Shard a previously unsharded MongoDB collection and choose an appropriate shard key with sh.shardCollection()
domain: mongodb.com · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Analyze query patterns and pick a shard key field (or compound key) balancing high cardinality, even value frequency, and non-monotonic write distribution
Create a supporting index on the shard key field(s) if one doesn't already exist, since shardCollection requires it
Enable sharding on the database with sh.enableSharding(<db>) if it isn't already enabled
Run sh.shardCollection("<db>.<collection>", { <shardKeyField>: 1 }) — or { field: "hashed" } for a hashed shard key — to shard the collection
Monitor initial chunk distribution and the balancer via sh.status() to confirm chunks spread evenly across shards
Known gotchas
The shard key is effectively fixed for the collection's life in this workflow — a poor choice (low cardinality, monotonically increasing) causes jumbo chunks or hot shards that are hard to fix later
Monotonically increasing shard keys (like a timestamp or ObjectId) route all new inserts to one chunk/shard, creating a write bottleneck — use a hashed shard key to avoid this
shardCollection requires an index on the shard key prefix to already exist; the command errors out otherwise
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