Restore backup on a replica - still need to set gtid_purged?

MySQL & MariaDB Percona XtraBackup
1

In How to create a new (or repair a broken) GTID-based replica in step 4:

Set the gtid_purged variable to the GTID from xtrabackup_binlog_info. Then, update the information about the source node and, finally, start the replica.

After restoring from a backup in a replica, I found that the Executed_Gtid_Set is set and the value matches the one in xtrabackup_binlog_info in the backup folder.

Then, I continue with the following, without setting gtid_purged first.

> CHANGE REPLICATION SOURCE TO
             SOURCE_HOST="$masterip",
             SOURCE_USER="repl",
             SOURCE_PASSWORD="$slavepass",
             SOURCE_AUTO_POSITION = 1;
> START REPLICA;

and the replication was able to proceed without any error.

Do I still need to perform this?
SET GLOBAL gtid_purged='<gtid_string_found_in_xtrabackup_binlog_info>'; before CHANGE REPLICATION SOURCE and START REPLICA?

2

Yes, it is recommended to use SET gtid_purged because the backup directory doesn’t contain all the gtids/binlog files before the position/gtids recorded by xtrabackup.

xtrabackup doesn’t copy all the binlog files. So we should tell the server, that the start point of binlog/gtids is the position recorded in xtrabackup binlog_info files.