Backups

ClickHouse® is currently at the design stage of creating some universal backup solution. Some custom backup strategies are:

1. Each shard is backed up separately.
2. FREEZE the table/partition. For more information, see Alter Freeze Partition.
   1. This creates hard links in shadow subdirectory.
3. rsync that directory to a backup location, then remove that subfolder from shadow.
   1. Cloud users are recommended to use Rclone.
4. Always add the full contents of the metadata subfolder that contains the current DB schema and ClickHouse configs to your backup.
5. For a second replica, it’s enough to copy metadata and configuration.
6. Data in ClickHouse is already compressed with lz4, backup can be compressed bit better, but avoid using cpu-heavy compression algorithms like gzip, use something like zstd instead.

The tool automating that process: Altinity Backup for ClickHouse.