Add concept of StatelessContext

changelog.d/3550.misc

@@ -0,0 +1 @@
+Lazily load state on master process when using workers to reduce DB consumption

synapse/events/snapshot.py

@@ -13,56 +13,54 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import abc
+
 from frozendict import frozendict
 
 from twisted.internet import defer
 
 
-class EventContext(object):
+class StatelessContext(object):
     """
     Attributes:
-        current_state_ids (dict[(str, str), str]):
-            The current state map including the current event.
-            (type, state_key) -> event_id
-
-        prev_state_ids (dict[(str, str), str]):
-            The current state map excluding the current event.
-            (type, state_key) -> event_id
-
         state_group (int|None): state group id, if the state has been stored
             as a state group. This is usually only None if e.g. the event is
             an outlier.
         rejected (bool|str): A rejection reason if the event was rejected, else
             False
 
-        push_actions (list[(str, list[object])]): list of (user_id, actions)
-            tuples
-
         prev_group (int): Previously persisted state group. ``None`` for an
             outlier.
         delta_ids (dict[(str, str), str]): Delta from ``prev_group``.
             (type, state_key) -> event_id. ``None`` for an outlier.
 
         prev_state_events (?): XXX: is this ever set to anything other than
             the empty list?
+
+        current_state_ids (dict[(str, str), str]|None):
+            The current state map including the current event.
+            (type, state_key) -> event_id
+
+        prev_state_ids (dict[(str, str), str]|None):
+            The current state map excluding the current event.
+            (type, state_key) -> event_id
     """
 
+    __metaclass__ = abc.ABCMeta
+
     __slots__ = [
-        "current_state_ids",
-        "prev_state_ids",
         "state_group",
         "rejected",
         "prev_group",
         "delta_ids",
         "prev_state_events",
         "app_service",
+
+        "current_state_ids",
+        "prev_state_ids",
     ]
 
     def __init__(self):
-        # The current state including the current event
-        self.current_state_ids = None
-        # The current state excluding the current event
-        self.prev_state_ids = None
         self.state_group = None
 
         self.rejected = False
@@ -76,9 +74,39 @@ def __init__(self):
 
         self.app_service = None
 
+        # The current state including the current event
+        self.current_state_ids = None
+        # The current state excluding the current event
+        self.prev_state_ids = None
+
+    @abc.abstractmethod
+    def get_current_state_ids(self, store):
+        """Gets the current state IDs
+
+        Returns:
+            Deferred[dict[(str, str), str]|None]
+        """
+        raise NotImplementedError()
+
+    @abc.abstractmethod
+    def get_prev_state_ids(self, store):
+        """Gets the prev state IDs
+
+        Returns:
+            Deferred[dict[(str, str), str]|None]
+        """
+        raise NotImplementedError()
+
+
+class EventContext(StatelessContext):
+    """This is the same as StatelessContext, except guarantees that
+    current_state_ids and prev_state_ids are set.
+    """
+    __slots__ = []
+
     def serialize(self, event):
         """Converts self to a type that can be serialized as JSON, and then
-        deserialized by `deserialize`
+        deserialized by `DeserializedContext.deserialize`
 
         Args:
             event (FrozenEvent): The event that this context relates to
@@ -108,20 +136,52 @@ def serialize(self, event):
             "app_service_id": self.app_service.id if self.app_service else None
         }
 
+    def get_current_state_ids(self, store):
+        """Implements StatelessContext"""
+        return defer.succeed(self.current_state_ids)
+
+    def get_prev_state_ids(self, store):
+        """Implements StatelessContext"""
+        return defer.succeed(self.prev_state_ids)
+
+
+class DeserializedContext(StatelessContext):
+    """A context that comes from a serialized version of a StatelessContext.
+
+    It does not necessarily have current_state_ids and prev_state_ids filled
+    out (unlike EventContext), but does cache the results of
+    `get_current_state_ids` and `get_prev_state_ids`.
+
+    Attributes:
+        _have_fetched_state (bool): Whether we attempted to fill out
+            current_state_ids
+        _prev_state_id (str|None): If set then the event associated with the
+            context overrode the _prev_state_id
+        _event_type (str): The type of the event the context is associated with
+        _event_state_key (str|None): The state_key of the event the context is
+            associated with
+    """
+
+    __slots__ = [
+        "_have_fetched_state",
+        "_prev_state_id",
+        "_event_type",
+        "_event_state_key",
+    ]
+
     @staticmethod
-    @defer.inlineCallbacks
     def deserialize(store, input):
         """Converts a dict that was produced by `serialize` back into a
-        EventContext.
+        StatelessContext.
 
         Args:
             store (DataStore): Used to convert AS ID to AS object
             input (dict): A dict produced by `serialize`
 
         Returns:
-            EventContext
+            StatelessContext
         """
-        context = EventContext()
+        context = DeserializedContext()
         context.state_group = input["state_group"]
         context.rejected = input["rejected"]
         context.prev_group = input["prev_group"]
@@ -130,24 +190,56 @@ def deserialize(store, input):
 
         # We use the state_group and prev_state_id stuff to pull the
         # current_state_ids out of the DB and construct prev_state_ids.
-        prev_state_id = input["prev_state_id"]
-        event_type = input["event_type"]
-        event_state_key = input["event_state_key"]
+        context._prev_state_id = input["prev_state_id"]
+        context._event_type = input["event_type"]
+        context._event_state_key = input["event_state_key"]
 
-        context.current_state_ids = yield store.get_state_ids_for_group(
-            context.state_group,
-        )
-        if prev_state_id and event_state_key:
-            context.prev_state_ids = dict(context.current_state_ids)
-            context.prev_state_ids[(event_type, event_state_key)] = prev_state_id
-        else:
-            context.prev_state_ids = context.current_state_ids
+        context._have_fetched_state = False
 
         app_service_id = input["app_service_id"]
         if app_service_id:
             context.app_service = store.get_app_service_by_id(app_service_id)
 
-        defer.returnValue(context)
+        return context
+
+    @defer.inlineCallbacks
+    def get_current_state_ids(self, store):
+        """Implements StatelessContext"""
+
+        if not self._have_fetched_state:
+            yield self._fill_out_state(store)
+
+        defer.returnValue(self.current_state_ids)
+
+    @defer.inlineCallbacks
+    def get_prev_state_ids(self, store):
+        """Implements StatelessContext"""
+
+        if not self._have_fetched_state:
+            yield self._fill_out_state(store)
+
+        defer.returnValue(self.current_state_ids)
+
+    @defer.inlineCallbacks
+    def _fill_out_state(self, store):
+        """Called to populate the current_state_ids and prev_state_ids
+        attributes by loading from the database.
+        """
+        self._have_fetched_state = True
+
+        if self.state_group is None:
+            return
+
+        self.current_state_ids = yield store.get_state_ids_for_group(
+            self.state_group,
+        )
+        if self._prev_state_id:
+            self.prev_state_ids = dict(self.current_state_ids)
+
+            key = (self._event_type, self._event_state_key)
+            self.prev_state_ids[key] = self._prev_state_id
+        else:
+            self.prev_state_ids = self.current_state_ids
 
 
 def _encode_state_dict(state_dict):

synapse/handlers/_base.py

@@ -106,14 +106,20 @@ def ratelimit(self, requester, update=True):
 
     @defer.inlineCallbacks
     def maybe_kick_guest_users(self, event, context=None):
+        """
+        Args:
+            event (FrozenEvent)
+            context (StatelessContext)
+        """
         # Technically this function invalidates current_state by changing it.
         # Hopefully this isn't that important to the caller.
         if event.type == EventTypes.GuestAccess:
             guest_access = event.content.get("guest_access", "forbidden")
             if guest_access != "can_join":
                 if context:
+                    current_state_ids = yield context.get_current_state_ids(self.store)
                     current_state = yield self.store.get_events(
-                        list(context.current_state_ids.values())
+                        list(current_state_ids.values())
                     )
                 else:
                     current_state = yield self.state_handler.get_current_state(

synapse/handlers/message.py

@@ -850,6 +850,13 @@ def persist_and_notify_client_event(
         calculated the push actions for the event, and checked auth.
 
         This should only be run on master.
+
+        Args:
+            requester (Requester)
+            event (FrozenEvent)
+            context (StatelessContext)
+            ratelimit(bool)
+            extra_users (list[UserID])
         """
         assert not self.config.worker_app
 
@@ -884,9 +891,11 @@ def is_inviter_member_event(e):
                         e.sender == event.sender
                     )
 
+                current_state_ids = yield context.get_current_state_ids(self.store)
+
                 state_to_include_ids = [
                     e_id
-                    for k, e_id in iteritems(context.current_state_ids)
+                    for k, e_id in current_state_ids.iteritems()
                     if k[0] in self.hs.config.room_invite_state_types
                     or k == (EventTypes.Member, event.sender)
                 ]
@@ -922,8 +931,9 @@ def is_inviter_member_event(e):
                     )
 
         if event.type == EventTypes.Redaction:
+            prev_state_ids = yield context.get_prev_state_ids(self.store)
             auth_events_ids = yield self.auth.compute_auth_events(
-                event, context.prev_state_ids, for_verification=True,
+                event, prev_state_ids, for_verification=True,
             )
             auth_events = yield self.store.get_events(auth_events_ids)
             auth_events = {
@@ -943,11 +953,13 @@ def is_inviter_member_event(e):
                         "You don't have permission to redact events"
                     )
 
-        if event.type == EventTypes.Create and context.prev_state_ids:
-            raise AuthError(
-                403,
-                "Changing the room create event is forbidden",
-            )
+        if event.type == EventTypes.Create:
+            prev_state_ids = yield context.get_prev_state_ids(self.store)
+            if prev_state_ids:
+                raise AuthError(
+                    403,
+                    "Changing the room create event is forbidden",
+                )
 
         (event_stream_id, max_stream_id) = yield self.store.persist_event(
             event, context=context

synapse/replication/http/send_event.py

@@ -24,7 +24,7 @@
     SynapseError,
 )
 from synapse.events import FrozenEvent
-from synapse.events.snapshot import EventContext
+from synapse.events.snapshot import DeserializedContext
 from synapse.http.servlet import RestServlet, parse_json_object_from_request
 from synapse.types import Requester, UserID
 from synapse.util.caches.response_cache import ResponseCache
@@ -136,7 +136,9 @@ def _handle_request(self, request):
             event = FrozenEvent(event_dict, internal_metadata, rejected_reason)
 
             requester = Requester.deserialize(self.store, content["requester"])
-            context = yield EventContext.deserialize(self.store, content["context"])
+            context = yield DeserializedContext.deserialize(
+                self.store, content["context"],
+            )
 
             ratelimit = content["ratelimit"]
             extra_users = [UserID.from_string(u) for u in content["extra_users"]]