Bug #100925 The Mgr parameter does not match the description in the official MySQL document
Submitted: 23 Sep 2020 9:02 Modified: 24 Sep 2020 17:49
Reporter: jiaona chen Email Updates:
Status: Closed Impact on me:
None 
Category:MySQL Server: Group Replication Severity:S2 (Serious)
Version:8.0.20, 8.0.21 OS:Ubuntu
Assigned to: CPU Architecture:Any

[23 Sep 2020 9:02] jiaona chen
Description:
The Mgr parameter does not match the description in the official MySQL document!

MySQL8.0.20 descriptions:
This system variable should have the same value on all group members. The value of this system variable can be changed while Group Replication is running. The change takes effect on each group member after you stop and restart Group Replication on the member. During this process, the value of the system variable is permitted to differ between group members, but message delivery will not have the same efficiency on all members.

configuration fileļ¼š
[mysqld]
basedir=/usr/local/mysql80
datadir=/data/mysql80/data
user=mysql
port=3380
socket=/tmp/mysql80.sock
log_error=/tmp/mysql80.log
log_bin=/data/mysql80/mysql-bin

gtid-mode=on            
enforce-gtid-consistency=on   
master-info-repository=TABLE    
relay-log-info-repository=TABLE 
binlog-checksum=none            
log-slave-updates=on            
log-bin=binlog                  
binlog-format=ROW               
 
transaction-write-set-extraction=XXHASH64                
loose-group_replication_group_name='ce9be252-2b71-11e6-b8f4-00212844f856'
loose-group_replication_start_on_boot=off                
loose-group_replication_local_address='db01:33061'        
loose-group_replication_group_seeds='db01:33061,db02:33062,db03:33063' 
loose-group_replication_bootstrap_group=off             
[mysql]
socket=/tmp/mysql80.sock

How to repeat:
mysql> set global group_replication_communication_max_message_size=524288000;
ERROR 3093 (HY000): The communication_max_message_size option cannot be set while Group Replication is running
[23 Sep 2020 13:05] MySQL Verification Team
Hello jiaona chen,

Thank you for the report and feedback.
Verified as described with 8.0.21 build.

regards,
Umesh
[23 Sep 2020 13:08] MySQL Verification Team
MySQL Server 8.0.21 test results

Attachment: 100925_8.0.21.results.txt (text/plain), 12.57 KiB.

[24 Sep 2020 17:49] Margaret Fisher
Posted by developer:
 
Thanks for pointing this out. I've changed to:

group_replication_communication_max_message_size

This system variable should have the same value on all group members. You cannot change the value of this system variable while Group Replication is running. You must stop Group Replication, change the value of the system variable, then restart Group Replication, on each of the group members. During this process, the value of the system variable is permitted to differ between group members, but some transactions on group members might be rolled back.