sink, sorter: do not hog memory (#2606)

[ti-chi-bot]

This is an automated cherry-pick of #2606

What problem does this PR solve?

Reduce memory usage for sink node and file backend.

Cc https://github.com/pingcap/ticdc/issues/2553

Check List

Tests

• Manual test (add detailed scripts or steps below)

Related changes

• Need to cherry-pick to the release branch

Release note

None

[ti-chi-bot]

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[overvenus]

/merge

[ti-chi-bot]

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

Commit hash: 5fe4f3f

[amyangfei]

/run-integration-tests
/run-kafka-tests

[amyangfei]

/merge

[amyangfei]

/run-integration-tests
/run-kafka-tests

[amyangfei]

/run-integration-tests
/run-kafka-tests

[amyangfei]

/merge

[ti-chi-bot]

@ti-chi-bot: Your PR was out of date, I have automatically updated it for you.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.

[amyangfei]

/run-integration-tests
/run-kafka-tests

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (release-5.1@d7430c2). Click here to learn what that means.
The diff coverage is n/a.

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