Add prometheus exemplars support

2 files changed, 12 insertions, 1 deletions

diff --git a/synapse/http/request_metrics.py b/synapse/http/request_metrics.py
index 2b6d113544..4acb30e1db 100644
--- a/synapse/http/request_metrics.py
+++ b/synapse/http/request_metrics.py
@@ -21,6 +21,7 @@ from typing import Dict, Mapping, Set, Tuple
 from prometheus_client.core import Counter, Histogram
 
 from synapse.logging.context import current_context
+from synapse.logging.opentracing import get_prometheus_exemplar
 from synapse.metrics import LaterGauge
 
 logger = logging.getLogger(__name__)
@@ -193,7 +194,7 @@ class RequestMetrics:
         response_count.labels(self.method, self.name, tag).inc()
 
         response_timer.labels(self.method, self.name, tag, response_code_str).observe(
-            time_sec - self.start_ts
+            time_sec - self.start_ts, exemplar=get_prometheus_exemplar()
         )
 
         resource_usage = context.get_resource_usage()
diff --git a/synapse/logging/opentracing.py b/synapse/logging/opentracing.py
index be910128aa..f5e4993fab 100644
--- a/synapse/logging/opentracing.py
+++ b/synapse/logging/opentracing.py
@@ -672,6 +672,16 @@ def active_span() -> Optional["opentracing.Span"]:
     return opentracing.tracer.active_span
 
 
+def get_prometheus_exemplar() -> Optional[Dict[str, str]]:
+    span = active_span()
+    if not span:
+        return None
+
+    trace_id = getattr(span, "trace_id", None)
+
+    return trace_id
+
+
 @ensure_active_span("set a tag")
 def set_tag(key: str, value: Union[str, bool, int, float]) -> None:
     """Sets a tag on the active span"""