pgroonga: Remove unnecessary code from first migration.

This avoids doing a bunch of extra work, including a downtime-risky
`CREATE INDEX` without CONCURRENTLY, when migrating a modern Zulip
system to PGroonga the first time.

pgroonga/migrations/0001_enable.py

@@ -11,43 +11,11 @@ class Migration(migrations.Migration):
     database_setting = settings.DATABASES["default"]
 
     operations = [
+        # This previously had additional operations, but they are all
+        # undone in migration 0003 because we switched to using the
+        # PGroonga v2 API.
         migrations.RunSQL(
-            [
+            sql="ALTER TABLE zerver_message ADD COLUMN search_pgroonga text;",
-                (
+            reverse_sql="ALTER TABLE zerver_message DROP COLUMN search_pgroonga;",
-                    """
-DO $$BEGIN
-EXECUTE format('ALTER ROLE %%I SET search_path TO %%L,public,pgroonga,pg_catalog', %(USER)s, %(SCHEMA)s);
-
-SET search_path = %(SCHEMA)s,public,pgroonga,pg_catalog;
-
-ALTER TABLE zerver_message ADD COLUMN search_pgroonga text;
-
--- TODO: We want to use CREATE INDEX CONCURRENTLY but it can't be used in
--- transaction. Django uses transaction implicitly.
--- Django 1.10 may solve the problem.
-CREATE INDEX zerver_message_search_pgroonga ON zerver_message
-  USING pgroonga(search_pgroonga pgroonga.text_full_text_search_ops);
-END$$
-""",
-                    database_setting,
-                )
-            ],
-            [
-                (
-                    """
-DO $$BEGIN
-SET search_path = %(SCHEMA)s,public,pgroonga,pg_catalog;
-
-DROP INDEX zerver_message_search_pgroonga;
-ALTER TABLE zerver_message DROP COLUMN search_pgroonga;
-
-SET search_path = %(SCHEMA)s,public;
-
-EXECUTE format('ALTER ROLE %%I SET search_path TO %%L,public', %(USER)s, %(SCHEMA)s);
-END$$
-""",
-                    database_setting,
-                )
-            ],
         ),
     ]

pgroonga/migrations/0003_v2_api_upgrade.py

@@ -11,6 +11,16 @@ class Migration(migrations.Migration):
 
     database_setting = settings.DATABASES["default"]
     operations = [
+        # This migration does the following things:
+        # * Undoes the `search_path` changes from the original migration 0001,
+        #   which are no longer necessary with the modern PGroonga API.
+        #   (Note that we've deleted those changes from the current version of the
+        #    0001 migration).
+        # * Drops a legacy-format v1 index if present (will be only if upgrading
+        #   an old server).
+        # * Does a CREATE INDEX CONCURRENTLY to add a PGroonga v2 search index
+        #   on the message.search_pgroonga column (which was populated in
+        #   migration 0002).
         migrations.RunSQL(
             [
                 (
@@ -20,7 +30,7 @@ EXECUTE format('ALTER ROLE %%I SET search_path TO %%L,public', %(USER)s, %(SCHEM
 
 SET search_path = %(SCHEMA)s,public;
 
-DROP INDEX zerver_message_search_pgroonga;
+DROP INDEX IF EXISTS zerver_message_search_pgroonga;
 END$$
 """,
                     database_setting,
@@ -39,7 +49,7 @@ EXECUTE format('ALTER ROLE %%I SET search_path TO %%L,public,pgroonga,pg_catalog
 
 SET search_path = %(SCHEMA)s,public,pgroonga,pg_catalog;
 
-DROP INDEX zerver_message_search_pgroonga;
+DROP INDEX IF EXISTS zerver_message_search_pgroonga;
 END$$
 """,
                     database_setting,