migrations: Subscription.is_user_active denormalization - step two.

This adds a migration to do the backfill and add the index that'll be
used to optimize the bulk_get_subscriber_user_ids query in the next
commit.

zerver/migrations/0313_finish_is_user_active_migration.py

@@ -0,0 +1,59 @@
+# Generated by Django 3.1.5 on 2021-02-07 14:56
+
+from django.contrib.postgres.operations import AddIndexConcurrently
+from django.db import connection, migrations, models
+from django.db.backends.postgresql.schema import DatabaseSchemaEditor
+from django.db.migrations.state import StateApps
+
+
+def backfill_is_user_active(apps: StateApps, schema_editor: DatabaseSchemaEditor) -> None:
+    Subscription = apps.get_model("zerver", "Subscription")
+    BATCH_SIZE = 1000
+    lower_id_bound = 0
+
+    max_id = Subscription.objects.aggregate(models.Max("id"))["id__max"]
+    if max_id is None:
+        # No Subscription entries
+        return
+    while lower_id_bound <= max_id:
+        print(f"Processed {lower_id_bound} / {max_id}")
+        upper_id_bound = lower_id_bound + BATCH_SIZE
+        with connection.cursor() as cursor:
+            cursor.execute(
+                """
+                UPDATE zerver_subscription
+                SET is_user_active = zerver_userprofile.is_active
+                FROM zerver_userprofile
+                WHERE zerver_subscription.user_profile_id = zerver_userprofile.id
+                AND zerver_subscription.id BETWEEN %(lower_id_bound)s AND %(upper_id_bound)s
+                """,
+                {"lower_id_bound": lower_id_bound, "upper_id_bound": upper_id_bound},
+            )
+
+        lower_id_bound += BATCH_SIZE + 1
+
+
+class Migration(migrations.Migration):
+    atomic = False
+
+    dependencies = [
+        ("zerver", "0312_subscription_is_user_active"),
+    ]
+
+    operations = [
+        migrations.RunPython(backfill_is_user_active, reverse_code=migrations.RunPython.noop),
+        # Make the field non-null now that we backfilled.
+        migrations.AlterField(
+            model_name="subscription",
+            name="is_user_active",
+            field=models.BooleanField(),
+        ),
+        AddIndexConcurrently(
+            model_name="subscription",
+            index=models.Index(
+                condition=models.Q(("active", True), ("is_user_active", True)),
+                fields=["recipient", "user_profile"],
+                name="zerver_subscription_recipient_id_user_profile_id_idx",
+            ),
+        ),
+    ]

zerver/models.py

@@ -2570,7 +2570,7 @@ class Subscription(models.Model):
     # We intentionally don't specify a default value to promote thinking
     # about this explicitly, as in some special cases, such as data import,
     # we may be creating Subscription objects for a user that's deactivated.
-    is_user_active: Optional[bool] = models.BooleanField(null=True)
+    is_user_active: bool = models.BooleanField()
 
     ROLE_STREAM_ADMINISTRATOR = 20
     ROLE_MEMBER = 50
@@ -2600,6 +2600,13 @@ class Subscription(models.Model):
 
     class Meta:
         unique_together = ("user_profile", "recipient")
+        indexes = [
+            models.Index(
+                fields=("recipient", "user_profile"),
+                name="zerver_subscription_recipient_id_user_profile_id_idx",
+                condition=Q(active=True, is_user_active=True),
+            ),
+        ]
 
     def __str__(self) -> str:
         return f"<Subscription: {self.user_profile} -> {self.recipient}>"