trouble of confluence 6.5 to connect mysql 8 on ubuntu 20.04

[zhihui zheng]

Hi. I have an a little bit old version of confluence 6.5 to run on my ubuntu 18.04 for a while. The database was mysql 5.X. 

Recently, I upgrade my ubuntu to 20.04 and also upgrade the mysql version to 8. Now it seems that I can not use my confluence now since it reporting:
MYSQL isolution level could not be read.

I did spend lots of time to find out that I also need to download new mysql-connector-8.xx.jar and put it to the right folder. But the problem is that even I managed to get the new mysql connector jar file and put into the right folder. I still could not have confluence 6.5 to connect to mysql (I did stop/start confluence when doing so).

Is there anyone can help me on this please? There are lots of my personal data on confluence. Thank you in advance. 

[zhihui zheng]

btw, isolution level is correctly configured in mysql 8:

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> SELECT @@GLOBAL.transaction_isolation, @@transaction_isolation;
+--------------------------------+-------------------------+
| @@GLOBAL.transaction_isolation | @@transaction_isolation |
+--------------------------------+-------------------------+
| READ-COMMITTED | READ-COMMITTED |
+--------------------------------+-------------------------+
1 row in set (0.00 sec)

[Nic Brough _Adaptavist_]

What does the log say the database connection errors are when Confluence starts up?

[Gonchik Tsymzhitov]

@zhihui zheng  Hm, if I were I will start upgrade of Confluence at least to 7.2 version. 

https://jira.atlassian.com/browse/CONFSERVER-52665

Because too risky works with unsupported 8.0 and old Confluence.