacity eviction loop *before* it computes the
entry's key:
```python
self._cleanup_expired()
# Evict if at capacity
while len(self._cache) >= self.config.max_entries:
self._evict_oldest()
...
key = messages_hash or self._generate_key(query)
...
self._cache[key] = entry
```
So when the same key is stored again while the cache is full (a
duplicate store, or a retried request that produces the same
`messages_hash`), the loop fires because `len == max_entries`, evicts
the LRU-oldest *distinct* entry, and only then overwrites the existing
key in place. Writing to an already-present key does not grow the map,
so nothing needed to be evicted — but an unrelated live entry is now
gone, and the next `get` for it is a false miss.
Concretely, with `max_entries=2` and keys `[h1, h2]`, re-storing `h2`
evicts `h1`, leaving `[h2]` even though only two distinct keys were ever
stored.
The sibling `CompressionCache.store_compressed` gets this right: it
deletes the existing key first, inserts, and only then trims — so
re-storing a present key never drops an unrelated entry.
## Fix
Compute the key first, then run the eviction loop only while the key is
genuinely new:
```python
key = messages_hash or self._generate_key(query)
while key not in self._cache and len(self._cache) >= self.config.max_entries:
self._evict_oldest()
```
An in-place update of an existing key no longer evicts anything; adding
a new key still trims to make room exactly as before.
Closes #
## Type of Change
- [x] Bug fix (non-breaking change that fixes an issue)
- [ ] New feature (non-breaking change that adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update
- [ ] Performance improvement
- [ ] Code refactoring (no functional changes)
## Changes Made
- `headroom/cache/semantic.py`: move the cache-key computation above the
eviction loop and gate the loop on `key not in self._cache` so an
in-place update never evicts.
- `tests/test_cache/test_semantic.py`: add
`test_update_at_capacity_does_not_evict_unrelated_entry`.
- `CHANGELOG.md`: Bug Fixes entry.
## Testing
- [ ] Unit tests pass (`pytest`)
- [x] Linting passes (`ruff check .`)
- [ ] Type checking passes (`mypy headroom`)
- [x] New tests added for new functionality
- [ ] Manual testing performed
### Test Output
```text
$ uvx ruff@0.15.17 check headroom/cache/semantic.py tests/test_cache/test_semantic.py
All checks passed!
$ python -m py_compile headroom/cache/semantic.py tests/test_cache/test_semantic.py
OK
```
## Real Behavior Proof
- Environment: Windows 11, Python 3.12, `uvx ruff@0.15.17`. Importing
`headroom` pulls in the torch/transformers stack and a full `pytest`
gets OOM-killed on this box, so I verified the eviction logic with a
dependency-free script that replicates the `OrderedDict` +
`_evict_oldest` (popitem last=False) behavior for the old vs new loop,
and left the full pytest to CI.
- Exact command / steps: with `max_entries=2`, store `h1` then `h2`,
then re-store the already-present `h2`, under both the old loop (evict
before key dedup) and the new loop (evict only when key is new).
- Observed result: old loop leaves `['h2']` and `get(h1)` returns `None`
(h1 wrongly evicted); new loop leaves `['h1', 'h2']` with `get(h1)`
intact and `h2` updated. The regression test asserts h1 survives and h2
reflects the update.
- Not tested: a live embedding-backed cache round-trip; full local
`pytest` deferred to CI (OOM, per above).
## Review Readiness
- [x] I have performed a self-review
- [x] This PR is ready for human review
## Checklist
- [x] My code follows the project's style guidelines
- [x] I have performed a self-review of my code
- [x] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [x] I have updated the CHANGELOG.md if applicable
## Additional Notes
The "unit tests pass locally" and "type checking" boxes are unchecked
because the full suite imports the ML stack, which I can't run in this
environment; the change is a localized reordering of two existing
statements plus a loop guard, verified by the standalone proof and the
new regression test for CI. This is a different defect from the earlier
messages-hash keying fix — that one was about which slot a request maps
to; this one is about eviction dropping a live entry on an in-place
update.
Co-authored-by: Tejas Chopra <chopratejas@gmail.com>
|
||
|
Abhay Singh
|
d8783ab89b
|
fix(cache/semantic): key entries by context hash, not query text (#2022)
## Description
`SemanticCache` (`headroom/cache/semantic.py`) derives each entry's key
from the **query text
only** — where `query` is just the trailing user message — and its
exact-match lookup returns
the slot without checking the stored entry's `messages_hash`:
```python
# put()
key = self._generate_key(query) # sha256(query)[:16]
self._cache[key] = entry
if messages_hash:
self._hash_index[messages_hash] = key
# get() — exact-match branch
key = self._hash_index.get(messages_hash)
if key and key in self._cache:
entry = self._cache[key]
...
return entry # never checks entry.messages_hash
```
So two requests that share a trailing user message but differ in earlier
context map to the
**same** key. The second `put` overwrites the first, and the first
request's `messages_hash`
still points at that (now overwritten) slot — so it is served the
**other conversation's**
cached response.
Trailing messages like `"continue"`, `"yes"`, `"fix it"`, `"run the
tests"` are extremely
common in agentic/coding sessions, so this collides constantly. It's
independent of the
proxy-level `_compute_key` fix (that's about what goes *into*
`messages_hash`; here the entry
is stored under a query-only key regardless of how good the hash is).
This `SemanticCache` is
the one used by the SDK client's `enable_semantic_cache` path.
Concretely:
1. `put("run the tests", A, messages_hash=HA)` → key `K = sha256("run
the tests")`; `_cache[K]=A`.
2. `put("run the tests", B, messages_hash=HB)` → same `K`; `_cache[K]`
overwritten with `B`.
3. `get("run the tests", HA)` → `_hash_index[HA]=K`, `K in _cache` →
returns **B**.
Closes: no issue filed — found while auditing the cache key derivation.
## Fix
1. Key entries by the full-context `messages_hash` when present, falling
back to the query hash
only when no hash is supplied:
```python
key = messages_hash or self._generate_key(query)
```
2. Defensively verify `entry.messages_hash == messages_hash` in the
exact-match branch of `get`,
so any residual stale mapping becomes a miss rather than wrong data.
## Type of Change
- [x] Bug fix (non-breaking change that fixes an issue)
## Changes Made
- `headroom/cache/semantic.py`: key `put` entries by `messages_hash`
when present; verify `entry.messages_hash` in the `get` exact-match
branch.
- `tests/test_cache/test_semantic.py`: add
`test_same_query_different_context_does_not_collide` and
`test_exact_match_verifies_messages_hash`.
## Testing
- [x] New regression tests added (`tests/test_cache/test_semantic.py`)
- [x] Linting/formatting clean — run with the CI-pinned `ruff==0.15.17`
- [ ] Full `pytest` deferred to CI (local-OOM reason below).
```text
$ uvx ruff@0.15.17 check headroom/cache/semantic.py tests/test_cache/test_semantic.py
All checks passed!
```
## Real Behavior Proof
- Environment: Windows 11, Python 3.10, headroom from this branch.
Importing `headroom` pulls in the torch/transformers stack and a full
`pytest` gets OOM-killed on this box, so I verified the `put`/`get`
logic with a dependency-free script and left the full pytest to CI.
- Exact command / steps: stored responses A and B under the same query
`"run the tests"` with different `messages_hash`, then read each hash
back — through both the old (query-keyed) and new (hash-keyed) logic.
- Observed result: the old logic serves B's response to request A; the
new logic isolates them:
```text
OLD: A->RESPONSE_B B->RESPONSE_B
NEW: A->RESPONSE_A B->RESPONSE_B
SEMANTIC CACHE COLLISION FIX VERIFIED (OLD served B to A; NEW isolates)
```
- Not tested: the full SDK `HeadroomClient` round-trip with
`enable_semantic_cache=True` (needs the heavy stack). The fix is
confined to `SemanticCache.put`/`get` and the new tests drive them
directly. Full local `pytest` deferred to CI (OOM, per above).
## Review Readiness
- [x] I have performed a self-review
- [x] This PR is ready for human review
## Checklist
- [x] My code follows the project's style guidelines
- [x] I have performed a self-review of my code
- [x] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes — ran
lint + a standalone logic check; full pytest deferred to CI (local OOM,
disclosed above)
- [x] I have updated the CHANGELOG.md if applicable
## Additional Notes
- Small, contained fix — the key derivation plus a verification guard,
no new dependencies.
- @JerrettDavis tagging you — this one can serve one conversation's
cached response to another when the last message matches, so it seemed
worth surfacing. Thanks!
|
||
|
chopratejas
|
e4a41faa33 |
Fix all ruff lint and format errors for CI
- Fix E402: Move module-level imports to top of file - Fix F401: Add noqa for availability check imports - Fix F402: Rename loop variables shadowing imports - Fix E722: Replace bare except with except Exception - Fix B904: Add exception chaining (from e) - Fix F811: Remove duplicate imports - Fix B027: Add noqa for empty close() method - Fix E741: Rename ambiguous variable l -> label - Fix I001: Import sorting issues - Apply ruff format to all 106 files All 902 tests pass. |
||
|
chopratejas
|
7a05808e0f |
Add cache optimization module with scalable dynamic content detection
Implements a comprehensive cache optimization layer for LLM providers: - Provider-specific optimizers (Anthropic, OpenAI, Google) with distinct caching strategies: explicit breakpoints, prefix stabilization, and CachedContent API respectively - Scalable dynamic content detector using three strategies: 1. Structural detection: "Label: value" patterns (language-agnostic) 2. Entropy-based detection: high-entropy strings (IDs, tokens, hashes) 3. Universal patterns: ISO 8601, UUIDs, JWTs, hex hashes - NO hardcoded locale-specific patterns (no month names, etc.) - Semantic caching layer with LRU eviction and TTL support - Plugin registry for provider selection and custom optimizers - 131 tests, real-world benchmarks showing 20-55% compression at <0.3ms |