feat(metric_alerts): Backfill new AlertRule level fields (#19555)

This backfills the `AlertRule.resolve_threshold` and `AlertRule.threshold_type` fields. We get the
`threshold_type` from either trigger, since it will always be the same. For `resolve_threshold`, we
choose the min or max depending on whether the rule triggers on above or below thresholds.

migrations_lockfile.txt

@@ -10,7 +10,7 @@ auth: 0008_alter_user_username_max_length
 contenttypes: 0002_remove_content_type_name
 jira_ac: 0001_initial
 nodestore: 0001_initial
-sentry: 0088_rule_level_resolve_threshold_type
+sentry: 0089_rule_level_fields_backfill
 sessions: 0001_initial
 sites: 0002_alter_domain_unique
 social_auth: 0001_initial

src/sentry/migrations/0089_rule_level_fields_backfill.py

@@ -0,0 +1,59 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.29 on 2020-06-25 20:24
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+from sentry.utils.query import RangeQuerySetWrapperWithProgressBar
+
+
+def backfill_rule_level_fields(apps, schema_editor):
+    AlertRule = apps.get_model("sentry", "AlertRule")
+    for alert_rule in RangeQuerySetWrapperWithProgressBar(AlertRule.objects_with_snapshots.all()):
+        triggers = list(alert_rule.alertruletrigger_set.all())
+        # Determine the resolve_threshold and threshold_type from the rule's triggers
+        if triggers:
+            # Threshold types are the same for all triggers on a rule, so just grab one
+            threshold_type = triggers[0].threshold_type
+            resolve_thresholds = [
+                t.resolve_threshold for t in triggers if t.resolve_threshold is not None
+            ]
+            if resolve_thresholds:
+                # Either grab the min or max resolve threshold depending on whether
+                # we're an above or below threshold rule.
+                func = min if threshold_type == 0 else max
+                resolve_threshold = func(resolve_thresholds)
+            else:
+                resolve_threshold = None
+
+            alert_rule.resolve_threshold = resolve_threshold
+            alert_rule.threshold_type = threshold_type
+        else:
+            # Just a failsafe in case we have any bad rules without triggers.
+            alert_rule.threshold_type = 0
+        alert_rule.save()
+
+
+class Migration(migrations.Migration):
+    # This flag is used to mark that a migration shouldn't be automatically run in
+    # production. We set this to True for operations that we think are risky and want
+    # someone from ops to run manually and monitor.
+    # General advice is that if in doubt, mark your migration as `is_dangerous`.
+    # Some things you should always mark as dangerous:
+    # - Large data migrations. Typically we want these to be run manually by ops so that
+    #   they can be monitored. Since data migrations will now hold a transaction open
+    #   this is even more important.
+    # - Adding columns to highly active tables, even ones that are NULL.
+    is_dangerous = False
+
+    # This flag is used to decide whether to run this migration in a transaction or not.
+    # By default we prefer to run in a transaction, but for migrations where you want
+    # to `CREATE INDEX CONCURRENTLY` this needs to be set to False. Typically you'll
+    # want to create an index concurrently when adding one to an existing table.
+    atomic = False
+
+    dependencies = [("sentry", "0088_rule_level_resolve_threshold_type")]
+
+    operations = [
+        migrations.RunPython(backfill_rule_level_fields, reverse_code=migrations.RunPython.noop)
+    ]