KYLIN-4567 Improve TopN merge performance in MR engine

[guangxuCheng]

Proposed changes

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Types of changes

What types of changes does your code introduce to Kylin? Put an x in the boxes that apply

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation Update (if none of the other choices apply)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• [x] I have create an issue on Kylin's jira, and have described the bug/feature there in detail
• [x] Commit messages in my PR start with the related jira ID, like "KYLIN-0000 Make Kylin project open-source"
• [x] Compiling and unit tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] If this change need a document change, I will prepare another pr against the document branch
• [x] Any dependent changes have been merged

Further comments

If this is a relatively large or complex change, kick off the discussion at user@kylin or dev@kylin by explaining why you chose the solution you did and what alternatives you considered, etc...

[codecov-commenter]

Codecov Report

Merging #1259 into master will decrease coverage by 0.28%. The diff coverage is 14.31%.

@@             Coverage Diff              @@
##             master    #1259      +/-   ##
============================================
- Coverage     25.71%   25.43%   -0.29%     
- Complexity     6626     6732     +106     
============================================
  Files          1484     1505      +21     
  Lines         91185    93324    +2139     
  Branches      12726    13086     +360     
============================================
+ Hits          23452    23733     +281     
- Misses        65431    67252    +1821     
- Partials       2302     2339      +37     

Impacted Files	Coverage Δ	Complexity Δ
...main/java/org/apache/kylin/common/KylinConfig.java	38.29% <0.00%> (-2.08%)	29.00 <0.00> (+1.00)	:arrow_down:
.../java/org/apache/kylin/common/KylinConfigBase.java	12.70% <0.00%> (+0.99%)	51.00 <0.00> (+7.00)
...org/apache/kylin/common/restclient/RestClient.java	15.25% <0.00%> (-3.11%)	6.00 <1.00> (ø)
...n/java/org/apache/kylin/common/util/CheckUtil.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...c/main/java/org/apache/kylin/cube/CubeSegment.java	42.27% <0.00%> (-6.25%)	65.00 <0.00> (ø)
...rg/apache/kylin/cube/gridtable/CubeCodeSystem.java	22.07% <0.00%> (-3.30%)	8.00 <0.00> (ø)
.../org/apache/kylin/cube/model/AggregationGroup.java	77.15% <ø> (ø)	85.00 <0.00> (ø)
...ain/java/org/apache/kylin/cube/model/CubeDesc.java	58.15% <0.00%> (-4.14%)	182.00 <0.00> (ø)
...va/org/apache/kylin/cube/model/DictionaryDesc.java	48.57% <0.00%> (-16.82%)	8.00 <0.00> (ø)
...apache/kylin/cube/model/HBaseColumnFamilyDesc.java	23.80% <0.00%> (-14.66%)	4.00 <0.00> (ø)
... and 103 more

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[guangxuCheng]

@zzcclp update PR according to review comments. Thanks

[zzcclp]

@guangxuCheng there are some failed test cases, please fix them.

[guangxuCheng]

@guangxuCheng there are some failed test cases, please fix them.

@zzcclp Fixed. Please review, Thanks

[zzcclp]

@shaofengshi please review, thanks.

[coveralls]

Pull Request Test Coverage Report for Build 6158

• 18 of 23 (78.26%) changed or added relevant lines in 3 files are covered.
• 7 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.02%) to 28.04%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
core-common/src/main/java/org/apache/kylin/common/KylinConfigBase.java	0	1	0.0%
core-metadata/src/main/java/org/apache/kylin/measure/topn/TopNAggregator.java	0	4	0.0%
<!--	Total:	18	23

Files with Coverage Reduction	New Missed Lines	%
core-metadata/src/main/java/org/apache/kylin/measure/topn/TopNAggregator.java	1	0%
tool/src/main/java/org/apache/kylin/tool/query/ProbabilityGenerator.java	1	83.33%
core-cube/src/main/java/org/apache/kylin/cube/inmemcubing/MemDiskStore.java	5	77.81%
<!--	Total:	7

Totals
Change from base Build 6149:	0.02%
Covered Lines:	26240
Relevant Lines:	93579

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💛 - Coveralls

[zzcclp]

LGTM