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Sharding

db.checkMetadataConsistency()

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  • Definition
  • Compatibility
  • Syntax
  • Example

Definition

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.

Important

mongosh Method

This page documents a mongosh method. This is not the documentation for database commands or language-specific drivers, such as Node.js.

For the database command, see the checkMetadataConsistency command.

For MongoDB API drivers, refer to the language-specific MongoDB driver documentation.

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.

By default, the method does not check indexes for consistency across the shards. Index checks can return false positive inconsistencies if they run concurrent with operations that create, delete, or modify indexes. To check indexes with this method, set the checkIndexes option.

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 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:

  • MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud

Note

This command is supported in all MongoDB Atlas clusters. For information on all commands, see Unsupported Commands.

Syntax

The db.checkMetadataConsistency() method has the following syntax:

db.checkMetadataConsistency( { <options> } )

The options document can take the following fields and values:

Field
Type
Description
checkIndexes
boolean

Sets whether the command also checks indexes in sharding metadata.

By default, this operation is disabled, because if it can return false positives inconsistencies when run concurrent with operations that create, delete, or modify indexes. Only check indexes at times when you know these operations are unlikely to occur.

cursor
document
Configures the return cursor.
cursor.batchSize
integer
Maximum number of sharding metadata inconsistency documents to include in each batch.

Example

Perform a Consistency Check on the Database

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

use library
db.checkMetadataConsistency()
{
   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:

use admin
db.checkMetadataConsistency()
{
   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")
         }
      }
   ],
}

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