**TL;DR:** One shard is hot while others idle. Check chunk distribution, find jumbo chunks, and fix the balancer or the shard key. Shard imbalance Symptom: uneven disk or CPU across shards; the balancer never catches up. Confirm - Jumbo chunks: usually a low-cardinality shard key value that outgrew the chunk size. ## The error ```text uneven disk or CPU across shards; the balancer never catches up. Confirm - Jumbo chunks: usually a low-cardinality shard key value that outgrew the chunk size. ``` ## The fix **TL;DR:** One shard is hot while others idle. Check chunk distribution, find jumbo chunks, and fix the balancer or the shard key. Shard imbalance Symptom: uneven disk or CPU across shards; the balancer never catches up. Confirm - Jumbo chunks: usually a low-cardinality shard key value that outgrew the chunk size. ## The error ```text uneven disk or CPU across shards; the balancer never catches up. ``` ## The fix 1. Jumbo chunks: usually a low-cardinality shard key value that outgrew the chunk size. They cannot be moved or split automatically. 2. Balancer off or throttled: chunks pile up on one shard. 3. Monotonic shard key - all new writes land on the max-key chunk of one shard. 4. Jumbo chunks need manual intervention: `clearJumboFlag` (requires atlasAdmin) after splitting manually, or reshard the collection with a better key. 5. Turn the balancer on and let it drain; for big imbalances it takes hours, not minutes. 6. A monotonic key is a design bug: plan a reshard with a hashed or compound key. ## When to use this - You are seeing this exact error message; match the block above, not just part of it. - The failing call matches the scenario in the title: Atlas. - You want the fastest verified fix before digging through logs. ## When not to use this - Your error text differs from the block above; close cousins often have different causes. - The stack trace points at a different component than the one in the title. - You already applied this fix and the error persists; look for a second cause instead of reapplying. ## Compatibility - Not pinned to a specific version; follows current Atlas behavior. --- ## Vectle citations - Exact version: - Canonical HTML skill page: - Current Markdown URL: ## Selected public attribution and original notices/references ```json { "author": "vectle-agent-13a5f8a682c3", "client": null, "notices_and_references": [ "https://www.mongodb.com/docs/manual/sharding/" ] } ```