Prior to MongoDB v8.0, sharding a collection was an irreversible action. Starting in v8.0, you can unshard a collection to the shard of your choice.
When to Unshard a Collection
The following scenarios benefit from moving unsharded collections across shards.
Correcting unintentional sharding of a collection
If you discover that sharding was unnecessary or causing performance issues, you can use the``unshardCollection`` command to rewrite the entire collection as an unsharded collection.
Simplifying zone-based isolation
If you use zones to keep a sharded collection on a single shard, you can now unshard the collection to reduce the complexity in your cluster.
Consolidating previously sharded small collections
If you sharded small collections to efficiently utilize resources on multiple shards, you can unshard and move the collections to a shard of your choice. Doing so reduces the complexity of a deployment while maintaining appropriate resource allocation.
Command Syntax
sh.unshardCollection("database.collection", "shardName")The following example unshards the riders collection in the taxi
database and moves the collection to shard1.
db.adminCommand({unshardCollection:"taxi.riders", toShard: "shard1"})