This section describes failure handing at different stages of a cloning operation.
Prerequisites are checked (see Remote Cloning Prerequisites).
If a failure occurs during the prerequisite check, the
CLONE INSTANCEoperation reports an error.
Prior to MySQL 8.0.27, a backup lock on the donor and recipient blocks concurrent DDL operations. From MySQL 8.0.27, concurrent DDL on the donor is blocked only if the
clone_block_ddlvariable is enabled (it is disabled by default). See Section 126.96.36.199, “Cloning and Concurrent DDL”.
If the cloning operation is unable to obtain a DDL lock within the time limit specified by the
clone_ddl_timeoutvariable, an error is reported.
User-created data (schemas, tables, tablespaces) and binary logs on the recipient are removed before data is cloned to the recipient data directory.
When user created data is removed from the recipient during a remote cloning operation, existing data in the recipient data directory is not saved and may be lost if a failure occurs. If the data to be replaced on the recipient is of importance, a backup should be taken before initiating a remote cloning operation.
For informational purposes, warnings are printed to the server error log to specify when data removal starts and finishes:
[Warning] [MY-013453] [InnoDB] Clone removing all user data for provisioning: Started... [Warning] [MY-013453] [InnoDB] Clone removing all user data for provisioning: Finished
If a failure occurs while removing data, the recipient may be left with a partial set of schemas, tables, and tablespaces that existed before the cloning operation. Any time during the execution of a cloning operation or after a failure, the server is always in a consistent state.
Data is cloned from the donor. User-created data, dictionary metadata, and other system data are cloned.
If a failure occurs while cloning data, the cloning operation is rolled back and all cloned data removed. At this stage, the previously existing data on the recipient has also been removed, which leaves the recipient with no user data.
Should this scenario occur, you can either rectify the cause of the failure and re-execute the cloning operation, or forgo the cloning operation and restore the recipient data from a backup taken before the cloning operation.
The server is restarted automatically (applies to remote cloning operations that do not clone to a named directory). During startup, typical server startup tasks are performed.
If the automatic server restart fails, you can restart the server manually to complete the cloning operation.
Before MySQL 8.0.24, if a network error occurs during a cloning
operation, the operation resumes if the error is resolved within
five minutes. From MySQL 8.0.24, the operation resumes if the
error is resolved within the time specified by the
variable defined on the donor instance. The
default setting is 5 minutes but a range of 0 to 30 minutes is
supported. If the operation does not resume within the allotted
time, it aborts and returns an error, and the donor drops the
snapshot. A setting of zero causes the donor to drop the
snapshot immediately when a network error occurs. Configuring a
longer timeout allows more time for resolving network issues but
also increases the size of the delta on the donor instance,
which increases clone recovery time as well as replication lag
in cases where the clone is intended as a replica or replication
Prior to MySQL 8.0.24, donor threads use the MySQL Server
wait_timeout setting when
listening for Clone protocol commands. As a result, a low
wait_timeout setting could
cause a long running remote cloning operation to timeout. From
MySQL 8.0.24, the Clone idle timeout is set to the default
wait_timeout setting, which is
28800 seconds (8 hours).