Don't invalidate the entire event cache when we purge history (#16905)

We do this by adding support to the LRU cache for "extra indices" based
on the cached value. This allows us to efficiently map from room ID to
the cached events and only invalidate those.

1 files changed, 31 insertions, 0 deletions

diff --git a/tests/util/test_lrucache.py b/tests/util/test_lrucache.py
index dcc2b4be89..3f0d8139f8 100644
--- a/tests/util/test_lrucache.py
+++ b/tests/util/test_lrucache.py
@@ -383,3 +383,34 @@ class MemoryEvictionTestCase(unittest.HomeserverTestCase):
         # the items should still be in the cache
         self.assertEqual(cache.get("key1"), 1)
         self.assertEqual(cache.get("key2"), 2)
+
+
+class ExtraIndexLruCacheTestCase(unittest.HomeserverTestCase):
+    def test_invalidate_simple(self) -> None:
+        cache: LruCache[str, int] = LruCache(10, extra_index_cb=lambda k, v: str(v))
+        cache["key1"] = 1
+        cache["key2"] = 2
+
+        cache.invalidate_on_extra_index("key1")
+        self.assertEqual(cache.get("key1"), 1)
+        self.assertEqual(cache.get("key2"), 2)
+
+        cache.invalidate_on_extra_index("1")
+        self.assertEqual(cache.get("key1"), None)
+        self.assertEqual(cache.get("key2"), 2)
+
+    def test_invalidate_multi(self) -> None:
+        cache: LruCache[str, int] = LruCache(10, extra_index_cb=lambda k, v: str(v))
+        cache["key1"] = 1
+        cache["key2"] = 1
+        cache["key3"] = 2
+
+        cache.invalidate_on_extra_index("key1")
+        self.assertEqual(cache.get("key1"), 1)
+        self.assertEqual(cache.get("key2"), 1)
+        self.assertEqual(cache.get("key3"), 2)
+
+        cache.invalidate_on_extra_index("1")
+        self.assertEqual(cache.get("key1"), None)
+        self.assertEqual(cache.get("key2"), None)
+        self.assertEqual(cache.get("key3"), 2)