Percona Live Online

This talk demonstrates the steps to repair a corrupted MongoDB Shard.

The main benefit of focusing on the repair of a corrupted shard as opposed to rebuilding the entire sharded cluster is obvious. Any required downtime is limited only to reading/writing of the corrupted shard and should take less time.

For the purpose of this talk, shard corruption is defined as when a shard has a collection with a different UUID as compared to the other shards, and/or different from the UUID in config.collections document for the namespace. Corrupted UUID could be the result of someone dropping the collection directly on the shard, and the restoring the collection to that shard.

A simple Google Search on “mongodb invalid uuid” would demonstrate that this problem has been encountered by multiple mongodb installations world-wide.