Missed a "concurrently"! Added comments.

corehq/motech/repeaters/migrations/0015_alter_repeatrecord_state_and_more.py

@@ -1,6 +1,8 @@
 """
 Adds an index for RepeatRecord.state and a partial index for
-next_attempt_at + not_paused
+next_attempt_at + not_paused. The indexes are used by
+RepeaterManager.all_ready() to select all Repeaters that have
+RepeatRecords that are ready to be sent.
 """
 from django.db import migrations
 
@@ -13,23 +15,10 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
-        # migrations.AlterField(
-        #     model_name="repeatrecord",
-        #     name="state",
-        #     field=models.PositiveSmallIntegerField(
-        #         choices=[
-        #             (1, "Pending"),
-        #             (2, "Failed"),
-        #             (4, "Succeeded"),
-        #             (8, "Cancelled"),
-        #             (16, "Empty"),
-        #             (32, "Invalid Payload"),
-        #         ],
-        #         db_index=True,
-        #         default=1,
-        #     ),
-        # ),
-        # Equivalent to the migration above, but builds the index concurrently
+        # Adds an index for RepeatRecord.state. Builds it concurrently.
+        # The SQL and the index name were determined from the generated
+        # Django migration. The migration was made concurrent by setting
+        # `atomic = False` and adding "CONCURRENTLY" to the SQL.
         migrations.RunSQL(
             sql="""
             CREATE INDEX CONCURRENTLY "repeaters_repeatrecord_state_8055083b"
@@ -40,17 +29,13 @@ class Migration(migrations.Migration):
             """
         ),
 
-        # migrations.AddIndex(
-        #     model_name="repeater",
-        #     index=models.Index(
-        #         condition=models.Q(("is_paused", False)),
-        #         fields=["next_attempt_at"],
-        #         name="next_attempt_at_not_paused_idx",
-        #     ),
-        # ),
+        # Adds an index for Repeater.next_attempt_at when
+        # Repeater.is_paused is False. Builds it concurrently.
         migrations.RunSQL(
             sql="""
-            CREATE INDEX "next_attempt_at_not_paused_idx" ON "repeaters_repeater" ("next_attempt_at") WHERE NOT "is_paused";
+            CREATE INDEX CONCURRENTLY "next_attempt_at_not_paused_idx"
+            ON "repeaters_repeater" ("next_attempt_at")
+            WHERE NOT "is_paused";
             """,
             reverse_sql="""
             DROP INDEX CONCURRENTLY "next_attempt_at_not_paused_idx";