This guide walks through diagnosing a MongoDB outage, explains sharding concepts, shows when to shard, and provides step‑by‑step instructions for configuring config servers, mongos routers, converting replica sets, sharding collections, tracking chunks, and managing the balancer.
After upgrading a three‑shard MongoDB cluster from version 3.2 to 4.0, CPU usage jumped from 10 % to 40 % due to more frequent moveChunk operations and the resulting delete workload, as the balancer’s imbalance thresholds changed between versions.
The article examines why upgrading a three‑shard MongoDB cluster from version 3.2 to 4.0 causes CPU usage to jump from 10 % to 40 %, attributing the increase to more frequent moveChunk operations and the associated deletion workload, and explains the underlying balancer threshold differences between the versions.
A MongoDB client reported severe chunk imbalance and nightly balancer migration failures in a sharded cluster, which were traced to a known bug causing conflicting operations, and the issue was resolved by disabling the balancer for the affected collection and upgrading the cluster to version 3.4.11 or later.
This article explains MongoDB sharded clusters, covering data distribution, primary shard concepts, metadata collections, commands for moving primary shards, managing balancer settings, handling jumbo chunks, and procedures for adding or removing shards, with practical code examples for each operation.
This article explains the three scenarios that trigger MongoDB chunk migration, describes the Balancer's lock‑based operation, and walks through the six detailed steps—including tag‑based splits, draining shard handling, and load‑balancing thresholds—that ensure data is evenly distributed across shards.
