add a cache to have_seen_event (#9953)

Empirically, this helped my server considerably when handling gaps in Matrix HQ. The problem was that we would repeatedly call have_seen_events for the same set of (50K or so) auth_events, each of which would take many minutes to complete, even though it's only an index scan.

2 files changed, 109 insertions, 0 deletions

diff --git a/tests/storage/databases/main/__init__.py b/tests/storage/databases/main/__init__.py
new file mode 100644
index 0000000000..c24c7ecd92
--- /dev/null
+++ b/tests/storage/databases/main/__init__.py
@@ -0,0 +1,13 @@
+# Copyright 2021 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
diff --git a/tests/storage/databases/main/test_events_worker.py b/tests/storage/databases/main/test_events_worker.py
new file mode 100644
index 0000000000..932970fd9a
--- /dev/null
+++ b/tests/storage/databases/main/test_events_worker.py
@@ -0,0 +1,96 @@
+# Copyright 2021 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import json
+
+from synapse.logging.context import LoggingContext
+from synapse.storage.databases.main.events_worker import EventsWorkerStore
+
+from tests import unittest
+
+
+class HaveSeenEventsTestCase(unittest.HomeserverTestCase):
+    def prepare(self, reactor, clock, hs):
+        self.store: EventsWorkerStore = hs.get_datastore()
+
+        # insert some test data
+        for rid in ("room1", "room2"):
+            self.get_success(
+                self.store.db_pool.simple_insert(
+                    "rooms",
+                    {"room_id": rid, "room_version": 4},
+                )
+            )
+
+        for idx, (rid, eid) in enumerate(
+            (
+                ("room1", "event10"),
+                ("room1", "event11"),
+                ("room1", "event12"),
+                ("room2", "event20"),
+            )
+        ):
+            self.get_success(
+                self.store.db_pool.simple_insert(
+                    "events",
+                    {
+                        "event_id": eid,
+                        "room_id": rid,
+                        "topological_ordering": idx,
+                        "stream_ordering": idx,
+                        "type": "test",
+                        "processed": True,
+                        "outlier": False,
+                    },
+                )
+            )
+            self.get_success(
+                self.store.db_pool.simple_insert(
+                    "event_json",
+                    {
+                        "event_id": eid,
+                        "room_id": rid,
+                        "json": json.dumps({"type": "test", "room_id": rid}),
+                        "internal_metadata": "{}",
+                        "format_version": 3,
+                    },
+                )
+            )
+
+    def test_simple(self):
+        with LoggingContext(name="test") as ctx:
+            res = self.get_success(
+                self.store.have_seen_events("room1", ["event10", "event19"])
+            )
+            self.assertEquals(res, {"event10"})
+
+            # that should result in a single db query
+            self.assertEquals(ctx.get_resource_usage().db_txn_count, 1)
+
+        # a second lookup of the same events should cause no queries
+        with LoggingContext(name="test") as ctx:
+            res = self.get_success(
+                self.store.have_seen_events("room1", ["event10", "event19"])
+            )
+            self.assertEquals(res, {"event10"})
+            self.assertEquals(ctx.get_resource_usage().db_txn_count, 0)
+
+    def test_query_via_event_cache(self):
+        # fetch an event into the event cache
+        self.get_success(self.store.get_event("event10"))
+
+        # looking it up should now cause no db hits
+        with LoggingContext(name="test") as ctx:
+            res = self.get_success(self.store.have_seen_events("room1", ["event10"]))
+            self.assertEquals(res, {"event10"})
+            self.assertEquals(ctx.get_resource_usage().db_txn_count, 0)