#### 17.1.3.6 Replication From a Source Without GTIDs to a Replica With GTIDs

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 From MySQL 8.0.23, you can set up replication channels to assign a GTID to replicated transactions that do not already have one. This feature enables replication from a source server that does not have GTIDs enabled and does not use GTID-based replication, to a replica that has GTIDs enabled. If it is possible to enable GTIDs on the replication source server, as described in [Section 17.1.4, “Changing GTID Mode on Online Servers”](replication-mode-change-online.html), use that approach instead. This feature is designed for replication source servers where you cannot enable GTIDs. Note that as is standard for MySQL replication, this feature does not support replication from MySQL source servers earlier than the previous release series, so MySQL 5.7 is the earliest supported source for a MySQL 8.0 replica.

 You can enable GTID assignment on a replication channel using the `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` option of the [`CHANGE REPLICATION SOURCE TO`](change-replication-source-to.html) statement. `LOCAL` assigns a GTID including the replica's own UUID (the [`server_uuid`](replication-options.html#sysvar_server_uuid) setting). `*`uuid`*` assigns a GTID including the specified UUID, such as the [`server_uuid`](replication-options.html#sysvar_server_uuid) setting for the replication source server. Using a nonlocal UUID lets you differentiate between transactions that originated on the replica and transactions that originated on the source, and for a multi-source replica, between transactions that originated on different sources. If any of the transactions sent by the source do have a GTID already, that GTID is retained.

Important

 A replica set up with `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` on any channel cannot be promoted to replace the replication source server in the event that a failover is required, and a backup taken from the replica cannot be used to restore the replication source server. The same restriction applies to replacing or restoring other replicas that use `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` on any channel.

 The replica must have [`gtid_mode=ON`](replication-options-gtids.html#sysvar_gtid_mode) set, and this cannot be changed afterwards, unless you remove the `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS=ON` setting. If the replica server is started without GTIDs enabled and with `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` set for any replication channels, the settings are not changed, but a warning message is written to the error log explaining how to change the situation.

 For a multi-source replica, you can have a mix of channels that use `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS`, and channels that do not. Channels specific to Group Replication cannot use `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS`, but an asynchronous replication channel for another source on a server instance that is a Group Replication group member can do so. For a channel on a Group Replication group member, do not specify the Group Replication group name as the UUID for creating the GTIDs.

 Using `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` on a replication channel is not the same as introducing GTID-based replication for the channel. The GTID set ([`gtid_executed`](replication-options-gtids.html#sysvar_gtid_executed)) from a replica set up with `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` should not be transferred to another server or compared with another server's [`gtid_executed`](replication-options-gtids.html#sysvar_gtid_executed) set. The GTIDs that are assigned to the anonymous transactions, and the UUID you choose for them, only have significance for that replica's own use. The exception to this is any downstream replicas of the replica where you enabled `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS`, and any servers that were created from a backup of that replica.

 If you set up any downstream replicas, these servers do not have `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` enabled. Only the replica that is receiving transactions directly from the non-GTID source server needs to have `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` set on the relevant replication channel. Among that replica and its downstream replicas, you can compare GTID sets, fail over from one replica to another, and use backups to create additional replicas, as you would in any GTID-based replication topology. `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` is used where transactions are received from a non-GTID server outside this group.

 A replication channel using `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` has the following behavior differences to GTID-based replication:

* GTIDs are assigned to the replicated transactions when they are applied (unless they already had a GTID). A GTID would normally be assigned on the replication source server when the transaction is committed, and sent to the replica along with the transaction. On a multi-threaded replica, this means the order of the GTIDs does not necessarily match the order of the transactions, even if [`slave-preserve-commit-order=1`](replication-options-replica.html#sysvar_slave_preserve_commit_order) is set.

* The `SOURCE_LOG_FILE` and `SOURCE_LOG_POS` options of the [`CHANGE REPLICATION SOURCE TO`](change-replication-source-to.html) statement are used to position the replication I/O (receiver) thread, rather than the `SOURCE_AUTO_POSITION` option.

* The `SET GLOBAL sql_replica_skip_counter` or `SET GLOBAL sql_slave_skip_counter` statement is used to skip transactions on a replication channel set up with `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS`, rather than the method of committing empty transactions. For instructions, see [Section 17.1.7.3, “Skipping Transactions”](replication-administration-skip.html).

* The `UNTIL SQL_BEFORE_GTIDS` and `UNTIL_SQL_AFTER_GTIDS` options of the [`START REPLICA`](start-replica.html) statement cannot be used for the channel.

* The function `WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS()`, which is deprecated from MySQL 8.0.18, cannot be used with the channel. Its replacement `WAIT_FOR_EXECUTED_GTID_SET()`, which works across the server, can be used to wait for any downstream replicas of the server that has `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` enabled. To wait for the channel with `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` enabled to catch up with the source, which does not use GTIDs, use the `SOURCE_POS_WAIT()` function (from MySQL 8.0.26) or the `MASTER_POS_WAIT()` function.

 The Performance Schema table [`replication_applier_configuration`](performance-schema-replication-applier-configuration-table.html) shows whether GTIDs are assigned to anonymous transactions on a replication channel, what the UUID is, and whether it is the UUID of the replica server (`LOCAL`) or a user-specified UUID (`MANUAL`). The information is also recorded in the applier metadata repository. A [`RESET REPLICA ALL`](reset-replica.html) statement resets the `ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS` setting, but a [`RESET REPLICA`](reset-replica.html) statement does not.

