perf: don't fetch from db in constructor

shared/rollouts/__init__.py

@@ -93,9 +93,7 @@ def __init__(self, name, proportion=None, salt=None):
             args["salt"] = salt
 
         # so it is hashable
-        args = tuple(sorted(args.items()))
-
-        self._fetch_and_set_from_db(args)
+        self.args = tuple(sorted(args.items()))
 
     def check_value(self, identifier, default=False):
         """
@@ -104,7 +102,12 @@ def check_value(self, identifier, default=False):
         feature variants via Django Admin.
         """
         # Will only run and refresh values from the database every ~5 minutes due to TTL cache
-        self._fetch_and_set_from_db()
+        self._fetch_and_set_from_db(self.args)
+
+        if (
+            self.args
+        ):  # to create a default when `check_value()` is run for the first time
+            self.args = None
 
         return self._check_value(identifier, default)
 

tests/unit/test_rollouts.py

@@ -24,10 +24,13 @@ def test_buckets(self):
             "complex",
             0.5,
         )
+
         # # To make the math simpler, let's pretend our hash function can only
         # # return 200 different values.
         with patch.object(Feature, "HASHSPACE", 200):
 
+            complex_feature.check_value("garbage")  # to force fetch values from db
+
             # Because the top-level feature proportion is 0.5, we are only using the
             # first 50% of our 200 hash values as our test population: [0..100]
             # Each feature variant has a proportion of 1/3, so our three buckets