1 files changed, 15 insertions, 0 deletions
diff --git a/synapse/federation/sender/per_destination_queue.py b/synapse/federation/sender/per_destination_queue.py
index a5b36b1827..a7c296e880 100644
--- a/synapse/federation/sender/per_destination_queue.py
+++ b/synapse/federation/sender/per_destination_queue.py
@@ -15,6 +15,7 @@
 # limitations under the License.
 import datetime
 import logging
+import random
 
 from prometheus_client import Counter
 
@@ -36,6 +37,8 @@ from synapse.util.retryutils import NotRetryingDestination, get_retry_limiter
 # 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__)
 
 
@@ -189,6 +192,18 @@ class PerDestinationQueue(object):
 
             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
+                    )
+                    yield self._clock.sleep(sleeptime)
+
                 # We have to keep 2 free slots for presence and rr_edus
                 limit = MAX_EDUS_PER_TRANSACTION - 2