add composite index on events table

src/google/adk/sessions/schemas/v1.py

@@ -28,8 +28,10 @@
 from typing import Any
 
 from google.adk.platform import uuid as platform_uuid
+from sqlalchemy import desc
 from sqlalchemy import ForeignKeyConstraint
 from sqlalchemy import func
+from sqlalchemy import Index
 from sqlalchemy import inspect
 from sqlalchemy.ext.mutable import MutableDict
 from sqlalchemy.orm import DeclarativeBase
@@ -187,6 +189,13 @@ class StorageEvent(Base):
           ["sessions.app_name", "sessions.user_id", "sessions.id"],
           ondelete="CASCADE",
       ),
+      Index(
+          "idx_events_app_user_session_ts",
+          "app_name",
+          "user_id",
+          "session_id",
+          desc("timestamp"),
+      ),
   )
 
   @classmethod

tests/unittests/sessions/migration/test_database_schema.py

@@ -72,6 +72,13 @@ def get_schema_version(sync_conn):
     event_col_names = {c['name'] for c in event_cols}
     assert 'event_data' in event_col_names
     assert 'actions' not in event_col_names
+
+    # Verify composite index on events table
+    event_indexes = await conn.run_sync(
+        lambda sync_conn: inspect(sync_conn).get_indexes('events')
+    )
+    idx_names = {idx['name'] for idx in event_indexes}
+    assert 'idx_events_app_user_session_ts' in idx_names
   await engine.dispose()