[FLINK-13446][table-runtime-blink] Fix assign logic for row count sliding window

[hequn8128]

What is the purpose of the change

For blink planner, the Row count sliding window outputs incorrectly. The window assigner assigns less window than what expected. This means the window outputs fewer data.

This pull request fixes the window assigner and trigger logic, i.e., correct the window start and end calculation.

Brief change log

• Add trigger size property to CountWindow, because in some cases, the count window fires with a trigger size less than the window size.
• Correct the window start and end calculation in CountSlidingWindowAssigner.
• Correct existing test cases.

Verifying this change

This change is already covered by existing tests, such as GroupWindowITCase and WindowOperatorTest.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)

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Automated Checks

Last check on commit 70ee112 (Tue Aug 06 15:55:46 UTC 2019)

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Review Progress

• ❓ 1. The [description] looks good.
• ❓ 2. There is [consensus] that the contribution should go into to Flink.
• ❓ 3. Needs [attention] from.
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• ❓ 5. Overall code [quality] is good.

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CI report:

• 70ee112 : SUCCESS Build

[wuchong]

Thanks @hequn8128 , I left some comments.

[wuchong]

Do we miss "15L, 5L" here?

[hequn8128]

I think we have not missed outputs here.
For the slide window(size=5, slide=3), the first window is [-2,2], the second is [1, 5], so here, we only have one output for key2.

[wuchong]

What about to encode CountWindow as "countStart, countEnd" like TimeWindow. Then the logic of assigning windows will be similar to SlidingWindowAssigner which is much simpler IMO. What do you think?

[hequn8128]

Good idea.