*: tiny refactor code to reduce txn conflict on 'table_cache_meta'

[tiancaiamao]

What problem does this PR solve?

Issue Number: close #32386

Problem Summary:

The warning log is caused by the fact that "select ... for update" can't retry when using optimistic transaction.

What is changed and how it works?

Tiny code refactor. Two changes mainly:

• Remove 'for update', just use the non-'for update' statement

There is no need to worry about write skew abnormity here, we can just use the default RR (SI)

• Refactor the renew lease code

In the past, I make a goroutine along with a channel for the renew lease operation,
i.e. send the renew operation (func) teller the worker to execute it.

type renewLeaseCh chan func()
go do.renewLease()

func (do *Domain) renewLease() {
	defer func() {
		do.wg.Done()
		logutil.BgLogger().Info("renew lease goroutine exited.")
	}()
	for {
		select {
		case <-do.exit:
			close(do.renewLeaseCh)
			return
		case op := <-do.renewLeaseCh:
			op()
		}
	}
}

And this pattern to avoid duplicated message: https://github.com/pingcap/tidb/pull/31475/files

This is complex than it should be.

To avoid duplicated message, a chan(1) can be used as a token limiter, and spawn a new goroutine is handy:

c.renewReadLease = make(chan struct{}, 1)

select {
case c.renewReadLease <- struct{}{}:
	go c.renewLease(ts, data, leaseDuration)
default:
}

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Tiny refactor

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

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lcwangchao
• tangenta

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.

[tiancaiamao]

/run-unit-test

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/5fcb24b1e353badad2cc17b94db3352f97963612

[tiancaiamao]

Ref #25293

[tangenta]

Please make sure this is expected:

Previously each domain can have at most 10 goroutines for renewing lease. After this PR, each cached table in infoSchema can spawn a new goroutine to renew lease.

[tiancaiamao]

Please make sure this is expected:

Previously each domain can have at most 10 goroutines for renewing lease. After this PR, each cached table in infoSchema can spawn a new goroutine to renew lease.

This is by design.
In the old code, there will be duplicated renew lease operation, because there are 10 background goroutines, they can handle several message simultaneously.
Now there will be only one active goroutine.

[lcwangchao]

It seems to be a semaphore, why not just use semaphore in go lib?

[tiancaiamao]

I'm not familiar with semaphore, the channel is more simple for me here.

[tiancaiamao]

/merge

[ti-chi-bot]

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

Commit hash: bb591be

[ti-chi-bot]

@tiancaiamao: 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.

[tiancaiamao]

/run-unit-test

[tiancaiamao]

/run-mysql-test