Zhen Wang

> I fired three threads to run these tasks in parallel. Are you using the same session for all threads?

 Do you mean `host1` is always shown here?

> Yes. Actually I found that Kyuubi use hive beeline to do this. Maybe this issue need to be solved in Hive source code. This is the connection url substring,...

The abstraction of SessionStore does not need to store Session objects, but only needs to store sessionHandle and Engine instance. We can add Cache layer to cache Session objects, MemorySessionStore...

I want to do it, assign myself.

I verified this patch is ok in our environment. Environment: + Kyuubi zookeeper client version: 3.6.3 + Zookeeper server version: 3.4.13 Check items: + Connect normally using Zookeeper Service Discovery...

run `bin/kyuubi-zk-cli` error: ``` Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/cli/ParseException at org.apache.zookeeper.ZooKeeperMain.(ZooKeeperMain.java:108) Caused by: java.lang.ClassNotFoundException: org.apache.commons.cli.ParseException at java.net.URLClassLoader.findClass(URLClassLoader.java:381) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ... 1 more ```

> I want to implement it please assign me. Thanks, assigned.

cc @cfmcgrady

unset conf doesn't seem to be a good way: ``` set kyuubi.operation.plan.only.mode=parser; // success select 1; // exception select 1; // success without plan mode ``` we can add `UNKNOWN`...