`claim_e2e_one_time_keys` results in lots of TransactionRollbackError: could not serialize access due to concurrent update

[erikjohnston]

TransactionRollbackError: could not serialize access due to concurrent update

(23 additional frame(s) were not displayed)
...
  File "synapse/storage/_base.py", line 453, in inner_func
    return func(conn, *args, **kwargs)
  File "synapse/storage/_base.py", line 329, in _new_transaction
    r = func(txn, *args, **kwargs)
  File "synapse/storage/end_to_end_keys.py", line 266, in _claim_e2e_one_time_keys
    txn.execute(sql, (user_id, device_id, algorithm, key_id))
  File "synapse/storage/_base.py", line 119, in execute
    self._do_execute(self.txn.execute, sql, *args)
  File "synapse/storage/_base.py", line 149, in _do_execute
    sql, *args

Failed handle request via u'OneTimeKeyServlet': u"<XForwardedForRequest at 0x7f7b35349780 method='POST' uri='/_matrix/client/unstable/keys/claim' clientproto='HTTP/1.1' site=8080>"

Note that this only gets thrown after we've retried 5 times

[uhoreg]

Probably the same as #4868? (I'd be happy to close that one, since this one has more useful information)

[richvdh]

yes, probably the same as #4868.

also related: #4993

[uhoreg]

(as mentioned in #4868) see also #3608