db.checkMetadataConsistency.txt

=============================
db.checkMetadataConsistency()
=============================

.. default-domain:: mongodb

.. contents:: On this page
   :local:
   :backlinks: none
   :depth: 1
   :class: singlecol

Definition
----------

.. method:: db.checkMetadataConsistency(options)

   Performs a series of consistency checks on sharding metadata for the cluster 
   or database.   This method returns a cursor with either all or a batch of
   the inconsistency results found.

   .. |dbcommand| replace:: :dbcommand:`checkMetadataConsistency` command
   .. include:: /includes/fact-mongosh-shell-method-alt.rst

   Run this method after major maintenance operations, such as upgrades and
   downgrades, or to check if the cluster metadata is inconsistent or
   corrupted due to bugs in previous releases of MongoDB.

   .. include:: /includes/inconsistency-type/index-note

   By default, the method checks sharding metadata for the given database.
   If run on the ``admin`` database, it instead checks sharding metadata
   for the entire cluster.

   For more information on the inconsistencies this method searches for,
   see :ref:`inconsistency-types`.

   :returns: This method returns a cursor with a ``documents`` array, 
      which contains a document for each inconsistency found in 
      the sharding metadata.

Compatibility
-------------

This method is available in deployments hosted in the following environments: 

.. include:: /includes/fact-environments-atlas-only.rst

.. include:: /includes/fact-environments-atlas-support-no-free.rst

.. include:: /includes/fact-environments-onprem-only.rst

.. include:: /includes/method/checkMetadataConsistency-execute-mongos.rst

Syntax
-------

The :method:`db.checkMetadataConsistency` method has the following syntax:

.. code-block:: javascript

   db.checkMetadataConsistency( { <options> } )

The ``options`` document can take the following fields and values:

.. include:: /includes/inconsistency-type/checkMetadataConsistency-options.rst

Example
-------

Perform a Consistency Check on the Database
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To perform consistency checks on a database, call the 
``db.checkMetadataConsistency()`` method:

.. io-code-block::

   .. input::
      :language: javascript

      use library
      db.checkMetadataConsistency()

   .. output::
      :language: json

      {
         cursorHasMore: false,
         documents: [
            {
               type: "MisplacedCollection",
               description: "Unsharded collection found on shard different from database primary shard",
               details: {
                  namespace: "library.authors",
                  shard: "shard02",
                  localUUID: new UUID("1ad56770-61e2-48e9-83c6-8ecefe73cfc4")
               }
            }
         ],
      }
 
Perform Consistency Checks on the Cluster
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  

To perform consistency checks on a cluster, call the 
``db.checkMetadataConsistency()`` method from the ``admin`` database:

.. io-code-block::

   .. input::
      :language: javascript

      use admin
      db.checkMetadataConsistency()

   .. output::
      :language: json

      {
         cursorHasMore: false,
         documents: [
            {
               type: "MisplacedCollection",
               description: "Unsharded collection found on shard different from database primary shard",
               details: {
                  namespace: "library.authors",
                  shard: "shard02",
                  localUUID: new UUID("1ad56770-61e2-48e9-83c6-8ecefe73cfc4")
               }
            }
         ],
      }