235 lines
8.4 KiB
Python
235 lines
8.4 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2015, 2016 OpenMarket Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import logging
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import random
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import synapse.logging.context
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from synapse.api.errors import CodeMessageException
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logger = logging.getLogger(__name__)
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# the initial backoff, after the first transaction fails
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MIN_RETRY_INTERVAL = 10 * 60 * 1000
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# how much we multiply the backoff by after each subsequent fail
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RETRY_MULTIPLIER = 5
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# a cap on the backoff. (Essentially none)
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MAX_RETRY_INTERVAL = 2 ** 62
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class NotRetryingDestination(Exception):
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def __init__(self, retry_last_ts, retry_interval, destination):
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"""Raised by the limiter (and federation client) to indicate that we are
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are deliberately not attempting to contact a given server.
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Args:
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retry_last_ts (int): the unix ts in milliseconds of our last attempt
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to contact the server. 0 indicates that the last attempt was
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successful or that we've never actually attempted to connect.
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retry_interval (int): the time in milliseconds to wait until the next
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attempt.
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destination (str): the domain in question
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"""
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msg = "Not retrying server %s." % (destination,)
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super().__init__(msg)
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self.retry_last_ts = retry_last_ts
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self.retry_interval = retry_interval
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self.destination = destination
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async def get_retry_limiter(destination, clock, store, ignore_backoff=False, **kwargs):
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"""For a given destination check if we have previously failed to
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send a request there and are waiting before retrying the destination.
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If we are not ready to retry the destination, this will raise a
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NotRetryingDestination exception. Otherwise, will return a Context Manager
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that will mark the destination as down if an exception is thrown (excluding
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CodeMessageException with code < 500)
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Args:
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destination (str): name of homeserver
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clock (synapse.util.clock): timing source
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store (synapse.storage.transactions.TransactionStore): datastore
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ignore_backoff (bool): true to ignore the historical backoff data and
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try the request anyway. We will still reset the retry_interval on success.
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Example usage:
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try:
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limiter = await get_retry_limiter(destination, clock, store)
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with limiter:
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response = await do_request()
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except NotRetryingDestination:
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# We aren't ready to retry that destination.
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raise
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"""
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failure_ts = None
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retry_last_ts, retry_interval = (0, 0)
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retry_timings = await store.get_destination_retry_timings(destination)
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if retry_timings:
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failure_ts = retry_timings["failure_ts"]
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retry_last_ts, retry_interval = (
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retry_timings["retry_last_ts"],
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retry_timings["retry_interval"],
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)
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now = int(clock.time_msec())
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if not ignore_backoff and retry_last_ts + retry_interval > now:
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raise NotRetryingDestination(
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retry_last_ts=retry_last_ts,
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retry_interval=retry_interval,
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destination=destination,
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)
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# if we are ignoring the backoff data, we should also not increment the backoff
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# when we get another failure - otherwise a server can very quickly reach the
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# maximum backoff even though it might only have been down briefly
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backoff_on_failure = not ignore_backoff
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return RetryDestinationLimiter(
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destination,
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clock,
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store,
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failure_ts,
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retry_interval,
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backoff_on_failure=backoff_on_failure,
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**kwargs,
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)
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class RetryDestinationLimiter:
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def __init__(
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self,
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destination,
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clock,
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store,
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failure_ts,
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retry_interval,
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backoff_on_404=False,
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backoff_on_failure=True,
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):
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"""Marks the destination as "down" if an exception is thrown in the
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context, except for CodeMessageException with code < 500.
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If no exception is raised, marks the destination as "up".
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Args:
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destination (str)
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clock (Clock)
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store (DataStore)
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failure_ts (int|None): when this destination started failing (in ms since
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the epoch), or zero if the last request was successful
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retry_interval (int): The next retry interval taken from the
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database in milliseconds, or zero if the last request was
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successful.
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backoff_on_404 (bool): Back off if we get a 404
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backoff_on_failure (bool): set to False if we should not increase the
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retry interval on a failure.
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"""
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self.clock = clock
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self.store = store
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self.destination = destination
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self.failure_ts = failure_ts
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self.retry_interval = retry_interval
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self.backoff_on_404 = backoff_on_404
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self.backoff_on_failure = backoff_on_failure
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def __enter__(self):
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pass
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def __exit__(self, exc_type, exc_val, exc_tb):
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valid_err_code = False
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if exc_type is None:
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valid_err_code = True
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elif not issubclass(exc_type, Exception):
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# avoid treating exceptions which don't derive from Exception as
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# failures; this is mostly so as not to catch defer._DefGen.
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valid_err_code = True
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elif issubclass(exc_type, CodeMessageException):
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# Some error codes are perfectly fine for some APIs, whereas other
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# APIs may expect to never received e.g. a 404. It's important to
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# handle 404 as some remote servers will return a 404 when the HS
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# has been decommissioned.
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# If we get a 401, then we should probably back off since they
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# won't accept our requests for at least a while.
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# 429 is us being aggressively rate limited, so lets rate limit
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# ourselves.
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if exc_val.code == 404 and self.backoff_on_404:
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valid_err_code = False
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elif exc_val.code in (401, 429):
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valid_err_code = False
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elif exc_val.code < 500:
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valid_err_code = True
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else:
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valid_err_code = False
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if valid_err_code:
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# We connected successfully.
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if not self.retry_interval:
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return
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logger.debug(
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"Connection to %s was successful; clearing backoff", self.destination
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)
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self.failure_ts = None
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retry_last_ts = 0
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self.retry_interval = 0
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elif not self.backoff_on_failure:
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return
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else:
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# We couldn't connect.
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if self.retry_interval:
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self.retry_interval = int(
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self.retry_interval * RETRY_MULTIPLIER * random.uniform(0.8, 1.4)
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)
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if self.retry_interval >= MAX_RETRY_INTERVAL:
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self.retry_interval = MAX_RETRY_INTERVAL
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else:
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self.retry_interval = MIN_RETRY_INTERVAL
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logger.info(
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"Connection to %s was unsuccessful (%s(%s)); backoff now %i",
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self.destination,
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exc_type,
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exc_val,
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self.retry_interval,
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)
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retry_last_ts = int(self.clock.time_msec())
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if self.failure_ts is None:
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self.failure_ts = retry_last_ts
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async def store_retry_timings():
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try:
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await self.store.set_destination_retry_timings(
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self.destination,
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self.failure_ts,
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retry_last_ts,
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self.retry_interval,
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)
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except Exception:
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logger.exception("Failed to store destination_retry_timings")
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# we deliberately do this in the background.
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synapse.logging.context.run_in_background(store_retry_timings)
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