> For the complete MongoDB documentation index, see www.mongodb.com/docs/llms.txt

# Drop a Hashed Shard Key Index

Starting in MongoDB 7.0.3 (and 6.0.12 and 5.0.22), you can drop the index for a hashed shard key.

This can speed up data insertion for collections sharded with a hashed shard key.

## About this Task

Dropping an [unnecessary index](https://www.mongodb.com/docs/manual/data-modeling/design-antipatterns/unnecessary-indexes.md#std-label-unnecessary-indexes-antipattern) can speed up CRUD operations. Each CRUD operation has to update all the indexes related to a document. Removing one index can increase the speed of all CRUD operations.

**Important:**

You should only drop a hashed shard key index from a collection if a supporting non-hashed index on the shard key exists. If a supporting non-hashed index does not exist on the shard key, queries filtering by the shard key perform a [collection scan](https://www.mongodb.com/docs/manual/reference/glossary.md#std-term-collection-scan). To see what indexes exist on a collection, use [`db.collection.getIndexes()`.](https://www.mongodb.com/docs/manual/reference/method/db.collection.getindexes.md#mongodb-method-db.collection.getIndexes)

## Considerations

When dropping a hashed shard key index, consider the following:

- The server disables balancing for your collection and excludes the collection from future balancing rounds. As a result, if you later add or remove a shard, the server cannot rebalance the collection's data. To include the collection in future balancing rounds, recreate the hashed shard key index.

- When you drop the shard key index, the range deleter does not clean up any remaining orphans in your collection. You must confirm that no orphaned documents exist in your collection before dropping the hashed shard key index. See the below procedure for how to confirm that there are no orphaned documents in your collection.

## Steps

1. Stop the balancer

   Run the following command to stop the balancer:

   ```javascript
   sh.stopBalancer()
   ```

   You can only run `sh.stopBalancer()` on `mongos`. `sh.stopBalancer()` produces an error if run on `mongod`.

2. Confirm there are no orphaned documents in your collection

   Starting in MongoDB 6.0.3, you can run an aggregation using the [`$shardedDataDistribution`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/shardeddatadistribution.md#mongodb-pipeline-pipe.-shardedDataDistribution) stage to confirm no orphaned documents remain:

   ```javascript
   db.aggregate([
      { $shardedDataDistribution: {} },
      { $match: { "ns": "<database>.<collection>" } }
   ])
   ```

   `$shardedDataDistribution` has output similar to the following:

   ```json
   [
     {
       "ns": "test.names",
       "shards": [
         {
           "shardName": "shard-1",
           "numOrphanedDocs": 0,
           "numOwnedDocuments": 6,
           "ownedSizeBytes": 366,
           "orphanedSizeBytes": 0
         },
         {
           "shardName": "shard-2",
           "numOrphanedDocs": 0,
           "numOwnedDocuments": 6,
           "ownedSizeBytes": 366,
           "orphanedSizeBytes": 0
         }
       ]
     }
   ]
   ```

   Ensure that `"numOrphanedDocs"` is `0` for each shard in the cluster.

3. Drop the hashed shard key index

   Run the following command to drop the index:

   ```javascript
   db.collection.dropIndex("<index name>")
   ```

4. Restart the balancer

   Run the following command to restart the balancer on the cluster:

   ```javascript
   sh.startBalancer()
   ```

## Learn More

- [Hashed Sharding](https://www.mongodb.com/docs/manual/core/hashed-sharding.md#std-label-sharding-hashed)

- [Sharded Cluster Balancer](https://www.mongodb.com/docs/manual/core/sharding-balancer-administration.md#std-label-sharding-balancing)

- [`db.collection.dropIndex()`](https://www.mongodb.com/docs/manual/reference/method/db.collection.dropindex.md#mongodb-method-db.collection.dropIndex)

- [`sh.stopBalancer()`](https://www.mongodb.com/docs/manual/reference/method/sh.stopbalancer.md#mongodb-method-sh.stopBalancer)

- [`sh.startBalancer()`](https://www.mongodb.com/docs/manual/reference/method/sh.startbalancer.md#mongodb-method-sh.startBalancer)

- [`sh.getBalancerState()`](https://www.mongodb.com/docs/manual/reference/method/sh.getbalancerstate.md#mongodb-method-sh.getBalancerState)