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### _Why are the changes needed?_
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This PR adds multiple engine support for non-connection share levels. A new configuration called `kyuubi.engine.share.level.sub.domain` is added for this functionality. For simplification, the configuration only accepts [1, 10]-length case insensitive string, only '_' and alphabets are valid.
Unlike connection mode, user mode supports the "long-running" feature across different JDBC connections. But the current implementation only is able to create one engine for a user. End-users don't want to put all eggs into one basket. It's not only less robust and flexible for a static engine to handle different workloads, and also hard to leverage failover when there is a zombied engine being cached.
With multiple engines support, end-users are able to
1. create as many engines as they want to meet the concurrency.
2. leverage different queue/namespace resource with long-running mode
3. can give different resources or priorities to their own engines for different workloads
4. can perform fast failover by creating a new sub domain
5. etc.
### _How was this patch tested?_
- [x] Add some test cases that check the changes thoroughly including negative and positive cases if possible
- [ ] Add screenshots for manual tests if appropriate
- [x] [Run test](https://kyuubi.readthedocs.io/en/latest/tools/testing.html#running-tests) locally before make a pull request
Closes#627 from yaooqinn/multipleengines.
Closes#627
9f04bc3e [Kent Yao] fix tests
d7af751e [Kent Yao] address comments
be9c46d8 [Kent Yao] address comments
ccce87d7 [Kent Yao] address comments
d49116c7 [Kent Yao] Support multiple engines for non-connection share levels
f1d8bc17 [Kent Yao] Support multiple engines for non-connection share levels
Authored-by: Kent Yao <yao@apache.org>
Signed-off-by: Cheng Pan <379377944@qq.com>
b4a505971c