misc: Add comments

[breezewish]

What problem does this PR solve?

Issue Number: ref #4862

What is changed and how it works?

Added some comments when I go through the DeltaTree write path.

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:

• JaySon-Huang
• lidezhu

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[lidezhu]

LGTM

[JaySon-Huang]

LGTM

[JaySon-Huang]

/merge

[ti-chi-bot]

@JaySon-Huang: 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: e40485d

[sre-bot]

Coverage for changed files

Filename                                   Regions    Missed Regions     Cover   Functions  Missed Functions  Executed       Lines      Missed Lines     Cover    Branches   Missed Branches     Cover
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
DeltaMerge/ColumnFile/ColumnFile.h              19                 5    73.68%          19                 5    73.68%          23                 9    60.87%           0                 0         -
DeltaMerge/ColumnFile/ColumnFileTiny.h          24                 7    70.83%          15                 1    93.33%          36                 8    77.78%           6                 4    33.33%
DeltaMerge/Delta/DeltaValueSpace.h             107                22    79.44%          48                 4    91.67%         121                23    80.99%          36                13    63.89%
DeltaMerge/Delta/MemTableSet.cpp               119                24    79.83%           9                 0   100.00%         196                14    92.86%          96                25    73.96%
DeltaMerge/Delta/MemTableSet.h                   7                 0   100.00%           6                 0   100.00%          20                 0   100.00%           2                 0   100.00%
DeltaMerge/DeltaMergeHelpers.h                  91                 7    92.31%          21                 0   100.00%         167                 8    95.21%          56                10    82.14%
DeltaMerge/DeltaMergeStore.cpp                1392               464    66.67%          66                 5    92.42%        1981               436    77.99%         808               364    54.95%
DeltaMerge/DeltaMergeStore.h                    41                13    68.29%          19                 2    89.47%          91                30    67.03%          42                11    73.81%
DeltaMerge/RowKeyRange.h                       261                53    79.69%          63                13    79.37%         501                99    80.24%         166                48    71.08%
DeltaMerge/Segment.h                            34                 5    85.29%          22                 3    86.36%          31                 4    87.10%           6                 3    50.00%
IManageableStorage.h                            22                20     9.09%          22                20     9.09%          40                38     5.00%           0                 0         -
StorageDeltaMerge.cpp                          678               359    47.05%          57                27    52.63%        1303               758    41.83%         378               260    31.22%
StorageDeltaMerge.h                             11                 7    36.36%          11                 7    36.36%          17                 9    47.06%           0                 0         -
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                                         2806               986    64.86%         378                87    76.98%        4527              1436    68.28%        1596               738    53.76%

Coverage summary

Functions  MissedFunctions  Executed  Lines   MissedLines  Cover
18121      9785             46.00%    202195  97855        51.60%

full coverage report (for internal network access only)