Revert federation-transaction-transmission backoff hacks

This reverts b852a8247, 15b2a5081, 28889d8da.

I don't think these patches are required any more, and if they are, they should
be on mainline, not hidden in our hotfixes branch. Let's try backing them out:
if that turns out to be an error, we can PR them properly.

synapse/federation/sender/__init__.py

@@ -151,25 +151,10 @@ class FederationSender:
             "process_event_queue_for_federation", self._process_event_queue_loop
         )
 
-    async def _process_event_queue_loop(self):
+    async def _process_event_queue_loop(self) -> None:
-        loop_start_time = self.clock.time_msec()
         try:
             self._is_processing = True
             while True:
-                # if we've been going around this loop for a long time without
-                # catching up, deprioritise transaction transmission. This should mean
-                # that events get batched into fewer transactions, which is more
-                # efficient, and hence give us a chance to catch up
-                if (
-                    self.clock.time_msec() - loop_start_time > 60 * 1000
-                    and not self._transaction_manager.deprioritise_transmission
-                ):
-                    logger.warning(
-                        "Event queue is getting behind: deprioritising transaction "
-                        "transmission"
-                    )
-                    self._transaction_manager.deprioritise_transmission = True
-
                 last_token = await self.store.get_federation_out_pos("events")
                 next_token, events = await self.store.get_all_new_events_stream(
                     last_token, self._last_poked_id, limit=100
@@ -279,9 +264,6 @@ class FederationSender:
 
         finally:
             self._is_processing = False
-            if self._transaction_manager.deprioritise_transmission:
-                logger.info("Event queue caught up: re-prioritising transmission")
-                self._transaction_manager.deprioritise_transmission = False
 
     def _send_pdu(self, pdu: EventBase, destinations: Iterable[str]) -> None:
         # We loop through all destinations to see whether we already have

synapse/federation/sender/per_destination_queue.py

@@ -15,7 +15,6 @@
 # limitations under the License.
 import datetime
 import logging
-import random
 from typing import TYPE_CHECKING, Dict, Hashable, Iterable, List, Tuple
 
 from prometheus_client import Counter
@@ -40,8 +39,6 @@ if TYPE_CHECKING:
 # This is defined in the Matrix spec and enforced by the receiver.
 MAX_EDUS_PER_TRANSACTION = 100
 
-DEPRIORITISE_SLEEP_TIME = 10
-
 logger = logging.getLogger(__name__)
 
 
@@ -223,18 +220,6 @@ class PerDestinationQueue:
 
             pending_pdus = []
             while True:
-                if self._transaction_manager.deprioritise_transmission:
-                    # if the event-processing loop has got behind, sleep to give it
-                    # a chance to catch up. Add some randomness so that the transmitters
-                    # don't all wake up in sync.
-                    sleeptime = random.uniform(
-                        DEPRIORITISE_SLEEP_TIME, DEPRIORITISE_SLEEP_TIME * 2
-                    )
-                    logger.info(
-                        "TX [%s]: sleeping for %f seconds", self._destination, sleeptime
-                    )
-                    await self._clock.sleep(sleeptime)
-
                 # We have to keep 2 free slots for presence and rr_edus
                 limit = MAX_EDUS_PER_TRANSACTION - 2
 

synapse/federation/sender/transaction_manager.py

@@ -51,10 +51,6 @@ class TransactionManager:
         # HACK to get unique tx id
         self._next_txn_id = int(self.clock.time_msec())
 
-        # the federation sender sometimes sets this to delay transaction transmission,
-        # if the sender gets behind.
-        self.deprioritise_transmission = False
-
     @measure_func("_send_new_transaction")
     async def send_new_transaction(
         self, destination: str, pdus: List[EventBase], edus: List[Edu],