mounter(ticdc): fix mounter default value panic and data inconsistency

[maxshuang]

close #3929 #3918

What problem does this PR solve?

When meet "amend + add column datetime default '2020-10-10 10:10:10' (DDL)", TiCDC will

1. panic, as the default value type is not consistent with column type
2. data inconsistence

What is changed and how it works?

1. Don't format default value in column meta data
2. Check default value exist before check not null flag

Check List

Tests

• Unit test
• Manual test (add detailed scripts or steps below)
  Start 2 transactions:

1. Transaction 1:

Create table test_column(id int primary key);
Insert Into test_column values(1);
begin;
Insert Into test_column values(2);
// hold the trx untill Transaction 2 commit DDL
commit;

• Transaction 2:

alter table test_column add column c0 datetime default "2020-10-10 10:10:10";

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation
• Need to update key monitor metrics in both TiCDC document and official document

Release note

Fix column default value panic and data inconsistency

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• amyangfei
• overvenus

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[codecov-commenter]

Codecov Report

Merging #3930 (6425483) into master (3873d39) will decrease coverage by 1.9478%.
The diff coverage is 67.3486%.

Flag	Coverage Δ
cdc	58.5789% <67.3486%> (+0.3423%)	⬆️
dm	52.2214% <ø> (-3.8132%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

@@               Coverage Diff                @@
##             master      #3930        +/-   ##
================================================
- Coverage   57.0741%   55.1263%   -1.9479%     
================================================
  Files           478        486         +8     
  Lines         56551      59848      +3297     
================================================
+ Hits          32276      32992       +716     
- Misses        20978      23506      +2528     
- Partials       3297       3350        +53     

[overvenus]

Could you add a unit test?

[maxshuang]

Could you add a unit test?

Sure, I will do it later. So I hold the pr.

[maxshuang]

/run-dm-compatibility-test
/run-dm-integration-test
/run-integration-test
/run-kafka-integration-test

[maxshuang]

/run-verify

[maxshuang]

/run-kafka-integration-test
/run-integration-test
/run-dm-compatibility-test
/run-dm-integration-test

[overvenus]

Rest LGTM

[maxshuang]

/run-kafka-integration-test /tidb=pr/30773
/run-integration-tests /tidb=pr/30773

[maxshuang]

/run-dm-compatibility-test
/run-dm-integration-test

[amyangfei]

What will happen in this scenario?

[maxshuang]

sink null to the downstream and cause data inconsistency for unsupported data type

[maxshuang]

/run-kafka-integration-test /tidb=pr/30773
/run-integration-tests /tidb=pr/30773
/run-dm-compatibility-test
/run-dm-integration-test

[overvenus]

LGTM

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #4442.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #4443.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #4444.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #4445.

[ti-chi-bot]

In response to a cherrypick label: new pull request could not be created: failed to create pull request against pingcap/tiflow#release-5.3 from head ti-chi-bot:cherry-pick-3930-to-release-5.3: the GitHub API request returns a 403 error: {"message":"You have exceeded a secondary rate limit and have been temporarily blocked from content creation. Please retry your request again later.","documentation_url":"https://docs.github.com/rest/overview/resources-in-the-rest-api#secondary-rate-limits"}