MySQL CLONE uses MySQL's native CLONE plugin to transfer data directly from a running MySQL server (the "donor") to a tablet being provisioned (the "recipient"). Unlike traditional backup and restore, CLONE copies data over the network at the physical level without staging in object storage. This makes provisioning faster, eliminates the storage intermediate, and lets the recipient start replicating from a position close to the donor's current state.

Requirements #

MySQL Version #

MySQL CLONE requires MySQL 8.0.17 or later on both donor and recipient servers. Cloning across point releases (e.g., 8.0.37 to 8.0.41) is not permitted before MySQL 8.0.37.

Storage Engine #

Only InnoDB tables can be cloned. If your databases contain MyISAM or other non-InnoDB tables, you cannot use MySQL CLONE.

Clone Plugin #

Both donor and recipient MySQL servers must have the mysql_clone.so plugin installed and active. Vitess can configure this automatically when you enable clone support (see Configuration below).

Permissions #

The clone user connecting to the donor must have BACKUP_ADMIN privilege, and the clone user on the recipient must have CLONE_ADMIN privilege. Vitess creates a vt_clone user with these privileges when you enable clone support.

Configuration #

Enabling Clone Support #

To enable MySQL CLONE, configure both the MySQL servers and the Vitess components.

MySQL Configuration:

When initializing MySQL with mysqlctl or mysqlctld, enable clone support:

mysqlctl --mysql-clone-enabled init

This flag loads the MySQL CLONE plugin (mysql_clone.so) and creates the vt_clone user with the required privileges (BACKUP_ADMIN, CLONE_ADMIN).

Clone Credentials:

Configure the clone user credentials for vtbackup and vttablet:

Example:

vttablet ... --db-clone-user=vt_clone \
             --db-clone-password=secret \
             --db-clone-use-ssl=false

Using CLONE with VTTablet #

You can use MySQL CLONE to provision a new vttablet instead of restoring from a backup.

Startup Flags:

Clone from Primary #

To provision a new tablet by cloning from the shard's primary:

vttablet --init-keyspace=commerce \
         --init-shard=0 \
         --init-tablet-type=replica \
         --restore-with-clone \
         --clone-from-primary \
         --db-clone-user=vt_clone \
         --db-clone-use-ssl=false

Clone from Specific Tablet #

To clone from a specific tablet (useful to avoid loading the primary):

vttablet --init-keyspace=commerce \
         --init-shard=0 \
         --init-tablet-type=replica \
         --restore-with-clone \
         --clone-from-tablet=zone1-0000000101 \
         --db-clone-user=vt_clone \
         --db-clone-use-ssl=false

Using CLONE with VTBackup #

VTBackup can use MySQL CLONE for its restore phase instead of restoring from the most recent backup. This can significantly speed up the backup process when the primary has data newer than the latest backup.

To run vtbackup with clone-based restore:

vtbackup --init-keyspace=commerce \
         --init-shard=0 \
         --mysql-clone-enabled \
         --restore-with-clone \
         --clone-from-primary \
         --db-clone-user=vt_clone \
         --db-clone-use-ssl=false

The --restore-with-clone flag tells vtbackup to clone from a donor tablet instead of restoring from backup storage. After the clone completes, vtbackup proceeds with its normal workflow: catching up on replication and taking a new backup.

Use Cases #

Initializing New Tablets #

When adding new replica tablets to a shard, MySQL CLONE can provision them faster than restoring from object storage backups. This is especially beneficial for large databases where backup restore times are significant.

Repairing Broken Replicas #

If replica tablets experience replication errors (such as HA_ERR_FOUND_DUPP_KEY or HA_ERR_KEY_NOT_FOUND) that prevent them from making progress, you can use MySQL CLONE to quickly reprovision them from the primary. This avoids the need to take a new backup or perform manual mysqldump operations.

Speeding Up VTBackup #

For shards with high write activity, the catch-up phase of vtbackup can be lengthy if the latest backup is old. Using CLONE, vtbackup starts with a dataset close to the primary's current state, minimizing the catch-up time.

Limitations #

• Both donor and recipient must run MySQL 8.0.17+.
• Only InnoDB tables can be cloned.
• A donor can only support one clone operation at a time.
• The recipient tablet must not be a primary tablet.
• Clone transfers data over the network, so ensure adequate bandwidth between donor and recipient.