60 mongodb runtime_error ai_generated partial

MongoServerError: chunk split failed: could not find the shard key value for document

ID: mongodb/sharded-collection-chunk-split-error

Also available as: JSON · Markdown · 中文
78%Fix Rate
83%Confidence
1Evidence
2023-11-12First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
mongodb-4.2 active — — —
mongodb-4.4 active — — —
mongodb-5.0 active — — —
mongodb-6.0 active — — —
mongodb-7.0 active — — —

Root Cause

During chunk migration or splitting, the balancer or mongos cannot determine the shard key value for one or more documents, often due to missing shard key fields or null values.

generic

中文

在块迁移或拆分过程中，均衡器或 mongos 无法确定一个或多个文档的分片键值，通常是由于缺少分片键字段或值为 null。

Official Documentation

https://www.mongodb.com/docs/manual/core/sharding-data-partitioning/

Workarounds

  1. 85% success Find documents with missing or null shard key fields using a query like `db.collection.find({shardKeyField:{$exists:false}})` and update them with a valid value. Example: `db.collection.updateMany({shardKeyField:{$exists:false}},{$set:{shardKeyField:0}})` 
    Find documents with missing or null shard key fields using a query like `db.collection.find({shardKeyField:{$exists:false}})` and update them with a valid value. Example: `db.collection.updateMany({shardKeyField:{$exists:false}},{$set:{shardKeyField:0}})`
  2. 80% success If the shard key is compound, ensure all fields in the shard key exist and are non-null. Use `db.collection.find({$or:[{field1:{$exists:false}},{field2:{$exists:false}}]})` to identify problematic documents. 
    If the shard key is compound, ensure all fields in the shard key exist and are non-null. Use `db.collection.find({$or:[{field1:{$exists:false}},{field2:{$exists:false}}]})` to identify problematic documents.
  3. 70% success As a last resort, export the collection, drop it, and re-import with proper shard key values. Example: `mongodump --collection mycollection; db.mycollection.drop(); sh.shardCollection('mydb.mycollection',{shardKey:1}); mongorestore --collection mycollection` 
    As a last resort, export the collection, drop it, and re-import with proper shard key values. Example: `mongodump --collection mycollection; db.mycollection.drop(); sh.shardCollection('mydb.mycollection',{shardKey:1}); mongorestore --collection mycollection`

中文步骤

  1. Find documents with missing or null shard key fields using a query like `db.collection.find({shardKeyField:{$exists:false}})` and update them with a valid value. Example: `db.collection.updateMany({shardKeyField:{$exists:false}},{$set:{shardKeyField:0}})`
  2. If the shard key is compound, ensure all fields in the shard key exist and are non-null. Use `db.collection.find({$or:[{field1:{$exists:false}},{field2:{$exists:false}}]})` to identify problematic documents.
  3. As a last resort, export the collection, drop it, and re-import with proper shard key values. Example: `mongodump --collection mycollection; db.mycollection.drop(); sh.shardCollection('mydb.mycollection',{shardKey:1}); mongorestore --collection mycollection`

Dead Ends

Common approaches that don't work:

  1. 20% fail

    This corrupts the sharding metadata and can cause data loss or cluster instability.

  2. 15% fail

    The balancer is not the root cause; the documents with missing shard keys remain, so any future split will fail.

  3. 25% fail

    If the shard key is compound, adding a single field may not resolve the issue and could violate shard key constraints.