每当一个成员加入或重新加入复制组时，它必须追赶在它加入之前或离开期间由组成员应用的事务。这个过程称为分布式恢复。Whenever a member joins or rejoins a replication group, it must catch up with the transactions that were applied by the group members before it joined, or while it was away. This process is called distributed recovery.

加入的成员首先检查其 group_replication_applier 通道的中继日志，查看它是否已经从组中接收到但尚未应用的任何事务。如果加入的成员此前曾在该组中，它可能会发现离开之前未应用的事务，在这种情况下，它将首先应用这些事务。对于新加入组的成员，则没有任何事务需要应用。The joining member begins by checking the relay log for its group_replication_applier channel for any transactions that it already received from the group but did not yet apply. If the joining member was in the group previously, it might find unapplied transactions from before it left, in which case it applies these as a first step. A member that is new to the group does not have anything to apply.

之后，加入的成员会连接到一个在线的现有成员以执行状态转移。加入的成员会转移在其加入之前或离开期间在群组中发生的所有事务，这些事务由现有成员提供（称为捐赠者）。接下来，加入的成员会应用在状态转移进行过程中群组中发生的事务。当此过程完成后，加入的成员已赶上群组中其余服务器的状态，并开始正常参与群组。After this, the joining member connects to an online existing member to carry out state transfer. The joining member transfers all the transactions that took place in the group before it joined or while it was away, which are provided by the existing member (called the donor). Next, the joining member applies the transactions that took place in the group while this state transfer was in progress. When this process is complete, the joining member has caught up with the remaining servers in the group, and it begins to participate normally in the group.

群组复制在分布式恢复期间的状态转移中使用这些方法的组合：Group Replication uses a combination of these methods for state transfer during distributed recovery:

在你对加入成员发出 START GROUP_REPLICATION 后，组复制会自动选择这些方法的最佳组合来进行状态传输。为此，组复制会检查哪些现有成员适合作为捐赠者，加入成员需要从捐赠者那里获取多少事务，以及是否有任何所需事务在任何组成员的二进制日志文件中已不再存在。如果加入成员与合适捐赠者之间的事务差距较大，或者某些所需事务在任何捐赠者的二进制日志文件中不存在，组复制将开始使用远程克隆操作的分布式恢复。如果事务差距不大，或者克隆插件未安装，组复制将直接从捐赠者的二进制日志进行状态传输。Group Replication automatically selects the best combination of these methods for state transfer after you issue START GROUP_REPLICATION on the joining member. To do this, Group Replication checks which existing members are suitable as donors, how many transactions the joining member needs from a donor, and whether any required transactions are no longer present in the binary log files on any group member. If the transaction gap between the joining member and a suitable donor is large, or if some required transactions are not in any donor's binary log files, Group Replication begins distributed recovery with a remote cloning operation. If there is not a large transaction gap, or if the clone plugin is not installed, Group Replication proceeds directly to state transfer from a donor's binary log.

当加入的成员与小组的所有事务同步时，它被宣布为在线状态，并可以作为普通成员参与小组，分布式恢复完成。When the joining member is up to date with all the group's transactions, it is declared online and can participate in the group as a normal member, and distributed recovery is complete.