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; see Section 20.5.1.1, “Changing the Primary”, for more information.

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 replication_group_members table.

Any uncommitted transactions that the group is waiting on must be committed, rolled back, or terminated before the operation can complete. 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 MySQL version 8.0.29 or newer.

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.