diff --git a/synapse/storage/state.py b/synapse/storage/state.py
index 3f4cbd61c4..0f86311ed4 100644
--- a/synapse/storage/state.py
+++ b/synapse/storage/state.py
@@ -1041,6 +1041,86 @@ class StateGroupWorkerStore(EventsWorkerStore, SQLBaseStore):
return count
+ def _find_unreferenced_groups(self, txn, state_groups):
+ """Used when purging history to figure out which state groups can be
+ deleted and which need to be de-delta'ed (due to one of its prev groups
+ being scheduled for deletion).
+
+ Args:
+ txn
+ state_groups (set[int]): Set of state groups referenced by events
+ that are going to be deleted.
+
+ Returns:
+ tuple[set[int], set[int]]: The set of state groups that can be
+ deleted and the set of state groups that need to be de-delta'ed
+ """
+ # Graph of state group -> previous group
+ graph = {}
+
+ # Set of events that we have found to be referenced by events
+ referenced_groups = set()
+
+ # Set of state groups we've already seen
+ state_groups_seen = set(state_groups)
+
+ # Set of state groups to handle next.
+ next_to_search = set(state_groups)
+ while next_to_search:
+ # We bound size of groups we're looking up at once, to stop the
+ # SQL query getting too big
+ if len(next_to_search) < 100:
+ current_search = next_to_search
+ next_to_search = set()
+ else:
+ lst = list(next_to_search)
+ current_search = set(lst[:100])
+ next_to_search = set(lst[100:])
+
+ # Check if state groups are referenced
+ sql = """
+ SELECT state_group, count(*) FROM event_to_state_groups
+ LEFT JOIN events_to_purge AS ep USING (event_id)
+ WHERE state_group IN (%s) AND ep.event_id IS NULL
+ GROUP BY state_group
+ """ % (",".join("?" for _ in current_search),)
+ txn.execute(sql, list(current_search))
+
+ referenced = set(sg for sg, cnt in txn if cnt > 0)
+ referenced_groups |= referenced
+
+ # We don't continue iterating up the state group graphs for state
+ # groups that are referenced.
+ current_search -= referenced
+
+ rows = self._simple_select_many_txn(
+ txn,
+ table="state_group_edges",
+ column="prev_state_group",
+ iterable=current_search,
+ keyvalues={},
+ retcols=("prev_state_group", "state_group",),
+ )
+
+ next_to_search.update(row["state_group"] for row in rows)
+ # We don't bother re-handling groups we've already seen
+ next_to_search -= state_groups_seen
+ state_groups_seen |= next_to_search
+
+ for row in rows:
+ # Note: Each state group can have at most one prev group
+ graph[row["state_group"]] = row["prev_state_group"]
+
+ to_delete = state_groups_seen - referenced_groups
+
+ to_dedelta = set()
+ for sg in referenced_groups:
+ prev_sg = graph.get(sg)
+ if prev_sg and prev_sg in to_delete:
+ to_dedelta.add(sg)
+
+ return to_delete, to_dedelta
+
class StateStore(StateGroupWorkerStore, BackgroundUpdateStore):
""" Keeps track of the state at a given event.
@@ -1064,6 +1144,7 @@ class StateStore(StateGroupWorkerStore, BackgroundUpdateStore):
STATE_GROUP_DEDUPLICATION_UPDATE_NAME = "state_group_state_deduplication"
STATE_GROUP_INDEX_UPDATE_NAME = "state_group_state_type_index"
CURRENT_STATE_INDEX_UPDATE_NAME = "current_state_members_idx"
+ EVENT_STATE_GROUP_INDEX_UPDATE_NAME = "event_to_state_groups_sg_index"
def __init__(self, db_conn, hs):
super(StateStore, self).__init__(db_conn, hs)
@@ -1082,6 +1163,12 @@ class StateStore(StateGroupWorkerStore, BackgroundUpdateStore):
columns=["state_key"],
where_clause="type='m.room.member'",
)
+ self.register_background_index_update(
+ self.EVENT_STATE_GROUP_INDEX_UPDATE_NAME,
+ index_name="event_to_state_groups_sg_index",
+ table="event_to_state_groups",
+ columns=["state_group"],
+ )
def _store_event_state_mappings_txn(self, txn, events_and_contexts):
state_groups = {}
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