confluence.tenant.VacantException after upgrade from 6.0.2 to 6.2.2

[xkey]

The old discussions suggested that it could be 

1) Database issue. However, I was able to login to database using the same credential.

2) hostname. it has been running before, so I modified /etc/hosts, no use.

3) application-data/confluence/confluence.cfg.xml looks good for mysql definition

Any other possible reasons?

Host OS is 16.04

com.atlassian.confluence.tenant.VacantException: Confluence is vacant, a call to tenanted [public abstract org.hibernate.Session org.hibernate.SessionFactory.getCurrentSession() throws org.hibernate.HibernateException] is not allowed.
	com.atlassian.confluence.tenant.TenantGate$1.lambda$create$0(TenantGate.java:43)
	org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
	org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:208)
	com.sun.proxy.$Proxy54.getCurrentSession(Unknown Source)
	sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
 

[xkey]

Forgot to mention that I also upgraded from 14.04 to 16.04, which moved mysql to 5.7. After reading ther posts on this forum, there seemed to be a problem of mysql url where system unknown variables passed to jdcb and causing the problem.

This was apparent from application-data/confluence/logs/atlassian-confluence.log

i had to remove all Session Variables from url in confluence.cfg.xml

<property name="hibernate.connection.url">jdbc:mysql://localhost/confluence</property>

then it started to come up

Wondering if this would cause other problems especially for utf storage_engine and etc

[xkey]

<property name="hibernate.connection.url">jdbc:mysql://localhost/confluence?useUnicode=true&amp;characterEncoding=utf8</property>

no need to remove others

However, it still keeps complaining

2017-07-03 10:20:15,407 ERROR [localhost-startStop-1] [confluence.setup.dbcheck.MySQLChecker] checkStorageEngineType Your database Storage Engine could not be determined: Incorrect result size: expected 1, actual 0
org.springframework.dao.EmptyResultDataAccessException: Incorrect result size: expected 1, actual 0