Instrument `/messages` for understandable traces in Jaeger (#13368)

In Jaeger:

 - Before: huge list of uncategorized database calls
 - After: nice and collapsible into units of work

1 files changed, 5 insertions, 0 deletions

diff --git a/synapse/handlers/federation_event.py b/synapse/handlers/federation_event.py
index 91d1439191..8968b705d4 100644
--- a/synapse/handlers/federation_event.py
+++ b/synapse/handlers/federation_event.py
@@ -59,6 +59,7 @@ from synapse.events import EventBase
 from synapse.events.snapshot import EventContext
 from synapse.federation.federation_client import InvalidResponseError
 from synapse.logging.context import nested_logging_context
+from synapse.logging.opentracing import trace
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.replication.http.devices import ReplicationUserDevicesResyncRestServlet
 from synapse.replication.http.federation import (
@@ -566,6 +567,7 @@ class FederationEventHandler:
                 event.event_id
             )
 
+    @trace
     async def backfill(
         self, dest: str, room_id: str, limit: int, extremities: Collection[str]
     ) -> None:
@@ -610,6 +612,7 @@ class FederationEventHandler:
             backfilled=True,
         )
 
+    @trace
     async def _get_missing_events_for_pdu(
         self, origin: str, pdu: EventBase, prevs: Set[str], min_depth: int
     ) -> None:
@@ -710,6 +713,7 @@ class FederationEventHandler:
         logger.info("Got %d prev_events", len(missing_events))
         await self._process_pulled_events(origin, missing_events, backfilled=False)
 
+    @trace
     async def _process_pulled_events(
         self, origin: str, events: Iterable[EventBase], backfilled: bool
     ) -> None:
@@ -748,6 +752,7 @@ class FederationEventHandler:
             with nested_logging_context(ev.event_id):
                 await self._process_pulled_event(origin, ev, backfilled=backfilled)
 
+    @trace
     async def _process_pulled_event(
         self, origin: str, event: EventBase, backfilled: bool
     ) -> None: