* Refactor the code
* Add a new column xid for zookeeper_connection
* Support hostnames in the configuration
* Fix a typo
* Fix a typo
* Fix a typo
* Fix a bug about connect_time
* Update test case
* Update test case
* Fix a special build check error
* Resolve conflicts caused by rebase.
* Update failed test case
* Refactor the code according to comment
* Fix two compilation errors