Introduction to MongoDB collection.getShardVersion() Method

The getShardVersion() method is a method in MongoDB used to retrieve shard version information. It can be used to determine which replica is the latest in a specific document in a sharded cluster.

Syntax

The syntax of the getShardVersion() method is as follows:

db.collection.getShardVersion()

Here, db.collection specifies the collection to query.

Use Case

In a MongoDB sharded cluster, to ensure consistency of data, version synchronization is required among the various shards. When a node updates data, other nodes need to be notified to update the version number. Therefore, the getShardVersion() method can be used to query version information for a specific document and determine which node has the latest version.

Example

The following example demonstrates how to use the getShardVersion() method to retrieve version information for a specific document in a collection.

Assume we have a collection named students, which contains the following documents:

{ "_id" : 1, "name" : "Alice", "age" : 20 }
{ "_id" : 2, "name" : "Bob", "age" : 22 }
{ "_id" : 3, "name" : "Charlie", "age" : 25 }

We can use the getShardVersion() method to retrieve version information for the document with _id equal to 1, as follows:

db.students.getShardVersion({ _id: 1 })

After executing the above command, the following result will be returned:

{
  "uuid": BinData(3, "xxx"),
  "timestamp": Timestamp(1646748622, 1),
  "configsvrConnectionString": "",
  "lastMod": Timestamp(1646748622, 1),
  "minCompatibleVersion": 5,
  "readOnly": false,
  "majorityReadable": true,
  "msg": "isdbgrid",
  "version": 2
}

Here, uuid is the unique identifier of the cluster, timestamp is the timestamp of the version number, lastMod is the last modification time of the document, and version is the version number.

Conclusion

The getShardVersion() method is a method in MongoDB sharded cluster used to retrieve version information for a specific document. By querying version information, it is possible to determine which node has the latest version, ensuring data consistency.