diff options
Diffstat (limited to 'synapse/storage')
| -rw-r--r-- | synapse/storage/data_stores/main/event_federation.py | 150 |
1 files changed, 149 insertions, 1 deletions
diff --git a/synapse/storage/data_stores/main/event_federation.py b/synapse/storage/data_stores/main/event_federation.py index 49a7b8b433..62d4e9f599 100644 --- a/synapse/storage/data_stores/main/event_federation.py +++ b/synapse/storage/data_stores/main/event_federation.py @@ -14,7 +14,7 @@ # limitations under the License. import itertools import logging -from typing import List, Optional, Set +from typing import Dict, List, Optional, Set, Tuple from six.moves.queue import Empty, PriorityQueue @@ -103,6 +103,154 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore, SQLBas return list(results) + def get_auth_chain_difference(self, state_sets: List[Set[str]]): + """Given sets of state events figure out the auth chain difference (as + per state res v2 algorithm). + + This equivalent to fetching the full auth chain for each set of state + and returning the events that don't appear in each and every auth + chain. + + Returns: + Deferred[Set[str]] + """ + + return self.db.runInteraction( + "get_auth_chain_difference", + self._get_auth_chain_difference_txn, + state_sets, + ) + + def _get_auth_chain_difference_txn( + self, txn, state_sets: List[Set[str]] + ) -> Set[str]: + + # Algorithm Description + # ~~~~~~~~~~~~~~~~~~~~~ + # + # The idea here is to basically walk the auth graph of each state set in + # tandem, keeping track of which auth events are reachable by each state + # set. If we reach an auth event we've already visited (via a different + # state set) then we mark that auth event and all ancestors as reachable + # by the state set. This requires that we keep track of the auth chains + # in memory. + # + # Doing it in a such a way means that we can stop early if all auth + # events we're currently walking are reachable by all state sets. + # + # *Note*: We can't stop walking an event's auth chain if it is reachable + # by all state sets. This is because other auth chains we're walking + # might be reachable only via the original auth chain. For example, + # given the following auth chain: + # + # A -> C -> D -> E + # / / + # B -´---------´ + # + # and state sets {A} and {B} then walking the auth chains of A and B + # would immediately show that C is reachable by both. However, if we + # stopped at C then we'd only reach E via the auth chain of B and so E + # would errornously get included in the returned difference. + # + # The other thing that we do is limit the number of auth chains we walk + # at once, due to practical limits (i.e. we can only query the database + # with a limited set of parameters). We pick the auth chains we walk + # each iteration based on their depth, in the hope that events with a + # lower depth are likely reachable by those with higher depths. + # + # We could use any ordering that we believe would give a rough + # topological ordering, e.g. origin server timestamp. If the ordering + # chosen is not topological then the algorithm still produces the right + # result, but perhaps a bit more inefficiently. This is why it is safe + # to use "depth" here. + + initial_events = set(state_sets[0]).union(*state_sets[1:]) + + # Dict from events in auth chains to which sets *cannot* reach them. + # I.e. if the set is empty then all sets can reach the event. + event_to_missing_sets = { + event_id: {i for i, a in enumerate(state_sets) if event_id not in a} + for event_id in initial_events + } + + # We need to get the depth of the initial events for sorting purposes. + sql = """ + SELECT depth, event_id FROM events + WHERE %s + ORDER BY depth ASC + """ + clause, args = make_in_list_sql_clause( + txn.database_engine, "event_id", initial_events + ) + txn.execute(sql % (clause,), args) + + # The sorted list of events whose auth chains we should walk. + search = txn.fetchall() # type: List[Tuple[int, str]] + + # Map from event to its auth events + event_to_auth_events = {} # type: Dict[str, Set[str]] + + base_sql = """ + SELECT a.event_id, auth_id, depth + FROM event_auth AS a + INNER JOIN events AS e ON (e.event_id = a.auth_id) + WHERE + """ + + while search: + # Check whether all our current walks are reachable by all state + # sets. If so we can bail. + if all(not event_to_missing_sets[eid] for _, eid in search): + break + + # Fetch the auth events and their depths of the N last events we're + # currently walking + search, chunk = search[:-100], search[-100:] + clause, args = make_in_list_sql_clause( + txn.database_engine, "a.event_id", [e_id for _, e_id in chunk] + ) + txn.execute(base_sql + clause, args) + + for event_id, auth_event_id, auth_event_depth in txn: + event_to_auth_events.setdefault(event_id, set()).add(auth_event_id) + + sets = event_to_missing_sets.get(auth_event_id) + if sets is None: + # First time we're seeing this event, so we add it to the + # queue of things to fetch. + search.append((auth_event_depth, auth_event_id)) + + # Assume that this event is unreachable from any of the + # state sets until proven otherwise + sets = event_to_missing_sets[auth_event_id] = set( + range(len(state_sets)) + ) + else: + # We've previously seen this event, so look up its auth + # events and recursively mark all ancestors as reachable + # by the current event's state set. + a_ids = event_to_auth_events.get(auth_event_id) + while a_ids: + new_aids = set() + for a_id in a_ids: + event_to_missing_sets[a_id].intersection_update( + event_to_missing_sets[event_id] + ) + + b = event_to_auth_events.get(a_id) + if b: + new_aids.update(b) + + a_ids = new_aids + + # Mark that the auth event is reachable by the approriate sets. + sets.intersection_update(event_to_missing_sets[event_id]) + + search.sort() + + # Return all events where not all sets can reach them. + return {eid for eid, n in event_to_missing_sets.items() if n} + def get_oldest_events_in_room(self, room_id): return self.db.runInteraction( "get_oldest_events_in_room", self._get_oldest_events_in_room_txn, room_id |