ddl: handle the incorrect number of placement followers

[sylzd]

What problem does this PR solve?

Issue Number: close #30453

Problem Summary:

What is changed and how it works?

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

Limit the maximum size of follower numbers to 8 in placement policies.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• djshow832
• morgo

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[sylzd]

@morgo I am not sure if we should return warning after ddl for these reasons:

1. the check function checkPolicyValidation is used somewhere without session for asynchronous executing such as onCreatePlacementPolicy, we need much redundant code to handle the case.🤣
2. some cases we need odd followers, like follower read, geo partition, and some followers need not participate in vote ...
3. It seems all ddl warning info is returned before ddl executing, and the ddl will not execute actually, such as drop if exists、 create if not exists.

[sylzd]

/run-check_dev_2

[morgo]

@sylzd good points. Let me take a look and make sure we handle these cases correctly.

[djshow832]

Please add a release note to the PR description. Rest LGTM

[AilinKid]

@morgo I am not sure if we should return warning after ddl for these reasons:

1. the check function checkPolicyValidation is used somewhere without session for asynchronous executing such as onCreatePlacementPolicy, we need much redundant code to handle the case.rofl
2. some cases we need odd followers, like follower read, geo partition, and some followers need not participate in vote ...
3. It seems all ddl warning info is returned before ddl executing, and the ddl will not execute actually, such as drop if exists、 create if not exists.

I'm not sure about 2...
but for 1 & 3, ddl background warnings can be fetched into DDLReorgMeta which is designed for reorg type job, maybe we can utilize it if necessary.

[sylzd]

@morgo I am not sure if we should return warning after ddl for these reasons:

1. the check function checkPolicyValidation is used somewhere without session for asynchronous executing such as onCreatePlacementPolicy, we need much redundant code to handle the case.rofl
2. some cases we need odd followers, like follower read, geo partition, and some followers need not participate in vote ...
3. It seems all ddl warning info is returned before ddl executing, and the ddl will not execute actually, such as drop if exists、 create if not exists.

I'm not sure about 2... but for 1 & 3, ddl background warnings can be fetched into DDLReorgMeta which is designed for reorg type job, maybe we can utilize it if necessary.

LGTM~ that helps~ I will take the advice from you if we are sure to append a warning here.(For 2... maybe a note level warning is not bad!) but I still have some questions: 🤣

1. How do we generally define the error code that does not exist in MySQL? like 8XXX?
2. how can we avoid duplicated warning append? we check the validation twice, and I do not find a similar case about warnings.

[morgo]

1. How do we generally define the error code that does not exist in MySQL? like 8XXX?

Yes exactly. MySQL error codes are far from this range, so it is safe to use.

2. how can we avoid duplicated warning append? we check the validation twice, and I do not find a similar case about warnings.

There is no builtin support. You can use vars.StmtCtx.GetWarnings() to get the warnings and vars.StmtCtx.SetWarnings(warns) to set the warnings if you need to implement a function for this.

[morgo]

For (2) we might need to skip this rule for now. It is fine without it. This PR LGTM.

[morgo]

/merge

[ti-chi-bot]

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

Commit hash: 21ed19d

[ti-chi-bot]

@sylzd: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.