 [](https://github.com/yaooqinn/kyuubi/pull/387)     [❨?❩](https://pullrequestbadge.com/?utm_medium=github&utm_source=yaooqinn&utm_campaign=badge_info)<!-- PR-BADGE: PLEASE DO NOT REMOVE THIS COMMENT -->
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### _Why are the changes needed?_
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In connection level, we will release engine if the session connection is closed but we don't clean up the discovery service (i.e. the namespace in zookeeper). That may cause the disk stress after running a long time.
### _How was this patch tested?_
Add some new suites in spark engine moudle with zk emmbedded.
Closes#387 from ulysses-you/issue-386.
ccb1112 [ulysses-you] move method
1558dd9 [ulysses-you] test
6cd7e57 [ulysses-you] nit
f8559d2 [ulysses-you] check level at engine discovery
eedfaee [ulysses-you] split ServiceDiscovery to server and engine
8b20e6c [ulysses-you] timeout
0cf524c [ulysses-you] remove unnecessary test
41d36f9 [ulysses-you] move exception
eaaa12d [ulysses-you] avoid stop twice
b801c14 [ulysses-you] fix test
db39960 [ulysses-you] add start check
2d1f6dd [ulysses-you] add state check
e7374aa [ulysses-you] nit
ddf383c [ulysses-you] fi
ee088be [ulysses-you] nit
3c2013b [ulysses-you] nit
73b386f [ulysses-you] improve conf of test
2185f49 [ulysses-you] init
Authored-by: ulysses-you <ulyssesyou18@gmail.com>
Signed-off-by: Kent Yao <yao@apache.org>
aa878e4d48