Find a Shard Key

MongoDB 5.0 is end of life as of October 2024. This version of the documentation is no longer supported. To upgrade your 5.0 deployment, see the MongoDB 6.0 upgrade procedures.

Every shared collection has a shard key. To display the shard key, connect to a mongos instance and run the db.printShardingStatus() method:

db.printShardingStatus()

The output resembles:

<dbname>.<collection>
   shard key: { <shard key> : <1 or hashed> }
   unique: <boolean>
   balancing: <boolean>
   chunks:
      <shard name1> <number of chunks>
      <shard name2> <number of chunks>
      ...
   { <shard key>: <min range1> } -->> { <shard key> : <max range1> } on : <shard name> <last modified timestamp>
   { <shard key>: <min range2> } -->> { <shard key> : <max range2> } on : <shard name> <last modified timestamp>
   ...
   tag: <tag1>  { <shard key> : <min range1> } -->> { <shard key> : <max range1> }
   ...

For more details on the db.printShardingStatus() output, see the sharded collection section on the sh.status() page.

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Set Missing Shard Key Fields

Troubleshoot Shard Keys