Add logs in consistent_restore_mesh to examine the invariant.

PiperOrigin-RevId: 703218403

checkpoint/orbax/checkpoint/experimental/emergency/multihost.py

@@ -132,11 +132,34 @@ def consistent_restore_mesh(
   """
   # Map how device ids changed across restarts.
   device_id_across_restarts = {}
-  for i in range(len(previous_distributed_to_device_ids)):
-    for j in range(len(previous_distributed_to_device_ids[i])):
-      previous_id = previous_distributed_to_device_ids[i][j]
-      current_id = current_distributed_to_device_ids[i][j]
+  assert len(previous_distributed_to_device_ids) == len(
+      current_distributed_to_device_ids
+  )
+
+  logging.debug(
+      'previous_distributed_to_device_ids: %s',
+      previous_distributed_to_device_ids,
+  )
+  logging.debug(
+      'current_distributed_to_device_ids: %s',
+      current_distributed_to_device_ids,
+  )
+  # TODO(b/376748289): remove the following variables after bug is fixed.
+  previous_device_to_distributed_id = {}
+  current_device_to_distributed_id = {}
+  for distributed_id in range(len(previous_distributed_to_device_ids)):
+    logging.debug(
+        'distributed_id: %s, previous_device_ids: %s, current_device_ids: %s',
+        distributed_id,
+        previous_distributed_to_device_ids[distributed_id],
+        current_distributed_to_device_ids[distributed_id],
+    )
+    for j in range(len(previous_distributed_to_device_ids[distributed_id])):
+      previous_id = previous_distributed_to_device_ids[distributed_id][j]
+      current_id = current_distributed_to_device_ids[distributed_id][j]
       device_id_across_restarts[previous_id] = current_id
+      previous_device_to_distributed_id[previous_id] = distributed_id
+      current_device_to_distributed_id[current_id] = distributed_id
   logging.debug(
       'device_id_across_restarts (key: previous_id, value: current_id): %s',
       device_id_across_restarts,
@@ -150,6 +173,28 @@ def consistent_restore_mesh(
       jax_devices_by_id[device_id_across_restarts[id]]
       for id in previous_flattened_mesh_device_ids
   ]
+  logging.debug(
+      'previous_flattened_mesh_device_ids: %s',
+      previous_flattened_mesh_device_ids,
+  )
+  new_flattened_mesh_device_ids = [d.id for d in new_flattened_mesh_devices]
+  logging.debug(
+      'new_flattened_mesh_device_ids: %s',
+      new_flattened_mesh_device_ids,
+  )
+
+  previous_flattened_distributed_ids = [
+      previous_device_to_distributed_id[id]
+      for id in previous_flattened_mesh_device_ids
+  ]
+  current_flattened_distributed_ids = [
+      current_device_to_distributed_id[id]
+      for id in new_flattened_mesh_device_ids
+  ]
+  # The following is the invariant considering the distributed ids are
+  # the same across restarts.
+  assert previous_flattened_distributed_ids == current_flattened_distributed_ids
+
   new_mesh_devices = np.array(new_flattened_mesh_devices).reshape(
       user_mesh.devices.shape
   )