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Python: Fix Purview cache size accounting when replacing entries #8990

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Python: Fix Purview cache size accounting when replacing entries #8990

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11225ab
fix(purview): remove replaced cache entries before eviction
dhairyajangir Oct 2, 2026
db8cc2e
test(purview): cover replacement eviction at cache capacity
dhairyajangir Oct 2, 2026
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8 changes: 4 additions & 4 deletions python/packages/purview/agent_framework_purview/_cache.py
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Original file line number Diff line number Diff line change
Expand Up @@ -139,10 +139,10 @@ async def set(self, key: str, value: Any, ttl_seconds: int | None = None) -> Non
expiry = time.time() + ttl
size = self._estimate_size(value)

# Remove old entry if exists
if key in self._cache:
old_size = self._cache[key][2]
self._current_size_bytes -= old_size
# Remove the old entry so eviction cannot count its size again.
old_entry = self._cache.pop(key, None)
if old_entry is not None:
self._current_size_bytes -= old_entry[2]

# Evict if needed
self._evict_if_needed(size)
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19 changes: 19 additions & 0 deletions python/packages/purview/tests/purview/test_cache.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,8 @@

import asyncio

import pytest

from agent_framework_purview._cache import (
InMemoryCacheProvider,
create_protection_scopes_cache_key,
Expand Down Expand Up @@ -65,6 +67,23 @@ async def test_cache_update_existing_key(self) -> None:

assert result == "value2"

async def test_cache_growing_update_evicts_other_entries(self, monkeypatch: pytest.MonkeyPatch) -> None:
"""Replacing the earliest-expiring entry must only subtract its size once."""
monkeypatch.setattr("agent_framework_purview._cache.time.time", lambda: 1000.0)
cache = InMemoryCacheProvider(max_size_bytes=20)

# JSON string quotes add two bytes to each value's estimated size.
await cache.set("older", "a" * 6, ttl_seconds=10)
await cache.set("newer", "b" * 6, ttl_seconds=20)
await cache.set("older", "c" * 14, ttl_seconds=30)

assert await cache.get("older") == "c" * 14
assert await cache.get("newer") is None
assert cache._current_size_bytes == 16

await cache.remove("older")
assert cache._current_size_bytes == 0

async def test_cache_remove(self) -> None:
"""Test removing a cache entry."""
cache = InMemoryCacheProvider()
Expand Down
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