Question: How can you check if sharding is enabled in MongoDB?

Answer

To check if sharding is enabled in MongoDB, you can follow these steps that involve using the MongoDB shell (mongo). This provides an interface for interacting with your MongoDB deployment. The primary focus will be on querying MongoDB's configuration to ascertain the sharding status.

1. Connect to the MongoDB Shell: First, ensure you're connected to your MongoDB instance by running the mongo command.

```shell
mongo
```

2. Use the admin Database: Sharding information is maintained globally across the cluster in the admin database. Switch to the admin database:

```javascript
use admin
```

3. Check for Sharding Status: To determine if sharding is enabled and obtain details about the sharded cluster, run the listShards command. It returns information about all shards in the cluster.

```javascript
db.adminCommand({ listShards: 1 })
```

If sharding is enabled, this command will return a list of the shards along with their respective details. If sharding is not enabled or there are no shards defined, you'll likely receive an empty list or an error message indicating that the cluster is not a sharded cluster.

4. Alternative Method - Checking the Config Database: Another approach involves checking the config database, which contains metadata regarding the sharded cluster. Specifically, the databases collection in the config database can provide insight into which databases are sharded.

```javascript
use config
db.databases.find()
```

In the output, look for a field named partitioned. If it's set to true for any database, then sharding is enabled for that database.

5. Reviewing Collections for Sharding: To drill down further, you can check individual collections within a database to see if they're sharded:

```javascript
use yourDatabaseName
db.printShardingStatus()
```

Replace yourDatabaseName with the name of your database. This command prints the sharding status of the collections within the specified database. For sharded collections, you will see the shard key and the distribution of data across shards.

In summary, by utilizing the MongoDB shell commands such as listShards, inspecting the config database, and examining specific databases and collections with printShardingStatus(), you can effectively determine whether sharding is enabled in your MongoDB deployment.