Add some log to make it easier to observe data skew (#4404)

[ti-chi-bot]

This is an automated cherry-pick of #4404

What problem does this PR solve?

Issue Number: ref #4403, close #4427

Problem Summary:

What is changed and how it works?

Add some log to make it easier to observe data skew

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• SeaRise
• fuzhe1989

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[windtalker]

/merge

[ti-chi-bot]

@windtalker: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 6986042

[windtalker]

/run-all-tests

[sre-bot]

Coverage for changed files

Filename                                             Regions    Missed Regions     Cover   Functions  Missed Functions  Executed       Lines      Missed Lines     Cover    Branches   Missed Branches     Cover
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
DataStreams/ExchangeSenderBlockInputStream.cpp            27                27     0.00%           1                 1     0.00%          18                18     0.00%          10                10     0.00%
DataStreams/ExchangeSenderBlockInputStream.h              13                13     0.00%           4                 4     0.00%           9                 9     0.00%           4                 4     0.00%
DataStreams/TiRemoteBlockInputStream.h                   103               103     0.00%          15                15     0.00%         149               149     0.00%          56                56     0.00%
Storages/DeltaMerge/DMSegmentThreadInputStream.h          72                 7    90.28%           6                 0   100.00%          79                 2    97.47%          32                10    68.75%
Storages/DeltaMerge/DeltaMergeStore.cpp                 1325               467    64.75%          65                 5    92.31%        1895               427    77.47%         774               368    52.45%
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                                                   1540               617    59.94%          91                25    72.53%        2150               605    71.86%         876               448    48.86%

Coverage summary

Functions  MissedFunctions  Executed  Lines   MissedLines  Cover
16977      9541             43.80%    191319  96852        49.38%

full coverage report (for internal network access only)