Documentation

docs/tcp_replication.rst

@@ -137,7 +137,6 @@ for each stream so that on reconneciton it can start streaming from the correct
 place. Note: not all RDATA have valid tokens due to batching. See
 ``RdataCommand`` for more details.
 
-
 Example
 ~~~~~~~
 
@@ -221,3 +220,23 @@ SYNC (S, C)
 
 See ``synapse/replication/tcp/commands.py`` for a detailed description and the
 format of each command.
+
+
+Cache Invalidation Stream
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The cache invalidation stream is used to inform workers when they need to
+invalidate any of their caches in the data store. This is done by streaming all
+cache invalidations done on master down to the workers, assuming that any caches
+on the workers also exist on the master.
+
+Each individual cache invalidation results in a row being sent down replication,
+which includes the cache name (the name of the function) and they key to
+invalidate. For example::
+
+    > RDATA caches 550953771 ["get_user_by_id", ["@bob:example.com"], 1550574873251]
+
+However, there are times when a number of caches need to be invalidated at the
+same time with the same key. To reduce traffic we batch those invalidations into
+a single poke by defining a special cache name that workers understand to mean
+to expand to invalidate the correct caches.

synapse/storage/_base.py

@@ -1199,8 +1199,8 @@ def _invalidate_state_caches_and_stream(self, txn, room_id, members_changed):
 
         Args:
             txn
-            room_id (str): Room were state changed
-            members_changed (set[str]): The user_ids of members that have changed
+            room_id (str): Room where state changed
+            members_changed (Iterable[str]): The user_ids of members that have changed
         """
         txn.call_after(self._invalidate_state_caches, room_id, members_changed)
 
@@ -1215,7 +1215,7 @@ def _invalidate_state_caches(self, room_id, members_changed):
         not stream invalidations down replication.
 
         Args:
-            room_id (str): Room were state changed
+            room_id (str): Room where state changed
             members_changed (set[str]): The user_ids of members that have changed
         """
         for member in members_changed:
@@ -1237,7 +1237,7 @@ def _send_invalidation_to_replication(self, txn, cache_name, keys):
         Args:
             txn
             cache_name (str)
-            keys (list[str])
+            keys (iterable[str])
         """
 
         if isinstance(self.database_engine, PostgresEngine):