diff --git a/synapse/util/caches/snapshot_cache.py b/synapse/util/caches/snapshot_cache.py
deleted file mode 100644
index 8318db8d2c..0000000000
--- a/synapse/util/caches/snapshot_cache.py
+++ /dev/null
@@ -1,94 +0,0 @@
-# -*- coding: utf-8 -*-
-# Copyright 2015, 2016 OpenMarket Ltd
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-# http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-from synapse.util.async_helpers import ObservableDeferred
-
-
-class SnapshotCache(object):
- """Cache for snapshots like the response of /initialSync.
- The response of initialSync only has to be a recent snapshot of the
- server state. It shouldn't matter to clients if it is a few minutes out
- of date.
-
- This caches a deferred response. Until the deferred completes it will be
- returned from the cache. This means that if the client retries the request
- while the response is still being computed, that original response will be
- used rather than trying to compute a new response.
-
- Once the deferred completes it will removed from the cache after 5 minutes.
- We delay removing it from the cache because a client retrying its request
- could race with us finishing computing the response.
-
- Rather than tracking precisely how long something has been in the cache we
- keep two generations of completed responses. Every 5 minutes discard the
- old generation, move the new generation to the old generation, and set the
- new generation to be empty. This means that a result will be in the cache
- somewhere between 5 and 10 minutes.
- """
-
- DURATION_MS = 5 * 60 * 1000 # Cache results for 5 minutes.
-
- def __init__(self):
- self.pending_result_cache = {} # Request that haven't finished yet.
- self.prev_result_cache = {} # The older requests that have finished.
- self.next_result_cache = {} # The newer requests that have finished.
- self.time_last_rotated_ms = 0
-
- def rotate(self, time_now_ms):
- # Rotate once if the cache duration has passed since the last rotation.
- if time_now_ms - self.time_last_rotated_ms >= self.DURATION_MS:
- self.prev_result_cache = self.next_result_cache
- self.next_result_cache = {}
- self.time_last_rotated_ms += self.DURATION_MS
-
- # Rotate again if the cache duration has passed twice since the last
- # rotation.
- if time_now_ms - self.time_last_rotated_ms >= self.DURATION_MS:
- self.prev_result_cache = self.next_result_cache
- self.next_result_cache = {}
- self.time_last_rotated_ms = time_now_ms
-
- def get(self, time_now_ms, key):
- self.rotate(time_now_ms)
- # This cache is intended to deduplicate requests, so we expect it to be
- # missed most of the time. So we just lookup the key in all of the
- # dictionaries rather than trying to short circuit the lookup if the
- # key is found.
- result = self.prev_result_cache.get(key)
- result = self.next_result_cache.get(key, result)
- result = self.pending_result_cache.get(key, result)
- if result is not None:
- return result.observe()
- else:
- return None
-
- def set(self, time_now_ms, key, deferred):
- self.rotate(time_now_ms)
-
- result = ObservableDeferred(deferred)
-
- self.pending_result_cache[key] = result
-
- def shuffle_along(r):
- # When the deferred completes we shuffle it along to the first
- # generation of the result cache. So that it will eventually
- # expire from the rotation of that cache.
- self.next_result_cache[key] = result
- self.pending_result_cache.pop(key, None)
- return r
-
- result.addBoth(shuffle_along)
-
- return result.observe()
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