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ddl: fix concurrent column type changes(with changing data) that cause schema and data inconsistencies #31051

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merged 5 commits into from
Dec 28, 2021
Merged

ddl: fix concurrent column type changes(with changing data) that cause schema and data inconsistencies #31051

merged 5 commits into from
Dec 28, 2021

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zimulala
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@zimulala zimulala commented Dec 27, 2021 •
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What problem does this PR solve?

Issue Number: close #31048

Problem Summary:

For column type changes, the column ID is changed if it is lossy.

If both sessions perform lossy column type changes((like modify column c int -> char)) simultaneously

  1. Connection1: execute DDL1, it will change column ID (ID :1-> ID :2)

  2. Connection2: execute DDL2. After DDL1 enters the DDL job queue and is not executed, then DDL2 enters the job queue.

  3. After DDL1 is executed successfully, DDL2 considers that the column is not lossy(char -> char), so it does not change the column ID, which is the old id:1. So id:1 overwrites id:2.

After DDL2 is completed, the column ID is still the original id:1 instead of the correct id:2.

Because the column ID was changed incorrectly, the schema could not match the data, resulting in decode failure when reading data.

What is changed and how it works?

In step 3, we check that the ID of the modified column is the same as the ID of the original column.

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 concurrent column type changes(with changing data) that cause schema and data inconsistencies.

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ti-chi-bot commented Dec 27, 2021 •
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[REVIEW NOTIFICATION]

This pull request has been approved by:

  • AilinKid
  • tangenta

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@ti-chi-bot ti-chi-bot added release-note Denotes a PR that will be considered when it comes time to generate release notes. size/M Denotes a PR that changes 30-99 lines, ignoring generated files. labels Dec 27, 2021
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sre-bot commented Dec 27, 2021 •
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Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/12962ce7f6a4125778c3bde248f967318a5e2726

AilinKid
AilinKid approved these changes Dec 27, 2021
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LGTM

@ti-chi-bot ti-chi-bot added the status/LGT1 Indicates that a PR has LGTM 1. label Dec 27, 2021
wjhuang2016
wjhuang2016 reviewed Dec 27, 2021
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ddl/db_change_test.go
@@ -1062,6 +1062,54 @@ func (s *testStateChangeSuite) TestParallelAlterModifyColumn(c *C) {
s.testControlParallelExecSQL(c, sql, sql, f)
}

func (s *testStateChangeSuite) TestParallelAlterModifyColumnWithData(c *C) {
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Can we add more tests about concurrent alter table? For example, random test.

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Could you give an example of this random test? I don't think it's appropriate to add it here.

@ti-chi-bot ti-chi-bot added status/LGT2 Indicates that a PR has LGTM 2. and removed status/LGT1 Indicates that a PR has LGTM 1. labels Dec 27, 2021
bb7133
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@zimulala
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PTAL @wjhuang2016 @bb7133

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/merge

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

Commit hash: 7f98a78

@ti-chi-bot ti-chi-bot added the status/can-merge Indicates a PR has been approved by a committer. label Dec 28, 2021
@ti-chi-bot ti-chi-bot merged commit 4ca3b02 into pingcap:master Dec 28, 2021
ti-srebot pushed a commit to ti-srebot/tidb that referenced this pull request Dec 28, 2021
@zimulala @ti-srebot
cherry pick pingcap#31051 to release-5.1
e2666b3 
Signed-off-by: ti-srebot <ti-srebot@pingcap.com>
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cherry pick to release-5.1 in PR #31069

ti-srebot pushed a commit to ti-srebot/tidb that referenced this pull request Dec 28, 2021
@zimulala @ti-srebot
cherry pick pingcap#31051 to release-5.2
8b72b87 
Signed-off-by: ti-srebot <ti-srebot@pingcap.com>
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cherry pick to release-5.2 in PR #31070

ti-srebot pushed a commit to ti-srebot/tidb that referenced this pull request Dec 28, 2021
@zimulala @ti-srebot
cherry pick pingcap#31051 to release-5.3
f4b943a 
Signed-off-by: ti-srebot <ti-srebot@pingcap.com>
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cherry pick to release-5.3 in PR #31071

@zimulala zimulala deleted the zimuxia/ctc-p branch December 28, 2021 06:01
ti-chi-bot pushed a commit that referenced this pull request Feb 22, 2022
@ti-srebot
ddl: fix concurrent column type changes(with changing data) that caus…
ec7d6b3 
…e schema and data inconsistencies (#31051) (#31069)

close #31048
ti-chi-bot pushed a commit that referenced this pull request Feb 22, 2022
@ti-srebot
ddl: fix concurrent column type changes(with changing data) that caus…
912bfea 
…e schema and data inconsistencies (#31051) (#31071)

close #31048
ti-chi-bot pushed a commit that referenced this pull request Apr 12, 2022
@ti-srebot
ddl: fix concurrent column type changes(with changing data) that caus…
ba8e845 
…e schema and data inconsistencies (#31051) (#31070)

close #31048
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@tangenta tangenta tangenta approved these changes

@wjhuang2016 wjhuang2016 wjhuang2016 approved these changes

@AilinKid AilinKid AilinKid approved these changes

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Concurrent Column Type Change would cause inconsistent schema and data
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