diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index 7ad2198d96..6ec8a6345d 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -18,6 +18,7 @@ from twisted.internet import defer
from collections import namedtuple
from ._base import SQLBaseStore
+from synapse.util.caches import intern_string
from synapse.util.caches.descriptors import cached, cachedInlineCallbacks
from synapse.util.stringutils import to_ascii
@@ -482,6 +483,44 @@ class RoomMemberStore(SQLBaseStore):
defer.returnValue(False)
+ def get_joined_hosts(self, room_id, state_group, state_ids):
+ if not state_group:
+ # If state_group is None it means it has yet to be assigned a
+ # state group, i.e. we need to make sure that calls with a state_group
+ # of None don't hit previous cached calls with a None state_group.
+ # To do this we set the state_group to a new object as object() != object()
+ state_group = object()
+
+ return self._get_joined_hosts(
+ room_id, state_group, state_ids
+ )
+
+ @cachedInlineCallbacks(num_args=2, max_entries=10000, iterable=True)
+ def _get_joined_hosts(self, room_id, state_group, current_state_ids):
+ # We don't use `state_group`, its there so that we can cache based
+ # on it. However, its important that its never None, since two current_state's
+ # with a state_group of None are likely to be different.
+ # See bulk_get_push_rules_for_room for how we work around this.
+ assert state_group is not None
+
+ joined_hosts = set()
+ for (etype, state_key), event_id in current_state_ids.items():
+ if etype == EventTypes.Member:
+ try:
+ host = get_domain_from_id(state_key)
+ except:
+ logger.warn("state_key not user_id: %s", state_key)
+ continue
+
+ if host in joined_hosts:
+ continue
+
+ event = yield self.get_event(event_id, allow_none=True)
+ if event and event.content["membership"] == Membership.JOIN:
+ joined_hosts.add(intern_string(host))
+
+ defer.returnValue(joined_hosts)
+
@defer.inlineCallbacks
def _background_add_membership_profile(self, progress, batch_size):
target_min_stream_id = progress.get(
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