AAP-87549 — Add management command to create JobHostSummary composite index (#16586)

Adds `create_host_summary_index` management command that creates the
composite index (host_id, id DESC) on main_jobhostsummary using
CREATE INDEX CONCURRENTLY.

The command is idempotent: it checks for existing valid/invalid indexes,
drops invalid indexes from failed prior attempts, and skips if the index
already exists. Disables statement_timeout for the session to avoid
killing the index build on large tables where ALTER ROLE timeout is set.

Forward-port of tower#7893 (stable-2.6).

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

awx/main/management/commands/create_host_summary_index.py

@@ -0,0 +1,59 @@
+from django.core.management.base import BaseCommand
+from django.db import connection
+
+
+class Command(BaseCommand):
+    help = 'Creates composite index (host_id, id DESC) on main_jobhostsummary to improve host list query performance.'
+
+    INDEX_NAME = 'main_jobhostsumm_host_id_desc'
+    TABLE_NAME = 'main_jobhostsummary'
+
+    def _index_status(self):
+        """Check whether the index exists in pg_class and whether it is valid.
+
+        Returns:
+            'valid'   - index exists and is usable; no action needed.
+            'invalid' - index exists but was left in an invalid state by a
+                        previous failed CREATE INDEX CONCURRENTLY; must be
+                        dropped before retrying.
+            None      - index does not exist; safe to create.
+        """
+        with connection.cursor() as cursor:
+            cursor.execute(
+                "SELECT pg_index.indisvalid " "FROM pg_class JOIN pg_index ON pg_class.oid = pg_index.indexrelid " "WHERE pg_class.relname = %s",
+                [self.INDEX_NAME],
+            )
+            row = cursor.fetchone()
+            if row is None:
+                return None
+            return 'valid' if row[0] else 'invalid'
+
+    def handle(self, *args, **options):
+        status = self._index_status()
+
+        if status == 'valid':
+            self.stdout.write(f"Index {self.INDEX_NAME} already exists, nothing to do.")
+            return
+
+        if status == 'invalid':
+            self.stdout.write(f"Dropping invalid index {self.INDEX_NAME} from a previous failed attempt...")
+            with connection.cursor() as cursor:
+                cursor.execute(f"DROP INDEX IF EXISTS {self.INDEX_NAME}")
+
+        self.stdout.write(f"Creating index {self.INDEX_NAME} on {self.TABLE_NAME} (host_id, id DESC) concurrently...")
+
+        # CREATE INDEX CONCURRENTLY cannot run inside a transaction.
+        connection.ensure_connection()
+        old_autocommit = connection.connection.autocommit
+        connection.connection.autocommit = True
+        try:
+            with connection.cursor() as cursor:
+                # Disable statement_timeout for this session — the customer may
+                # have set ALTER ROLE ... SET statement_timeout which would kill
+                # the index build on large tables.
+                cursor.execute("SET statement_timeout = 0")
+                cursor.execute(f"CREATE INDEX CONCURRENTLY {self.INDEX_NAME} " f"ON {self.TABLE_NAME} (host_id, id DESC)")
+        finally:
+            connection.connection.autocommit = old_autocommit
+
+        self.stdout.write(f"Index {self.INDEX_NAME} created successfully.")