Prefill the device_list_stream_cache (#12367)

* Prefill the device_list_stream_cache

* Newsfile

* Newsfile

3 files changed, 23 insertions, 2 deletions

diff --git a/changelog.d/12367.feature b/changelog.d/12367.feature
new file mode 100644

index 0000000000..34bb60e966
--- /dev/null
+++ b/changelog.d/12367.feature
@@ -0,0 +1 @@
+Reduce overhead of restarting synchrotrons.
diff --git a/synapse/replication/slave/storage/devices.py b/synapse/replication/slave/storage/devices.py

index f040e33bfb..00a634d3a9 100644
--- a/synapse/replication/slave/storage/devices.py
+++ b/synapse/replication/slave/storage/devices.py
@@ -48,8 +48,18 @@ class SlavedDeviceStore(EndToEndKeyWorkerStore, DeviceWorkerStore, BaseSlavedSto
             ],
         )
         device_list_max = self._device_list_id_gen.get_current_token()
+        device_list_prefill, min_device_list_id = self.db_pool.get_cache_dict(
+            db_conn,
+            "device_lists_stream",
+            entity_column="user_id",
+            stream_column="stream_id",
+            max_value=device_list_max,
+            limit=1000,
+        )
         self._device_list_stream_cache = StreamChangeCache(
-            "DeviceListStreamChangeCache", device_list_max
+            "DeviceListStreamChangeCache",
+            min_device_list_id,
+            prefilled_cache=device_list_prefill,
         )
         self._user_signature_stream_cache = StreamChangeCache(
             "UserSignatureStreamChangeCache", device_list_max
diff --git a/synapse/storage/databases/main/__init__.py b/synapse/storage/databases/main/__init__.py

index cdbe3872fa..d4a38daa9a 100644
--- a/synapse/storage/databases/main/__init__.py
+++ b/synapse/storage/databases/main/__init__.py
@@ -184,8 +184,18 @@ class DataStore(
         super().__init__(database, db_conn, hs)
 
         device_list_max = self._device_list_id_gen.get_current_token()
+        device_list_prefill, min_device_list_id = self.db_pool.get_cache_dict(
+            db_conn,
+            "device_lists_stream",
+            entity_column="user_id",
+            stream_column="stream_id",
+            max_value=device_list_max,
+            limit=1000,
+        )
         self._device_list_stream_cache = StreamChangeCache(
-            "DeviceListStreamChangeCache", device_list_max
+            "DeviceListStreamChangeCache",
+            min_device_list_id,
+            prefilled_cache=device_list_prefill,
         )
         self._user_signature_stream_cache = StreamChangeCache(
             "UserSignatureStreamChangeCache", device_list_max