Error: Event has no state groups

[turt2live]

Unclear severity. This is on the develop branch as of writing. Happens to several events in different rooms at different times (not a pattern).

er - 2018-07-25 06:20:39,274 - synapse.storage.events - 422 - INFO - Calculating state delta for room !redacted:matrix.org
homeserver - 2018-07-25 06:20:39,275 - synapse.util.async - 250 - INFO - Releasing linearizer lock 'fed_room_pdu' for key '!redacted:matrix.org'
homeserver - 2018-07-25 06:20:39,275 - synapse.federation.federation_server - 194 - ERROR - Failed to handle PDU $redacted:matrix.org: Traceback (most recent call last):
--- <exception caught here> ---
  File "/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/federation/federation_server.py", line 183, in process_pdus_for_room
    transaction.origin, pdu
  File "/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/federation/federation_server.py", line 605, in _handle_received_pdu
    origin, pdu, get_missing=True, sent_to_us_directly=True,
  File "/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/handlers/federation.py", line 213, in on_receive_pdu
    origin, pdu, prevs, min_depth
  File "/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/handlers/federation.py", line 366, in _get_missing_events_for_pdu
    get_missing=False
  File "/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/handlers/federation.py", line 290, in on_receive_pdu
    auth_chain=auth_chain,
  File "/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/handlers/federation.py", line 444, in _process_received_pdu
    yield self._handle_new_events(origin, event_infos)
  File "/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/handlers/federation.py", line 1525, in _handle_new_events
    backfilled=backfilled,
twisted.internet.defer.FirstError: FirstError[#0, [Failure instance: Traceback: <type 'exceptions.Exception'>: Context for new extremity event $redacted:matrix.org has no state group
/home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py:1418:_inlineCallbacks
/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/storage/events.py:432:_persist_events
/home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py:1613:unwindGenerator
/home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py:1529:_cancellableInlineCallbacks
--- <exception caught here> ---
/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/storage/events.py:149:handle_queue_loop
/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/storage/events.py:293:persisting_queue
/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/storage/events.py:188:f
/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/storage/events.py:432:_persist_events
/home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py:1418:_inlineCallbacks
/home/matrix/.synapse/local/lib/python2.7/site-packages/synapse/storage/events.py:581:_get_new_state_after_events
]]
homeserver - 2018-07-25 06:20:39,283 - synapse.util.logcontext - 273 - WARNING - Expected logging context persist_events@7fccd36db488 has been lost

[erikjohnston]

The linked PR should fix this.

Broadly this was happening when we were persisting outlier events during the same persist event loop as non-outlier events for the room. The non-outlier events forced it down the code path of recalculating current state, at which point we asserted that all event contexts must have a state group. Outlier events don't have a state group.

[richvdh]

(the logcontext leak is fixed in #3606)

[turt2live]

Looks like #3603 did fix it. Also the log context warning is gone. Thanks!