Change sampling rule of FixedRateSampler (#48)

Author: liyanhui1228

trace/opencensus/trace/request_tracer.py

@@ -74,7 +74,7 @@ def should_sample(self):
         :returns: Whether to trace the request or not.
         """
         return self.span_context.trace_options.enabled \
-            and self.sampler.should_sample
+            and self.sampler.should_sample(self.span_context.trace_id)
 
     def get_tracer(self):
         """Return a tracer according to the sampling decision."""

trace/opencensus/trace/samplers/always_off.py

@@ -17,7 +17,6 @@
 
 class AlwaysOffSampler(Sampler):
 
-    @property
-    def should_sample(self):
+    def should_sample(self, trace_id):
         """Always return False because we don't want to sample."""
         return False

trace/opencensus/trace/samplers/always_on.py

@@ -17,7 +17,6 @@
 
 class AlwaysOnSampler(Sampler):
 
-    @property
-    def should_sample(self):
+    def should_sample(self, trace_id):
         """Always return True because we want to sampler all requests."""
         return True

trace/opencensus/trace/samplers/base.py

@@ -21,7 +21,6 @@ class Sampler(object):
     Subclasses of :class:`Sampler` must override :meth:`should_sample`.
     """
 
-    @property
-    def should_sample(self):
+    def should_sample(self, trace_id):
         """Determine whether to sample this request or not."""
         raise NotImplementedError

trace/opencensus/trace/samplers/fixed_rate.py

@@ -12,30 +12,46 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import random
-
 from opencensus.trace.samplers.base import Sampler
 
 DEFAULT_SAMPLING_RATE = 0.5
 
+MAX_VALUE = 0xffffffffffffffff
+
 
 class FixedRateSampler(Sampler):
     """Sample a request at a fixed rate.
 
     :type rate: float
     :param rate: The rate of sampling.
     """
-    def __init__(self, rate=DEFAULT_SAMPLING_RATE):
+    def __init__(self, rate=None):
+        if rate is None:
+            rate = DEFAULT_SAMPLING_RATE
+
         if rate > 1 or rate < 0:
             raise ValueError('Rate must between 0 and 1.')
 
         self.rate = rate
 
-    @property
-    def should_sample(self):
-        random_number = random.uniform(0, 1)
+    def should_sample(self, trace_id):
+        lower_long = get_lower_long_from_trace_id(trace_id)
+        bound = self.rate * MAX_VALUE
 
-        if random_number <= self.rate:
+        if lower_long <= bound:
             return True
         else:
             return False
+
+
+def get_lower_long_from_trace_id(trace_id):
+    """Returns the lower 8 bytes of the trace ID as a long value, assuming
+    little endian order.
+
+    :rtype: long
+    :returns: Lower 8 bytes of trace ID
+    """
+    lower_bytes = trace_id[16:]
+    lower_long = int(lower_bytes, 16)
+
+    return lower_long

trace/tests/unit/samplers/test_always_off.py

@@ -20,6 +20,6 @@ def test_should_sample(self):
         from opencensus.trace.samplers import always_off
 
         sampler = always_off.AlwaysOffSampler()
-        should_sample = sampler.should_sample
+        should_sample = sampler.should_sample(trace_id='fake_id')
 
         self.assertFalse(should_sample)

trace/tests/unit/samplers/test_always_on.py

@@ -20,6 +20,6 @@ def test_should_sample(self):
         from opencensus.trace.samplers import always_on
 
         sampler = always_on.AlwaysOnSampler()
-        should_sample = sampler.should_sample
+        should_sample = sampler.should_sample(trace_id='fake_id')
 
         self.assertTrue(should_sample)

trace/tests/unit/samplers/test_base_sampler.py

@@ -22,4 +22,4 @@ def test_should_sample_abstract(self):
         sampler = base.Sampler()
 
         with self.assertRaises(NotImplementedError):
-            sampler.should_sample()
+            sampler.should_sample(trace_id='fake_id')

trace/tests/unit/samplers/test_fixed_rate.py

@@ -24,19 +24,43 @@ def test_constructor_invalid(self):
             fixed_rate.FixedRateSampler(rate=2)
 
     def test_constructor_valid(self):
-        rate = 0.5
+        rate = 0.8
+        trace_id = 'f8739df974a4481f98748cd92b27177d'
         sampler = fixed_rate.FixedRateSampler(rate=rate)
 
         self.assertEqual(sampler.rate, rate)
 
+    def test_constructor_default(self):
+        rate = 0.5
+        trace_id = 'f8739df974a4481f98748cd92b27177d'
+        sampler = fixed_rate.FixedRateSampler()
+
+        self.assertEqual(sampler.rate, rate)
+
     def test_should_sample_smaller(self):
+        trace_id = 'f8739df974a4481f98748cd92b27177d'
         sampler = fixed_rate.FixedRateSampler(rate=1)
-        should_sample = sampler.should_sample
+        should_sample = sampler.should_sample(trace_id=trace_id)
 
         self.assertTrue(should_sample)
 
     def test_should_sample_greater(self):
+        trace_id = 'f8739df974a4481f98748cd92b27177d'
         sampler = fixed_rate.FixedRateSampler(rate=0)
-        should_sample = sampler.should_sample
+        should_sample = sampler.should_sample(trace_id=trace_id)
+
+        self.assertFalse(should_sample)
+
+    def test_should_sample_trace_id_sampled(self):
+        trace_id = '00000000000000000000000000000000'
+        sampler = fixed_rate.FixedRateSampler(rate=0.5)
+        should_sample = sampler.should_sample(trace_id=trace_id)
+
+        self.assertTrue(should_sample)
+
+    def test_should_sample_trace_id_not_sampled(self):
+        trace_id = 'ffffffffffffffffffffffffffffffff'
+        sampler = fixed_rate.FixedRateSampler(rate=0.5)
+        should_sample = sampler.should_sample(trace_id=trace_id)
 
         self.assertFalse(should_sample)

trace/tests/unit/test_request_tracer.py

@@ -42,7 +42,7 @@ def test_constructor_explicit(self):
         from opencensus.trace.tracer import noop_tracer
 
         sampler = mock.Mock()
-        sampler.should_sample = False
+        sampler.should_sample.return_value = False
 
         exporter = mock.Mock()
         propagator = mock.Mock()
@@ -73,15 +73,15 @@ def test_should_sample_force_not_trace(self):
 
     def test_should_sample_sampled(self):
         sampler =mock.Mock()
-        sampler.should_sample = True
+        sampler.should_sample.return_value = True
         tracer = request_tracer.RequestTracer(sampler=sampler)
         sampled = tracer.should_sample()
 
         self.assertTrue(sampled)
 
     def test_should_sample_not_sampled(self):
         sampler = mock.Mock()
-        sampler.should_sample = False
+        sampler.should_sample.return_value = False
         tracer = request_tracer.RequestTracer(sampler=sampler)
         sampled = tracer.should_sample()
 
@@ -91,7 +91,7 @@ def get_tracer_noop_tracer(self):
         from opencensus.trace.tracer import noop_tracer
 
         sampler = mock.Mock()
-        sampler.should_sample = False
+        sampler.should_sample.return_value = False
         tracer = request_tracer.RequestTracer(sampler=sampler)
 
         result = tracer.get_tracer()
@@ -102,7 +102,7 @@ def get_tracer_context_tracer(self):
         from opencensus.trace.tracer import context_tracer
 
         sampler = mock.Mock()
-        sampler.should_sample = True
+        sampler.should_sample.return_value = True
         tracer = request_tracer.RequestTracer(sampler=sampler)
 
         result = tracer.get_tracer()
@@ -113,7 +113,7 @@ def test_finish_not_sampled(self):
         from opencensus.trace.tracer import noop_tracer
 
         sampler = mock.Mock()
-        sampler.should_sample = False
+        sampler.should_sample.return_value = False
         tracer = request_tracer.RequestTracer(sampler=sampler)
         assert isinstance(tracer.tracer, noop_tracer.NoopTracer)
         mock_tracer = mock.Mock()
@@ -125,7 +125,7 @@ def test_finish_sampled(self):
         from opencensus.trace.tracer import context_tracer
 
         sampler = mock.Mock()
-        sampler.should_sample = True
+        sampler.should_sample.return_value = True
         tracer = request_tracer.RequestTracer(sampler=sampler)
         assert isinstance(tracer.tracer, context_tracer.ContextTracer)
         mock_tracer = mock.Mock()
@@ -137,15 +137,15 @@ def test_span_not_sampled(self):
         from opencensus.trace.tracer import base
 
         sampler = mock.Mock()
-        sampler.should_sample = False
+        sampler.should_sample.return_value = False
         tracer = request_tracer.RequestTracer(sampler=sampler)
 
         span = tracer.span()
         assert isinstance(span, base.NullContextManager)
 
     def test_span_sampled(self):
         sampler = mock.Mock()
-        sampler.should_sample = True
+        sampler.should_sample.return_value = True
         tracer = request_tracer.RequestTracer(sampler=sampler)
         tracer_mock = mock.Mock()
         tracer.tracer = tracer_mock
@@ -158,7 +158,7 @@ def test_start_span_not_sampled(self):
         from opencensus.trace.tracer import base
 
         sampler = mock.Mock()
-        sampler.should_sample = False
+        sampler.should_sample.return_value = False
         tracer = request_tracer.RequestTracer(sampler=sampler)
 
         span = tracer.start_span()
@@ -169,15 +169,15 @@ def test_start_span_sampled(self):
         from opencensus.trace import span as trace_span
 
         sampler = mock.Mock()
-        sampler.should_sample = True
+        sampler.should_sample.return_value = True
         tracer = request_tracer.RequestTracer(sampler=sampler)
         span = tracer.start_span()
 
         assert isinstance(span, trace_span.Span)
 
     def test_end_span_not_sampled(self):
         sampler = mock.Mock()
-        sampler.should_sample = False
+        sampler.should_sample.return_value = False
         span_context = mock.Mock()
         tracer = request_tracer.RequestTracer(
             sampler=sampler,
@@ -189,7 +189,7 @@ def test_end_span_not_sampled(self):
 
     def test_end_span_sampled(self):
         sampler = mock.Mock()
-        sampler.should_sample = True
+        sampler.should_sample.return_value = True
         tracer = request_tracer.RequestTracer(sampler=sampler)
         span = mock.Mock()
         tracer.tracer._span_stack.append(span)
@@ -201,7 +201,7 @@ def test_current_span_not_sampled(self):
         from opencensus.trace.tracer import base
 
         sampler = mock.Mock()
-        sampler.should_sample = False
+        sampler.should_sample.return_value = False
         tracer = request_tracer.RequestTracer(sampler=sampler)
 
         span = tracer.current_span()
@@ -210,7 +210,7 @@ def test_current_span_not_sampled(self):
 
     def test_current_span_sampled(self):
         sampler = mock.Mock()
-        sampler.should_sample = True
+        sampler.should_sample.return_value = True
         tracer = request_tracer.RequestTracer(sampler=sampler)
         span = mock.Mock()
         tracer.tracer._span_stack.append(span)
@@ -223,7 +223,7 @@ def test_add_label_to_current_span_not_sampled(self):
         from opencensus.trace.tracer import base
 
         sampler = mock.Mock()
-        sampler.should_sample = False
+        sampler.should_sample.return_value = False
         tracer = request_tracer.RequestTracer(sampler=sampler)
         tracer.add_label_to_current_span('key', 'value')