| |
| |
| |
| |
| |
| |
| """The cache has to forget. Callers name the model, so the set of models a running instance is |
| asked for is open-ended; without a bound, every distinct id ever requested stays resident and the |
| container eventually dies. Least-recently-used is the right eviction order here because the working |
| set in practice is a couple of models used constantly plus a long tail used once. |
| """ |
|
|
| import logging |
|
|
| import pytest |
| from src.model_cache import LruCache |
|
|
|
|
| def _cache(max_entries: int = 2) -> LruCache: |
| return LruCache(max_entries=max_entries, name="test", logger=logging.getLogger("test")) |
|
|
|
|
| def test_stores_and_returns_values(): |
| cache = _cache() |
| cache["a"] = 1 |
|
|
| assert "a" in cache |
| assert cache["a"] == 1 |
|
|
|
|
| def test_reports_absent_keys(): |
| cache = _cache() |
|
|
| assert "missing" not in cache |
|
|
|
|
| def test_evicts_the_least_recently_used_entry_when_full(): |
| cache = _cache(max_entries=2) |
| cache["a"] = 1 |
| cache["b"] = 2 |
|
|
| cache["c"] = 3 |
|
|
| assert "a" not in cache, "the oldest entry should have been evicted" |
| assert "b" in cache |
| assert "c" in cache |
| assert len(cache) == 2 |
|
|
|
|
| def test_reading_an_entry_makes_it_recently_used(): |
| """Otherwise the model being hammered by every request would be the one evicted.""" |
| cache = _cache(max_entries=2) |
| cache["a"] = 1 |
| cache["b"] = 2 |
|
|
| _ = cache["a"] |
| cache["c"] = 3 |
|
|
| assert "a" in cache |
| assert "b" not in cache |
| assert "c" in cache |
|
|
|
|
| def test_overwriting_an_existing_key_does_not_evict(): |
| cache = _cache(max_entries=2) |
| cache["a"] = 1 |
| cache["b"] = 2 |
|
|
| cache["a"] = 99 |
|
|
| assert len(cache) == 2 |
| assert cache["a"] == 99 |
| assert "b" in cache |
|
|
|
|
| def test_capacity_is_at_least_one(): |
| """A zero or negative limit would evict the entry a request just loaded, before it could be |
| used, and turn every single request into a fresh load.""" |
| cache = _cache(max_entries=0) |
| cache["a"] = 1 |
|
|
| assert cache["a"] == 1 |
| assert len(cache) == 1 |
|
|
|
|
| def test_eviction_is_logged(caplog): |
| """Thrashing is invisible otherwise — the symptom is only slowness.""" |
| cache = _cache(max_entries=1) |
| with caplog.at_level(logging.INFO): |
| cache["a"] = 1 |
| cache["b"] = 2 |
|
|
| assert any("a" in record.message for record in caplog.records) |
|
|
|
|
| def test_evicted_entries_are_gone_not_merely_hidden(): |
| """The point is to release the reference so the weights can be garbage collected.""" |
| cache = _cache(max_entries=1) |
| cache["a"] = object() |
| cache["b"] = object() |
|
|
| with pytest.raises(KeyError): |
| _ = cache["a"] |
|
|
