fix: use debug logging level for OpenTelemetry message (#442)

* fix: use debug logging level for OpenTelemetry message

* only warn at span creation time

* add unit test for skipping warning

* refactor: rename _warned_telemetry to indicate private and mutable

google/cloud/bigquery/opentelemetry_tracing.py

@@ -23,16 +23,11 @@
     from opentelemetry.trace.status import Status
 
     HAS_OPENTELEMETRY = True
+    _warned_telemetry = True
 
 except ImportError:
-    logger.info(
-        "This service is instrumented using OpenTelemetry. "
-        "OpenTelemetry could not be imported; please "
-        "add opentelemetry-api and opentelemetry-instrumentation "
-        "packages in order to get BigQuery Tracing data."
-    )
-
     HAS_OPENTELEMETRY = False
+    _warned_telemetry = False
 
 _default_attributes = {
     "db.system": "BigQuery"
@@ -64,8 +59,18 @@ def create_span(name, attributes=None, client=None, job_ref=None):
                     Raised if a span could not be yielded or issue with call to
                     OpenTelemetry.
             """
+    global _warned_telemetry
     final_attributes = _get_final_span_attributes(attributes, client, job_ref)
     if not HAS_OPENTELEMETRY:
+        if not _warned_telemetry:
+            logger.debug(
+                "This service is instrumented using OpenTelemetry. "
+                "OpenTelemetry could not be imported; please "
+                "add opentelemetry-api and opentelemetry-instrumentation "
+                "packages in order to get BigQuery Tracing data."
+            )
+            _warned_telemetry = True
+
         yield None
         return
     tracer = trace.get_tracer(__name__)

tests/unit/test_opentelemetry_tracing.py

@@ -52,8 +52,20 @@ def setup():
 def test_opentelemetry_not_installed(setup, monkeypatch):
     monkeypatch.setitem(sys.modules, "opentelemetry", None)
     importlib.reload(opentelemetry_tracing)
+    assert not opentelemetry_tracing._warned_telemetry
     with opentelemetry_tracing.create_span("No-op for opentelemetry") as span:
         assert span is None
+        assert opentelemetry_tracing._warned_telemetry
+
+
+@pytest.mark.skipif(opentelemetry is None, reason="Require `opentelemetry`")
+def test_opentelemetry_not_installed_doesnt_warn(setup, monkeypatch):
+    monkeypatch.setitem(sys.modules, "opentelemetry", None)
+    importlib.reload(opentelemetry_tracing)
+    opentelemetry_tracing._warned_telemetry = True
+    with opentelemetry_tracing.create_span("No-op for opentelemetry") as span:
+        assert span is None
+        assert opentelemetry_tracing._warned_telemetry
 
 
 @pytest.mark.skipif(opentelemetry is None, reason="Require `opentelemetry`")