Resolve migration conflict, add comments

corehq/motech/repeaters/migrations/0014_repeater_max_workers.py → corehq/motech/repeaters/migrations/0015_repeater_max_workers.py

@@ -4,7 +4,7 @@
 class Migration(migrations.Migration):
 
     dependencies = [
-        ("repeaters", "0013_alter_repeatrecord_state_and_more"),
+        ("repeaters", "0014_alter_repeater_request_method"),
     ]
 
     operations = [

corehq/motech/repeaters/migrations/0016_add_indexes.py

@@ -0,0 +1,44 @@
+"""
+Adds an index for RepeatRecord.state and a partial index for
+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
+
+
+class Migration(migrations.Migration):
+    atomic = False
+
+    dependencies = [
+        ("repeaters", "0015_repeater_max_workers"),
+    ]
+
+    operations = [
+        # 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"
+            ON "repeaters_repeatrecord" ("state");
+            """,
+            reverse_sql="""
+            DROP INDEX CONCURRENTLY "repeaters_repeatrecord_state_8055083b";
+            """
+        ),
+
+        # Adds an index for Repeater.next_attempt_at when
+        # Repeater.is_paused is False. Builds it concurrently.
+        migrations.RunSQL(
+            sql="""
+            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";
+            """
+        )
+    ]

migrations.lock

@@ -837,6 +837,8 @@ repeaters
  0012_formexpressionrepeater_arcgisformexpressionrepeater
  0013_alter_repeatrecord_state_and_more
  0014_alter_repeater_request_method
+ 0015_repeater_max_workers
+ 0016_add_indexes
 reports
  0001_initial
  0002_auto_20171121_1803