[FLINK-15914][checkpointing][metrics] Miss the barrier alignment metric for the case of two inputs

[zhijiangW]

What is the purpose of the change

When the StreamTwoInputSelectableProcessor was introduced before, it was missing to add the barrier alignment metric in the constructor. But it does not cause problems then, because only StreamTwoInputProcessor works at that time. After StreamTwoInputProcessor is replaced by StreamTwoInputSelectableProcessor as now, this bug is exposed and we will not see the barrier alignment metric for the case of two inputs.

The solution is to add this metric while constructing the CheckpointBarrierHandler.

Brief change log

• Add the metric of barrier alignment while constructing the CheckpointBarrierHandler

Verifying this change

Via the job testing.

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

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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[pnowojski]

I would be fine with merging it as it is to release 1.10.

For master I would prefer the comments to be addressed and maybe add a test that metric is present? But it would be nice for at leat the production code be the same for 1.10 and master.

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CI report:

• 012203b Travis: FAILURE Azure: SUCCESS
• ac23472 Travis: FAILURE Azure: SUCCESS

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[pnowojski]

@zhijiangW if you think it's better to have this minimal change for release-1.10 and do the more proper fixes for master +1 from my side.

[zhijiangW]

Thanks for the review @pnowojski . I already submitted the updates.

[pnowojski]

LGTM, let's think about deduplication and test in the master version.

Let's also wait for green travis before merging.

[tillrohrmann]

The failing python build should be unrelated. See FLINK-15921. +1 for merging.