ClickHouse mutation operation triggers Zero Copy Replication deletion bug

Running mutation operations (like materializing an index) on ClickHouse clusters with Zero Copy Replication enabled can trigger a bug where replicas incorrectly identify all data parts as unreferenced and delete them from shared S3 storage. The deletion propagates across all replicas because they share the same storage backend.

Disable Zero Copy Replication immediately on all clusters. Before running mutations on production clusters, test on non-production environments first. Implement pre-mutation snapshots or enable S3 Versioning for critical data. Monitor S3 deletion activity during and after mutation operations.