instr(txnames): Count number of discovered rules (#49085)

In order to detect regressions in our transaction clusterer, keep track
of the number of _new_ rules discovered across projects.

ref: getsentry/team-ingest#124

src/sentry/ingest/transaction_clusterer/rules.py

@@ -83,7 +83,9 @@ def read_sorted(self, project: Project) -> List[Tuple[ReplacementRule, int]]:
         return [tuple(lst) for lst in ret]  # type: ignore[misc]
 
     def read(self, project: Project) -> RuleSet:
-        return {rule: last_seen for rule, last_seen in self.read_sorted(project)}
+        rules = {rule: last_seen for rule, last_seen in self.read_sorted(project)}
+        self.last_read = rules
+        return rules
 
     def _sort(self, rules: RuleSet) -> List[Tuple[ReplacementRule, int]]:
         """Sort rules by number of slashes, i.e. depth of the rule"""
@@ -188,23 +190,33 @@ def get_sorted_rules(project: Project) -> List[Tuple[ReplacementRule, int]]:
     return ProjectOptionRuleStore().read_sorted(project)
 
 
-def update_rules(project: Project, new_rules: Sequence[ReplacementRule]) -> None:
+def update_rules(project: Project, new_rules: Sequence[ReplacementRule]) -> int:
+    """Write newly discovered rules to projection option and redis, and update last_used.
+
+    Return the number of _new_ rules (that were not already present in project option).
+    """
     # Run the updates even if there aren't any new rules, to get all the stores
     # up-to-date.
     # NOTE: keep in mind this function writes to Postgres, so it shouldn't be
     # called often.
 
     last_seen = _now()
     new_rule_set = {rule: last_seen for rule in new_rules}
+    project_option = ProjectOptionRuleStore()
     rule_store = CompositeRuleStore(
         [
             RedisRuleStore(),
-            ProjectOptionRuleStore(),
+            project_option,
             LocalRuleStore(new_rule_set),
         ]
     )
+
     rule_store.merge(project)
 
+    num_rules_added = len(new_rule_set.keys() - project_option.last_read.keys())
+
+    return num_rules_added
+
 
 def bump_last_used(project: Project, pattern: str) -> None:
     """If an entry for `pattern` exists, bump its last_used timestamp in redis.

src/sentry/ingest/transaction_clusterer/tasks.py

@@ -71,7 +71,10 @@ def cluster_projects(projects: Sequence[Project]) -> None:
                 # The Redis store may have more up-to-date last_seen values,
                 # so we must update the stores to bring these values to
                 # project options, even if there aren't any new rules.
-                rules.update_rules(project, new_rules)
+                num_rules_added = rules.update_rules(project, new_rules)
+
+                # Track a global counter of new rules:
+                metrics.incr("txcluster.new_rules_discovered", num_rules_added)
 
                 # Clear transaction names to prevent the set from picking up
                 # noise over a long time range.

tests/sentry/ingest/test_transaction_clusterer.py

@@ -176,12 +176,12 @@ def test_save_rules(default_project):
     assert project_rules == {}
 
     with freeze_time("2012-01-14 12:00:01"):
-        update_rules(project, [ReplacementRule("foo"), ReplacementRule("bar")])
+        assert 2 == update_rules(project, [ReplacementRule("foo"), ReplacementRule("bar")])
     project_rules = get_rules(project)
     assert project_rules == {"foo": 1326542401, "bar": 1326542401}
 
     with freeze_time("2012-01-14 12:00:02"):
-        update_rules(project, [ReplacementRule("bar"), ReplacementRule("zap")])
+        assert 1 == update_rules(project, [ReplacementRule("bar"), ReplacementRule("zap")])
     project_rules = get_rules(project)
     assert {"bar": 1326542402, "foo": 1326542401, "zap": 1326542402}
 
@@ -352,7 +352,7 @@ def test_transaction_clusterer_bumps_rules(_, default_organization):
         assert get_rules(project1) == {"/user/*/**": 1}
         # Update rules to update the project option storage.
         with mock.patch("sentry.ingest.transaction_clusterer.rules._now", lambda: 3):
-            update_rules(project1, [])
+            assert 0 == update_rules(project1, [])
         # After project options are updated, the last_seen should also be updated.
         assert get_redis_rules(project1) == {"/user/*/**": 2}
         assert get_rules(project1) == {"/user/*/**": 2}