Why should you care?

If one shard fills up while others are empty, inserts slow and disks risk filling. Balancing keeps capacity usable.

See it live — copy this example

Open mongosh or MongoDB Compass, select database nosqlverse, then run the example. Change one field and run again.

sh.getBalancerState()
sh.isBalancerRunning()
sh.startBalancer()
db.getSiblingDB("config").changelog.find({ what: /moveChunk/ }).sort({ time: -1 }).limit(3)
db.readings.getShardDistribution()

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• Balancer state shows whether automatic balancing is on.
• changelog records moveChunk events.
• getShardDistribution shows counts/sizes per shard after migrations.
• You can pause the balancer during peak sales if needed.

Practice next

1. Check balancer state on a sharded cluster.
2. Inspect distribution for a busy collection.
3. Read recent moveChunk changelog entries.
4. sh.disableAutoSplitter careful study in labs only.
5. Identify jumbo chunks in sh.status().

Remember

Chunks are shard key ranges. Balancer migrates chunks for evenness. Watch distribution and changelog.

Rebalance after adding a shard

Ops adds a fourth shard; balancer migrates chunks onto it overnight.

Outcome: Write load spreads across the new capacity by morning.