From 1b4d5d6acf8cfbe65601b881360ea730f9693d80 Mon Sep 17 00:00:00 2001 From: Patrick Cloke Date: Wed, 6 Jan 2021 12:33:20 -0500 Subject: [PATCH] Empty iterables should count towards cache usage. (#9028) --- changelog.d/9028.bugfix | 1 + synapse/util/caches/deferred_cache.py | 2 +- tests/util/caches/test_deferred_cache.py | 75 ++++++++++++++++-------- 3 files changed, 53 insertions(+), 25 deletions(-) create mode 100644 changelog.d/9028.bugfix diff --git a/changelog.d/9028.bugfix b/changelog.d/9028.bugfix new file mode 100644 index 0000000000..66666886a4 --- /dev/null +++ b/changelog.d/9028.bugfix @@ -0,0 +1 @@ +Fix a long-standing bug where some caches could grow larger than configured. diff --git a/synapse/util/caches/deferred_cache.py b/synapse/util/caches/deferred_cache.py index 601305487c..1adc92eb90 100644 --- a/synapse/util/caches/deferred_cache.py +++ b/synapse/util/caches/deferred_cache.py @@ -105,7 +105,7 @@ class DeferredCache(Generic[KT, VT]): keylen=keylen, cache_name=name, cache_type=cache_type, - size_callback=(lambda d: len(d)) if iterable else None, + size_callback=(lambda d: len(d) or 1) if iterable else None, metrics_collection_callback=metrics_cb, apply_cache_factor_from_config=apply_cache_factor_from_config, ) # type: LruCache[KT, VT] diff --git a/tests/util/caches/test_deferred_cache.py b/tests/util/caches/test_deferred_cache.py index dadfabd46d..ecd9efc4df 100644 --- a/tests/util/caches/test_deferred_cache.py +++ b/tests/util/caches/test_deferred_cache.py @@ -25,13 +25,8 @@ from tests.unittest import TestCase class DeferredCacheTestCase(TestCase): def test_empty(self): cache = DeferredCache("test") - failed = False - try: + with self.assertRaises(KeyError): cache.get("foo") - except KeyError: - failed = True - - self.assertTrue(failed) def test_hit(self): cache = DeferredCache("test") @@ -155,13 +150,8 @@ class DeferredCacheTestCase(TestCase): cache.prefill(("foo",), 123) cache.invalidate(("foo",)) - failed = False - try: + with self.assertRaises(KeyError): cache.get(("foo",)) - except KeyError: - failed = True - - self.assertTrue(failed) def test_invalidate_all(self): cache = DeferredCache("testcache") @@ -215,13 +205,8 @@ class DeferredCacheTestCase(TestCase): cache.prefill(2, "two") cache.prefill(3, "three") # 1 will be evicted - failed = False - try: + with self.assertRaises(KeyError): cache.get(1) - except KeyError: - failed = True - - self.assertTrue(failed) cache.get(2) cache.get(3) @@ -239,13 +224,55 @@ class DeferredCacheTestCase(TestCase): cache.prefill(3, "three") - failed = False - try: + with self.assertRaises(KeyError): cache.get(2) - except KeyError: - failed = True - - self.assertTrue(failed) cache.get(1) cache.get(3) + + def test_eviction_iterable(self): + cache = DeferredCache( + "test", max_entries=3, apply_cache_factor_from_config=False, iterable=True, + ) + + cache.prefill(1, ["one", "two"]) + cache.prefill(2, ["three"]) + + # Now access 1 again, thus causing 2 to be least-recently used + cache.get(1) + + # Now add an item to the cache, which evicts 2. + cache.prefill(3, ["four"]) + with self.assertRaises(KeyError): + cache.get(2) + + # Ensure 1 & 3 are in the cache. + cache.get(1) + cache.get(3) + + # Now access 1 again, thus causing 3 to be least-recently used + cache.get(1) + + # Now add an item with multiple elements to the cache + cache.prefill(4, ["five", "six"]) + + # Both 1 and 3 are evicted since there's too many elements. + with self.assertRaises(KeyError): + cache.get(1) + with self.assertRaises(KeyError): + cache.get(3) + + # Now add another item to fill the cache again. + cache.prefill(5, ["seven"]) + + # Now access 4, thus causing 5 to be least-recently used + cache.get(4) + + # Add an empty item. + cache.prefill(6, []) + + # 5 gets evicted and replaced since an empty element counts as an item. + with self.assertRaises(KeyError): + cache.get(5) + cache.get(4) + cache.get(6)