kvclient(cdc): remove rate limiter for scanning and error handling

[hicqu]

What problem does this PR solve?

Issue Number: close #8858

What is changed and how it works?

Remove rate limiter for scanning and error handling.

Check List

Tests

• Manual test:

Questions

Will it cause performance regression or break compatibility?

I have testing it with 4 TiKV instances and 85K regions on every TiKV instance. Here is the result:

• When one TiKV node fails, it can increases TiCDC CPU usage from 300% to 400%;
• PD CPU usage increases from 100% to 145%;

We can see CPU usage doesn't increase too much. So I think the patch is helpful.

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• asddongmen
• nongfushanquan

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[hicqu]

/merge

[ti-chi-bot]

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

Commit hash: f32154d

[hicqu]

/run-verify

[hicqu]

/test verify

[ti-chi-bot]

@hicqu: Your PR was out of date, I have automatically updated it for you.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

trigger some heavy tests which will not run always when PR updated.

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.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #8897.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #8899.