mongodb sharding_error ai_generated true

MongoServerError: chunk too large to move: data size exceeds maximum chunk size

ID: mongodb/sharding-chunk-too-large

Also available as: JSON · Markdown
78%Fix Rate
83%Confidence
3Evidence
2023-01-01First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
7 active — — —

Root Cause

Chunk exceeds maximum size (default 128MB) and cannot be migrated. Caused by poor shard key choice leading to jumbo chunks.

generic

Workarounds

  1. 85% success Split the jumbo chunk manually 
    sh.splitAt('mydb.collection', { shardKeyField: splitPoint })  # find splitPoint with db.collection.find().sort({shardKey:1}).skip(N)

    Sources: https://www.mongodb.com/docs/manual/administration/

  2. 82% success Refine the shard key to increase cardinality (MongoDB 5.0+) 
    sh.refineCollectionShardKey('mydb.collection', { existingKey: 1, newField: 1 })  # adds suffix field
  3. 78% success Clear the jumbo flag after manual splitting 
    db.adminCommand({ clearJumboFlag: 'mydb.collection', bounds: [{ key: MinKey }, { key: MaxKey }] })

Dead Ends

Common approaches that don't work:

  1. Increase chunkSize to accommodate the large chunks 80% fail

    Larger chunks reduce balancer effectiveness. The root issue is shard key cardinality, not chunk size.

  2. Manually move the jumbo chunk with force flag 75% fail

    Force-moving jumbo chunks can cause out-of-memory on the target shard during migration.