Fix potential data inconsistency under heavy ddl operation

[lidezhu]

What problem does this PR solve?

Issue Number: ref #5032

Problem Summary: Currently we cache decoding schema for decoding raft data if a table schema doesn't change. And we judge whether a table schema has changed based on the table schema version.

But the schema version is not strictly consistent with the actual table schema which can be seen at https://github.com/pingcap/tiflash/blob/master/dbms/src/TiDB/Schema/SchemaBuilder.cpp#L362. That is when applying different schema changes in a diff, the table schema version will be set to the latest schema version after the first schema change is applied.

More concretely, when a lossy ddl change occurs, it will trigger drop column and add column schema changes and also rewrite some data at the same time. 
The schema changes will be applied one by one, and because tiflash updates the table schema version ahead of time when applying schema diff, after applying the drop column schema change, it will update the schema version to the latest schema version.

And if the decode thread tries to obtain the current schema for decoding data before the add column is applied, the current schema and the latest schema version will be cached. Then after the subsequent add column operation is applied, the table schema version will not be updated, so the cache of the decode thread will not be invalidated.

Therefore, the decode thread will decode the new data with an older schema, considering that the new added column is a dropped column and discarding it.

In addition, there is a lower chance of triggering this problem in the case of frequent add column and insert data.

cherry pick of #5044

What is changed and how it works?

Add an internal schema version for DecodingStorageSchemaSnapshot.

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

Fix potential data inconsistency under heavy ddl operation

[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
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Common/FailPoint.cpp                                         458                53    88.43%           6                 0   100.00%          56                 4    92.86%         152                53    65.13%
Debug/dbgFuncSchema.cpp                                       50                50     0.00%           5                 5     0.00%          77                77     0.00%          30                30     0.00%
Storages/IManageableStorage.h                                 20                18    10.00%          20                18    10.00%          38                36     5.26%           0                 0         -
Storages/StorageDeltaMerge.cpp                               679               328    51.69%          58                26    55.17%        1307               725    44.53%         378               243    35.71%
Storages/StorageDeltaMerge.h                                  11                 6    45.45%          11                 6    45.45%          17                 8    52.94%           0                 0         -
Storages/Transaction/DecodingStorageSchemaSnapshot.h          35                 1    97.14%           1                 0   100.00%          61                 1    98.36%          26                 2    92.31%
Storages/Transaction/PartitionStreams.cpp                    262               213    18.70%          21                13    38.10%         569               391    31.28%         138               117    15.22%
Storages/Transaction/SchemaBuilder.cpp                       846               805     4.85%          47                43     8.51%        1065               993     6.76%         492               472     4.07%
Storages/Transaction/TiDBSchemaSyncer.h                      140               132     5.71%          13                 9    30.77%         125               100    20.00%          52                51     1.92%
Storages/Transaction/tests/RowCodecTestUtils.h                80                 4    95.00%          14                 0   100.00%         168                 1    99.40%          30                 2    93.33%
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                                                       2581              1610    37.62%         196               120    38.78%        3483              2336    32.93%        1298               970    25.27%

Coverage summary

Functions  MissedFunctions  Executed  Lines   MissedLines  Cover
18239      9791             46.32%    204265  98086        51.98%

full coverage report (for internal network access only)

[JaySon-Huang]

LGTM

[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
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Common/FailPoint.cpp                                         458                53    88.43%           6                 0   100.00%          56                 4    92.86%         152                53    65.13%
Debug/dbgFuncSchema.cpp                                       50                50     0.00%           5                 5     0.00%          77                77     0.00%          30                30     0.00%
Storages/IManageableStorage.h                                 20                18    10.00%          20                18    10.00%          38                36     5.26%           0                 0         -
Storages/StorageDeltaMerge.cpp                               679               328    51.69%          58                26    55.17%        1307               725    44.53%         378               243    35.71%
Storages/StorageDeltaMerge.h                                  11                 6    45.45%          11                 6    45.45%          17                 8    52.94%           0                 0         -
Storages/Transaction/DecodingStorageSchemaSnapshot.h          35                 1    97.14%           1                 0   100.00%          61                 1    98.36%          26                 2    92.31%
Storages/Transaction/PartitionStreams.cpp                    262               213    18.70%          21                13    38.10%         569               391    31.28%         138               117    15.22%
Storages/Transaction/SchemaBuilder.cpp                       846               805     4.85%          47                43     8.51%        1065               993     6.76%         492               472     4.07%
Storages/Transaction/TiDBSchemaSyncer.h                      140               132     5.71%          13                 9    30.77%         125               100    20.00%          52                51     1.92%
Storages/Transaction/tests/RowCodecTestUtils.h                80                 4    95.00%          14                 0   100.00%         168                 1    99.40%          30                 2    93.33%
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                                                       2581              1610    37.62%         196               120    38.78%        3483              2336    32.93%        1298               970    25.27%

Coverage summary

Functions  MissedFunctions  Executed  Lines   MissedLines  Cover
18239      9791             46.32%    204265  98052        52.00%

full coverage report (for internal network access only)

[lidezhu]

/merge

[ti-chi-bot]

@lidezhu: 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: 57d9908

[sre-bot]

Coverage for changed files

Filename                                                 Regions    Missed Regions     Cover   Functions  Missed Functions  Executed       Lines      Missed Lines     Cover    Branches   Missed Branches     Cover
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Common/FailPoint.cpp                                         458                53    88.43%           6                 0   100.00%          56                 4    92.86%         152                53    65.13%
Debug/dbgFuncSchema.cpp                                       50                50     0.00%           5                 5     0.00%          77                77     0.00%          30                30     0.00%
Storages/IManageableStorage.h                                 20                18    10.00%          20                18    10.00%          38                36     5.26%           0                 0         -
Storages/StorageDeltaMerge.cpp                               679               328    51.69%          58                26    55.17%        1307               725    44.53%         378               243    35.71%
Storages/StorageDeltaMerge.h                                  11                 6    45.45%          11                 6    45.45%          17                 8    52.94%           0                 0         -
Storages/Transaction/DecodingStorageSchemaSnapshot.h          35                 1    97.14%           1                 0   100.00%          61                 1    98.36%          26                 2    92.31%
Storages/Transaction/PartitionStreams.cpp                    262               213    18.70%          21                13    38.10%         569               391    31.28%         138               117    15.22%
Storages/Transaction/SchemaBuilder.cpp                       846               805     4.85%          47                43     8.51%        1065               993     6.76%         492               472     4.07%
Storages/Transaction/TiDBSchemaSyncer.h                      140               132     5.71%          13                 9    30.77%         125               100    20.00%          52                51     1.92%
Storages/Transaction/tests/RowCodecTestUtils.h                80                 4    95.00%          14                 0   100.00%         168                 1    99.40%          30                 2    93.33%
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                                                       2581              1610    37.62%         196               120    38.78%        3483              2336    32.93%        1298               970    25.27%

Coverage summary

Functions  MissedFunctions  Executed  Lines   MissedLines  Cover
18239      9791             46.32%    204265  98070        51.99%

full coverage report (for internal network access only)