Merge lp:~lucio.torre/txstatsd/fix-exp-overflow into lp:txstatsd

[Lucio Torre]

fix exp overflow

we now rescale before processing the metric, to make sure the scale difference between the last scale an now is smaller than RESCALE THRESHOLD.

[lp:~lucio.torre/txstatsd/fix-exp-overflow]

76. By Lucio Torre on 2012-03-07

fix overflow

[Sidnei da Silva (sidnei)]

Looks good.

review: Approve

=== modified file 'txstatsd/stats/exponentiallydecayingsample.py'
--- txstatsd/stats/exponentiallydecayingsample.py	2012-01-30 20:36:02 +0000
+++ txstatsd/stats/exponentiallydecayingsample.py	2012-03-07 20:30:23 +0000
@@ -60,6 +60,11 @@
         @param timestamp: The epoch timestamp of *value* in seconds.
         """
 
+        now = self._wall_time()
+        next = self.next_scale_time
+        if now >= next:
+            self.rescale(now, next)
+
         if timestamp is None:
             timestamp = self.tick()
 
@@ -75,11 +80,6 @@
                 bisect.insort(self._values, (priority, value))
                 self._values = self._values[1:]
 
-        now = self._wall_time()
-        next = self.next_scale_time
-        if now >= next:
-            self.rescale(now, next)
-
     def get_values(self):
         return [v for (k, v) in self._values]
 

=== modified file 'txstatsd/tests/stats/test_exponentiallydecayingsample.py'
--- txstatsd/tests/stats/test_exponentiallydecayingsample.py	2012-02-07 21:11:42 +0000
+++ txstatsd/tests/stats/test_exponentiallydecayingsample.py	2012-03-07 20:30:23 +0000
@@ -67,3 +67,18 @@
                          'Should have 100 elements')
     test_ewma_sample_load.skip = "takes too long to run"
 
+    def test_ewma_overflow(self):
+        """Long pauses on metric input should not overflow weight."""
+        _time = [10000]
+
+        def wtime():
+            return _time[0]
+
+        sample = ExponentiallyDecayingSample(100, 0.99, wall_time=wtime)
+        for i in xrange(100):
+            sample.update(random.normalvariate(0, 10))
+            _time[0] += 10000
+
+        self.assertEqual(sample.size(), 100)
+        self.assertEqual(len(sample.get_values()), 100,
+                         'Should have 100 elements')