Change default Sampler to ParentOrElse(AlwaysOn) (#960)

Author: MitchellDumovic

opentelemetry-sdk/CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Changed default Sampler to `ParentOrElse(AlwaysOn)`
 - Update environment variable names, prefix changed from `OPENTELEMETRY` to `OTEL`
   ([#904](https://github.com/open-telemetry/opentelemetry-python/pull/904))
 - Implement Views in metrics SDK

opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py

@@ -859,7 +859,7 @@ def use_span(
 class TracerProvider(trace_api.TracerProvider):
     def __init__(
         self,
-        sampler: sampling.Sampler = trace_api.sampling.ALWAYS_ON,
+        sampler: sampling.Sampler = trace_api.sampling.DEFAULT_ON,
         resource: Resource = Resource.create_empty(),
         shutdown_on_exit: bool = True,
         active_span_processor: Union[

opentelemetry-sdk/tests/trace/test_trace.py

@@ -344,6 +344,7 @@ def test_start_as_current_span_explicit(self):
             trace_id=0x000000000000000000000000DEADBEEF,
             span_id=0x00000000DEADBEF0,
             is_remote=False,
+            trace_flags=trace_api.TraceFlags(trace_api.TraceFlags.SAMPLED),
         )
 
         self.assertEqual(trace_api.get_current_span(), trace_api.INVALID_SPAN)