From 2318603772f2e1595f9b39369246d5955a069381 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Thu, 1 Sep 2022 14:54:52 +0200
Subject: [PATCH] Add some logging to help track down #13444 (#13679)

---
 changelog.d/13679.misc                |  1 +
 synapse/federation/sender/__init__.py | 13 +++++++++++++
 2 files changed, 14 insertions(+)
 create mode 100644 changelog.d/13679.misc

diff --git a/changelog.d/13679.misc b/changelog.d/13679.misc
new file mode 100644
index 000000000..a4fa94da9
--- /dev/null
+++ b/changelog.d/13679.misc
@@ -0,0 +1 @@
+Add some logging to help track down #13444.
diff --git a/synapse/federation/sender/__init__.py b/synapse/federation/sender/__init__.py
index 94a65ac65..8bc60e3e3 100644
--- a/synapse/federation/sender/__init__.py
+++ b/synapse/federation/sender/__init__.py
@@ -441,6 +441,19 @@ class FederationSender(AbstractFederationSender):
                             destinations = await self._external_cache.get(
                                 "get_joined_hosts", str(sg)
                             )
+                            if destinations is None:
+                                # Add logging to help track down #13444
+                                logger.info(
+                                    "Unexpectedly did not have cached destinations for %s / %s",
+                                    sg,
+                                    event.event_id,
+                                )
+                        else:
+                            # Add logging to help track down #13444
+                            logger.info(
+                                "Unexpectedly did not have cached prev group for %s",
+                                event.event_id,
+                            )
 
                     if destinations is None:
                         try: