Merge pull request #1792 from matrix-org/erikj/limit_cache_prefill_device

Limit number of entries to prefill from cache

synapse/storage/__init__.py

@@ -189,7 +189,8 @@ class DataStore(RoomMemberStore, RoomStore,
             db_conn, "device_inbox",
             entity_column="user_id",
             stream_column="stream_id",
-            max_value=max_device_inbox_id
+            max_value=max_device_inbox_id,
+            limit=1000,
         )
         self._device_inbox_stream_cache = StreamChangeCache(
             "DeviceInboxStreamChangeCache", min_device_inbox_id,
@@ -202,6 +203,7 @@ class DataStore(RoomMemberStore, RoomStore,
             entity_column="destination",
             stream_column="stream_id",
             max_value=max_device_inbox_id,
+            limit=1000,
         )
         self._device_federation_outbox_stream_cache = StreamChangeCache(
             "DeviceFederationOutboxStreamChangeCache", min_device_outbox_id,

synapse/storage/_base.py

@@ -838,18 +838,19 @@ class SQLBaseStore(object):
         return txn.execute(sql, keyvalues.values())
 
     def _get_cache_dict(self, db_conn, table, entity_column, stream_column,
-                        max_value):
+                        max_value, limit=100000):
         # Fetch a mapping of room_id -> max stream position for "recent" rooms.
         # It doesn't really matter how many we get, the StreamChangeCache will
         # do the right thing to ensure it respects the max size of cache.
         sql = (
             "SELECT %(entity)s, MAX(%(stream)s) FROM %(table)s"
-            " WHERE %(stream)s > ? - 100000"
+            " WHERE %(stream)s > ? - %(limit)s"
             " GROUP BY %(entity)s"
         ) % {
             "table": table,
             "entity": entity_column,
             "stream": stream_column,
+            "limit": limit,
         }
 
         sql = self.database_engine.convert_param_style(sql)