We encountered issues with "Too many connections mysql" when trying to login to mysql. We also see that mysql is hanging and not providing a response.
We are noticing this after applying the November / December / January monthly platform patch where mysql is at 8.0.27 and greater.
# rpm -qa | grep mysql
Release : 10.0 10.1
Component : API GATEWAY
A major change in 8.0.27 was this changing of replication to default to the multithreader which was new.
According to the MySQL docs setting replica_parallel_workers=0 disables it.
Our Current Monthly Platform Patch of February 2022 addresses this.
If you are unable to apply the Monthly Patch you can follow the below manual steps instead.
Replication: Multithreading is now enabled by default for replica servers
Steps to remediate:
1) Stop SSG service
# service ssg stop
2) Stop replication
2A) Stop slave replication on both nodes: mysqladmin stop-slave
2B) Reset the master configuration on both nodes: mysql -e "reset master"
2C) Reset the slave configuration on both nodes: mysql -e "reset slave; reset slave all"
3) Update /etc/mysql.cnf to include replica_parallel_workers=0 in the [mysqld] section on both nodes.
# vi /etc/my.cnf on both nodes
**** my.cnf to look as below.
# Added on this date mm/dd/yyyy to use legacy replication
4) Restart mysql on both nodes.
# service mysql restart
5) Re-establish replication
Starting with the monthly Platform patch Layer7_API_PlatformUpdate_64bit_v10.X-CentOS-2022-03-29.L7P the fix in this KB addressed changes to /etc/my.cnf (Gateway Appliance only)
#Added to disable multithreaded replication from mysql 8.0.27 version