[Monitoring] Fix untriaged testcase age oversampling, add untriaged testcase count (#4494)

### Motivation

#4364 implemented a metric to track the percentile distributions of
untriaged testcase age. It was overcounting testcases:
* Testcases for which a bug was already filed
* Testcases for which the crash was unimportant

This PR solves this issue, and adds the UNTRIAGED_TESTCASE_COUNT metric,
drilled down by job and platform, so we can also know how many testcases
are stuck, and not only their age distribution.

Author: vitorguidi

src/clusterfuzz/_internal/cron/triage.py

@@ -309,14 +309,22 @@ def _file_issue(testcase, issue_tracker, throttler):
   return filed
 
 
-def _emit_untriaged_testcase_age_metric(critical_tasks_completed: bool,
-                                        testcase: data_types.Testcase):
+untriaged_testcase_count = {}
+
+
+def _increment_untriaged_testcase_count(testcase: data_types.Testcase):
+  identifier = (testcase.job_type, testcase.platform)
+  if identifier not in untriaged_testcase_count:
+    untriaged_testcase_count[identifier] = 0
+  untriaged_testcase_count[identifier] += 1
+
+
+def _emit_untriaged_testcase_age_metric(testcase: data_types.Testcase):
   """Emmits a metric to track age of untriaged testcases."""
-  if critical_tasks_completed:
-    return
   if not testcase.timestamp:
     return
 
+  _increment_untriaged_testcase_count(testcase)
   logs.info(f'Emiting UNTRIAGED_TESTCASE_AGE for testcase {testcase.key.id()} '
             f'(age = {testcase.get_age_in_seconds()})')
   monitoring_metrics.UNTRIAGED_TESTCASE_AGE.add(
@@ -327,6 +335,16 @@ def _emit_untriaged_testcase_age_metric(critical_tasks_completed: bool,
       })
 
 
+def _emit_untriaged_testcase_count_metric():
+  for (job, platform) in untriaged_testcase_count:
+    monitoring_metrics.UNTRIAGED_TESTCASE_COUNT.set(
+        untriaged_testcase_count[(job, platform)],
+        labels={
+            'job': job,
+            'platform': platform,
+        })
+
+
 def main():
   """Files bugs."""
   try:
@@ -373,12 +391,10 @@ def main():
                 f' exclusion list ({testcase.job_type})')
       continue
 
-    # Emmit the metric for testcases that should be triaged.
-    _emit_untriaged_testcase_age_metric(critical_tasks_completed, testcase)
-
     # Skip if we are running progression task at this time.
     if testcase.get_metadata('progression_pending'):
       logs.info(f'Skipping testcase {testcase_id}, progression pending')
+      _emit_untriaged_testcase_age_metric(testcase)
       continue
 
     # If the testcase has a bug filed already, no triage is needed.
@@ -397,6 +413,7 @@ def main():
     # Require that all tasks like minimizaton, regression testing, etc have
     # finished.
     if not critical_tasks_completed:
+      _emit_untriaged_testcase_age_metric(testcase)
       logs.info(
           f'Skipping testcase {testcase_id}, critical tasks still pending.')
       continue
@@ -413,11 +430,13 @@ def main():
     # metadata works well.
     if not testcase.group_id and not dates.time_has_expired(
         testcase.timestamp, hours=data_types.MIN_ELAPSED_TIME_SINCE_REPORT):
+      _emit_untriaged_testcase_age_metric(testcase)
       logs.info(f'Skipping testcase {testcase_id}, pending grouping.')
       continue
 
     if not testcase.get_metadata('ran_grouper'):
       # Testcase should be considered by the grouper first before filing.
+      _emit_untriaged_testcase_age_metric(testcase)
       logs.info(f'Skipping testcase {testcase_id}, pending grouping.')
       continue
 
@@ -447,6 +466,7 @@ def main():
     # File the bug first and then create filed bug metadata.
     if not _file_issue(testcase, issue_tracker, throttler):
       logs.info(f'Issue filing failed for testcase id {testcase_id}')
+      _emit_untriaged_testcase_age_metric(testcase)
       continue
 
     _create_filed_bug_metadata(testcase)
@@ -455,6 +475,8 @@ def main():
     logs.info('Filed new issue %s for testcase %d.' % (testcase.bug_information,
                                                        testcase_id))
 
+  _emit_untriaged_testcase_count_metric()
+
   logs.info('Triage testcases succeeded.')
   return True
 

src/clusterfuzz/_internal/metrics/monitoring_metrics.py

@@ -365,6 +365,16 @@
         monitor.StringField('platform'),
     ])
 
+UNTRIAGED_TESTCASE_COUNT = monitor.GaugeMetric(
+    'issues/untriaged_testcase_count',
+    description='Number of testcases that were not yet triaged '
+    '(have not yet completed analyze, regression,'
+    ' minimization, impact task), in hours.',
+    field_spec=[
+        monitor.StringField('job'),
+        monitor.StringField('platform'),
+    ])
+
 ANALYZE_TASK_REPRODUCIBILITY = monitor.CounterMetric(
     'task/analyze/reproducibility',
     description='Outcome count for analyze task.',