Add user created_at index (#4392)

* Add user created_at index

* lint

discovery-provider/alembic/versions/1eec1d124caf_create_index_on_users_created_at.py

@@ -0,0 +1,33 @@
+"""create index on users created_at
+
+Revision ID: 1eec1d124caf
+Revises: 959f15b94094
+Create Date: 2022-11-23 00:01:06.643480
+
+"""
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = '1eec1d124caf'
+down_revision = '959f15b94094'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    conn = op.get_bind()
+    conn.execute(
+        """
+        CREATE INDEX IF NOT EXISTS user_created_at_idx ON users (created_at, user_id) WHERE is_current;
+        """
+    )
+
+
+def downgrade():
+    conn = op.get_bind()
+    conn.execute(
+        """
+        DROP INDEX IF EXISTS user_created_at_idx;
+        """
+    )