Make opentracing trace into event persistence (#10134)

* Trace event persistence

When we persist a batch of events, set the parent opentracing span to the that
from the request, so that we can trace all the way in.

* changelog

* When we force tracing, set a baggage item

... so that we can check again later.

* Link in both directions between persist_events spans

1 files changed, 2 insertions, 2 deletions

diff --git a/synapse/api/auth.py b/synapse/api/auth.py

index 26a3b38918..cf4333a923 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -207,7 +207,7 @@ class Auth:
 
                 request.requester = user_id
                 if user_id in self._force_tracing_for_users:
-                    opentracing.set_tag(opentracing.tags.SAMPLING_PRIORITY, 1)
+                    opentracing.force_tracing()
                 opentracing.set_tag("authenticated_entity", user_id)
                 opentracing.set_tag("user_id", user_id)
                 opentracing.set_tag("appservice_id", app_service.id)
@@ -260,7 +260,7 @@ class Auth:
 
             request.requester = requester
             if user_info.token_owner in self._force_tracing_for_users:
-                opentracing.set_tag(opentracing.tags.SAMPLING_PRIORITY, 1)
+                opentracing.force_tracing()
             opentracing.set_tag("authenticated_entity", user_info.token_owner)
             opentracing.set_tag("user_id", user_info.user_id)
             if device_id: