fix empty segment cannot merge after gc and avoid write index data for empty dmfile

[lidezhu]

What problem does this PR solve?

Issue Number: close #4511

Problem Summary:

1. empty segments cannot be merged after gc;
2. the stable size is not 0 for empty dmfile because there is a '0' in every index file in such case;
3. when a segment can be triggerred to gc because of too many delete range, we still wait for the gc_safe_point change, which is not needed.

What is changed and how it works?

1. when segment should be gced because of too many delete range, do it regardless of the gc_safe_point;
2. only update index cache for read thread;
3. fix unstable rough set filter test because of more fast gc speed.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

1. load data into tiflash and check segment status;
   
2. set tiflash replica to 0 and check segment status after a while
   

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

Fix the problem that empty segments cannot be merged after gc

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• JaySon-Huang
• flowbehappy

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[lidezhu]

/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
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
DeltaMergeStore.cpp              1333               467    64.97%          64                 5    92.19%        1912               435    77.25%         778               368    52.70%
File/DMFilePackFilter.h           101                 6    94.06%          12                 1    91.67%         194                 6    96.91%          72                 7    90.28%
File/DMFileWriter.cpp             101                 8    92.08%          15                 0   100.00%         442                18    95.93%          70                 9    87.14%
File/DMFileWriter.h                24                 1    95.83%          14                 1    92.86%          37                 3    91.89%           6                 0   100.00%
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                            1559               482    69.08%         105                 7    93.33%        2585               462    82.13%         926               384    58.53%

Coverage summary

Functions  MissedFunctions  Executed  Lines   MissedLines  Cover
17044      9571             43.85%    191845  97042        49.42%

full coverage report (for internal network access only)

[sre-bot]

Coverage for changed files

Filename                                                Regions    Missed Regions     Cover   Functions  Missed Functions  Executed       Lines      Missed Lines     Cover    Branches   Missed Branches     Cover
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Debug/dbgFuncMisc.cpp                                        35                35     0.00%           2                 2     0.00%          56                56     0.00%          26                26     0.00%
Storages/DeltaMerge/ColumnFile/ColumnFileBig.cpp             68                 9    86.76%          12                 0   100.00%         168                20    88.10%          40                10    75.00%
Storages/DeltaMerge/DeltaMergeStore.cpp                    1342               478    64.38%          64                 5    92.19%        1917               442    76.94%         786               373    52.54%
Storages/DeltaMerge/File/DMFileBlockInputStream.cpp          12                 2    83.33%           2                 0   100.00%          44                 6    86.36%          12                 3    75.00%
Storages/DeltaMerge/File/DMFilePackFilter.h                 123                14    88.62%          12                 1    91.67%         202                 7    96.53%          88                15    82.95%
Storages/DeltaMerge/File/DMFileWriter.cpp                   101                 8    92.08%          15                 0   100.00%         442                18    95.93%          70                 9    87.14%
Storages/DeltaMerge/File/DMFileWriter.h                      24                 1    95.83%          14                 1    92.86%          37                 3    91.89%           6                 0   100.00%
Storages/DeltaMerge/StableValueSpace.cpp                    107                25    76.64%          15                 1    93.33%         275                66    76.00%          74                25    66.22%
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                                                      1812               572    68.43%         136                10    92.65%        3141               618    80.32%        1102               461    58.17%

Coverage summary

Functions  MissedFunctions  Executed  Lines   MissedLines  Cover
17069      9588             43.83%    192123  97199        49.41%

full coverage report (for internal network access only)

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #4513.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #4514.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #4515.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #4516.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #4517.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #4518.