C100DBA Sharding Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  db.runCommand({enableSharding: "sales"}) on the admin database

  Why it's wrong here

  While the enableSharding command exists, it must be run against the admin database. Running db.runCommand() from a non-admin database will fail. The helper sh.enableSharding() automatically targets the admin database and is the correct method to use from mongos.

• ✗

  sh.addShard("sales")

  Why it's wrong here

  sh.addShard() is used to add a shard (a replica set) to the cluster, not to enable sharding on a database. The argument should be a replica set name and host list, not a database name. Using this command with a database name will result in an error because it expects a shard connection string.

• ✗

  sh.shardCollection("sales", {_id: "hashed"})

  Why it's wrong here

  sh.shardCollection() is used to shard a specific collection, not to enable sharding on a database. It requires the full namespace of the collection, such as "sales.orders". Running it without a collection name will fail. Enabling sharding on the database must be done first with sh.enableSharding().

• ✓

  sh.enableSharding("sales")

  Why this is correct

  The sh.enableSharding() method is the correct command to enable sharding on a specific database. It must be run on mongos and takes the database name as an argument. Once enabled, collections within that database can be sharded using sh.shardCollection(). This is a prerequisite step before sharding any collection in the database.