MySQL 8.0 Release Notes
MySQL 8.0 Source Code Documentation
The following function enables you to set a member of a single-primary replication group to take over as the primary. The current primary becomes a read-only secondary, and the specified group member becomes the read-write primary. The function can be used on any member of a replication group running in single-primary mode. This function replaces the usual primary election process. Section 18.5.1.1, “Changing a Group's Primary Member” explains the MySQL Server version requirements for the new primary member.
If a standard source to replica replication channel is running
on the existing primary member in addition to the Group
Replication channels, you must stop that replication channel
before you can change the primary member. You can identify the
current primary using the MEMBER_ROLE column
in the Performance Schema table
replication_group_members, or the
group_replication_primary_member
status variable.
Any uncommitted transactions that the group is waiting on must be committed, rolled back, or terminated before the operation can complete. Before MySQL 8.0.29, the function waits for all active transactions on the existing primary to end, including incoming transactions that are started after the function is used. From MySQL 8.0.29, you can specify a timeout for transactions that are running when you use the function. For the timeout to work, all members of the group must be at MySQL 8.0.29 or higher.
When the timeout expires, for any transactions that did not yet
reach their commit phase, the client session is disconnected so
that the transaction does not proceed. Transactions that reached
their commit phase are allowed to complete. When you set a
timeout, it also prevents new transactions starting on the
primary from that point on. Explicitly defined transactions
(with a START TRANSACTION or
BEGIN statement) are subject to the timeout,
disconnection, and incoming transaction blocking even if they do
not modify any data. To allow inspection of the primary while
the function is operating, single statements that do not modify
data, as listed in
Permitted Queries Under Consistency Rules, are
permitted to proceed.
group_replication_set_as_primary()Appoints a specific member of the group as the new primary, overriding any election process.
Syntax:
STRING group_replication_set_as_primary(member_uuid[, timeout])Arguments:
member_uuid: A string containing the UUID of the member of the group that you want to become the new primary.timeout: An integer specifying a timeout in seconds for transactions that are running on the existing primary when you use the function. You can set a timeout from 0 seconds (immediately) up to 3600 seconds (60 minutes). When you set a timeout, new transactions cannot start on the primary from that point on. There is no default setting for the timeout, so if you do not set it, there is no upper limit to the wait time, and new transactions can start during that time. This option is available from MySQL 8.0.29.
Return value:
A string containing the result of the operation, for example whether it was successful or not.
Example:
SELECT group_replication_set_as_primary(‘00371d66-3c45-11ea-804b-080027337932’, 300)For more information, see Section 18.5.1.1, “Changing a Group's Primary Member”.