Fix errors storing large retry intervals.

We have set the max retry interval to a value larger than a postgres or
sqlite int can hold, which caused exceptions when updating the
destinations table.

To fix postgres we need to change the column to a bigint, and for sqlite
we lower the max interval to 2**62 (which is still incredibly long).

synapse/storage/schema/delta/56/destinations_retry_interval_type.sql.postgres

+/* Copyright 2019 The Matrix.org Foundation C.I.C
+ *
+ * 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.
+ */
+
+-- We want to store large retry intervals so we upgrade the column from INT
+-- to BIGINT. We don't need to do this on SQLite.
+ALTER TABLE destinations ALTER retry_interval SET DATA TYPE BIGINT;

synapse/util/retryutils.py

@@ -29,7 +29,7 @@ MIN_RETRY_INTERVAL = 10 * 60 * 1000
 RETRY_MULTIPLIER = 5
 
 # a cap on the backoff. (Essentially none)
-MAX_RETRY_INTERVAL = 2 ** 63
+MAX_RETRY_INTERVAL = 2 ** 62
 
 
 class NotRetryingDestination(Exception):

tests/storage/test_transactions.py

@@ -13,6 +13,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from synapse.util.retryutils import MAX_RETRY_INTERVAL
+
 from tests.unittest import HomeserverTestCase
 
 
@@ -45,3 +47,12 @@ class TransactionStoreTestCase(HomeserverTestCase):
         """
         d = self.store.set_destination_retry_timings("example.com", 1000, 50, 100)
         self.get_success(d)
+
+    def test_large_destination_retry(self):
+        d = self.store.set_destination_retry_timings(
+            "example.com", MAX_RETRY_INTERVAL, MAX_RETRY_INTERVAL, MAX_RETRY_INTERVAL
+        )
+        self.get_success(d)
+
+        d = self.store.get_destination_retry_timings("example.com")
+        self.get_success(d)