7.6.7.13 Clone System Variables

This section describes the system variables that control operation of the clone plugin. If values specified at startup are incorrect, the clone plugin may fail to initialize properly and the server does not load it. In this case, the server may also produce error messages for other clone settings because it does not recognize them.

Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. They can be changed dynamically at runtime using the SET statement, which enables you to modify operation of the server without having to stop and restart it.

Setting a global system variable runtime value normally requires the SYSTEM_VARIABLES_ADMIN privilege (or the deprecated SUPER privilege). For more information, see Section 7.1.9.1, “System Variable Privileges”.

Clone variables are configured on the recipient MySQL server instance where the cloning operation is executed.

• clone_autotune_concurrency

  Command-Line Format	--clone-autotune-concurrency
  Introduced	8.0.17
  System Variable	clone_autotune_concurrency
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  When clone_autotune_concurrency is enabled (the default), additional threads for remote cloning operations are spawned dynamically to optimize data transfer speed. The setting is applicable to recipient MySQL server instance only.

  During a cloning operation, the number of threads increases incrementally toward a target of double the current thread count. The effect on the data transfer speed is evaluated at each increment. The process either continues or stops according to the following rules:

  • If the data transfer speed degrades more than 5% with an incremental increase, the process stops.

  • If there is at least a 5% improvement after reaching 25% of the target, the process continues. Otherwise, the process stops.

  • If there is at least a 10% improvement after reaching 50% of the target, the process continues. Otherwise, the process stops.

  • If there is at least a 25% improvement after reaching the target, the process continues toward a new target of double the current thread count. Otherwise, the process stops.

  The autotuning process does not support decreasing the number of threads.

  The clone_max_concurrency variable defines the maximum number of threads that can be spawned.

  If clone_autotune_concurrency is disabled, clone_max_concurrency defines the number of threads spawned for a remote cloning operation.

• clone_buffer_size

  Command-Line Format	--clone-buffer-size
  Introduced	8.0.17
  System Variable	clone_buffer_size
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	4194304
  Minimum Value	1048576
  Maximum Value	268435456
  Unit	bytes

  Defines the size of the intermediate buffer used when transferring data during a local cloning operation. The default value is 4 mebibytes (MiB). A larger buffer size may permit I/O device drivers to fetch data in parallel, which can improve cloning performance.

• clone_block_ddl

  Command-Line Format	--clone-block-ddl
  Introduced	8.0.27
  System Variable	clone_block_ddl
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enables an exclusive backup lock on the donor MySQL Server instance during a cloning operation, which blocks concurrent DDL operations on the donor. See Section 7.6.7.4, “Cloning and Concurrent DDL”.

• clone_delay_after_data_drop

  Command-Line Format	--clone-delay-after-data-drop
  Introduced	8.0.29
  System Variable	clone_delay_after_data_drop
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	3600
  Unit	bytes

  Specifies a delay period immediately after removing existing data on the recipient MySQL Server instance at the start of a remote cloning operation. The delay is intended to provide enough time for the file system on the recipient host to free space before data is cloned from the donor MySQL Server instance. Certain file systems such as VxFS free space asynchronously in a background process. On these file systems, cloning data too soon after dropping existing data can result in clone operation failures due to insufficient space. The maximum delay period is 3600 seconds (1 hour). The default setting is 0 (no delay).

  This variable is applicable to remote cloning operation only and is configured on the recipient MySQL Server instance.

• clone_ddl_timeout

  Command-Line Format	--clone-ddl-timeout
  Introduced	8.0.17
  System Variable	clone_ddl_timeout
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	300
  Minimum Value	0
  Maximum Value	2592000
  Unit	seconds

  The time in seconds that a cloning operation waits for a backup lock. The backup lock blocks concurrent DDL when executing a cloning operation. This setting is applied on both the donor and recipient MySQL server instances.

  A setting of 0 means that the cloning operation does not wait for a backup lock. In this case, executing a concurrent DDL operation can cause the cloning operation to fail.

  Prior to MySQL 8.0.27, the backup lock blocks concurrent DDL operations on both the donor and recipient during a cloning operation, and a cloning operation cannot proceed until current DDL operations finish. As of MySQL 8.0.27, concurrent DDL is permitted on the donor during a cloning operation if clone_block_ddl variable is set to OFF (the default). In this case, the cloning operation does not have to wait for a backup lock on the donor. See Section 7.6.7.4, “Cloning and Concurrent DDL”.

• clone_donor_timeout_after_network_failure

  Command-Line Format	--clone-donor-timeout-after-network-failure
  Introduced	8.0.24
  System Variable	clone_donor_timeout_after_network_failure
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	5
  Minimum Value	0
  Maximum Value	30
  Unit	minutes

  Defines the amount of time in minutes the donor allows for the recipient to reconnect and restart a cloning operation after a network failure. For more information, see Section 7.6.7.9, “Remote Cloning Operation Failure Handling”.

  This variable is set on the donor MySQL server instance. Setting it on the recipient MySQL server instance has no effect.

• clone_enable_compression

  Command-Line Format	--clone-enable-compression
  Introduced	8.0.17
  System Variable	clone_enable_compression
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Enables compression of data at the network layer during a remote cloning operation. Compression saves network bandwidth at the cost of CPU. Enabling compression may improve the data transfer rate. This setting is only applied on the recipient MySQL server instance.

• clone_max_concurrency

  Command-Line Format	--clone-max-concurrency
  Introduced	8.0.17
  System Variable	clone_max_concurrency
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	16
  Minimum Value	1
  Maximum Value	128
  Unit	threads

  Defines the maximum number of concurrent threads for a remote cloning operation. The default value is 16. A greater number of threads can improve cloning performance but also reduces the number of permitted simultaneous client connections, which can affect the performance of existing client connections. This setting is only applied on the recipient MySQL server instance.

  If clone_autotune_concurrency is enabled (the default), clone_max_concurrency is the maximum number of threads that can be dynamically spawned for a remote cloning operation. If clone_autotune_concurrency is disabled, clone_max_concurrency defines the number of threads spawned for a remote cloning operation.

  A minimum data transfer rate of 1 mebibyte (MiB) per thread is recommended for remote cloning operations. The data transfer rate for a remote cloning operation is controlled by the clone_max_data_bandwidth variable.

• clone_max_data_bandwidth

  Command-Line Format	--clone-max-data-bandwidth
  Introduced	8.0.17
  System Variable	clone_max_data_bandwidth
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	1048576
  Unit	miB/second

  Defines the maximum data transfer rate in mebibytes (MiB) per second for a remote cloning operation. This variable helps manage the performance impact of a cloning operation. A limit should be set only when donor disk I/O bandwidth is saturated, affecting performance. A value of 0 means “unlimited”, which permits cloning operations to run at the highest possible data transfer rate. This setting is only applicable to the recipient MySQL server instance.

  The minimum data transfer rate is 1 MiB per second, per thread. For example, if there are 8 threads, the minimum transfer rate is 8 MiB per second. The clone_max_concurrency variable controls the maximum number threads spawned for a remote cloning operation.

  The requested data transfer rate specified by clone_max_data_bandwidth may differ from the actual data transfer rate reported by the DATA_SPEED column in the performance_schema.clone_progress table. If your cloning operation is not achieving the desired data transfer rate and you have available bandwidth, check I/O usage on the recipient and donor. If there is underutilized bandwidth, I/O is the next mostly likely bottleneck.

• clone_max_network_bandwidth

  Command-Line Format	--clone-max-network-bandwidth
  Introduced	8.0.17
  System Variable	clone_max_network_bandwidth
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	1048576
  Unit	miB/second

  Specifies the maximum approximate network transfer rate in mebibytes (MiB) per second for a remote cloning operation. This variable can be used to manage the performance impact of a cloning operation on network bandwidth. It should be set only when network bandwidth is saturated, affecting performance on the donor instance. A value of 0 means “unlimited”, which permits cloning at the highest possible data transfer rate over the network, providing the best performance. This setting is only applicable to the recipient MySQL server instance.

• clone_ssl_ca

  Command-Line Format	--clone-ssl-ca=file_name
  Introduced	8.0.14
  System Variable	clone_ssl_ca
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	empty string

  Specifies the path to the certificate authority (CA) file. Used to configure an encrypted connection for a remote cloning operation. This setting configured on the recipient and used when connecting to the donor.

• clone_ssl_cert

  Command-Line Format	--clone-ssl-cert=file_name
  Introduced	8.0.14
  System Variable	clone_ssl_cert
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	empty string

  Specifies the path to the public key certificate. Used to configure an encrypted connection for a remote cloning operation. This setting configured on the recipient and used when connecting to the donor.

• clone_ssl_key

  Command-Line Format	--clone-ssl-key=file_name
  Introduced	8.0.14
  System Variable	clone_ssl_key
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	empty string

  Specifies the path to the private key file. Used to configure an encrypted connection for a remote cloning operation. This setting configured on the recipient and used when connecting to the donor.

• clone_valid_donor_list

  Command-Line Format	--clone-valid-donor-list=value
  Introduced	8.0.17
  System Variable	clone_valid_donor_list
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	NULL

  Defines valid donor host addresses for remote cloning operations. This setting is applied on the recipient MySQL server instance. A comma-separated list of values is permitted in the following format: “HOST1:PORT1,HOST2:PORT2,HOST3:PORT3”. Spaces are not permitted.

  The clone_valid_donor_list variable adds a layer of security by providing control over the sources of cloned data. The privilege required to configure clone_valid_donor_list is different from the privilege required to execute remote cloning operations, which permits assigning those responsibilities to different roles. Configuring clone_valid_donor_list requires the SYSTEM_VARIABLES_ADMIN privilege, whereas executing a remote cloning operation requires the CLONE_ADMIN privilege.

  Internet Protocol version 6 (IPv6) address format is not supported. Internet Protocol version 6 (IPv6) address format is not supported. An alias to the IPv6 address can be used instead. An IPv4 address can be used as is.