parser: use Unique to save memory in the CIstr [WIP]

[hawkingrei]

What problem does this PR solve?

Issue Number: close #xxx

Problem Summary:

What changed and how does it work?

Check List

Tests

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

  • I checked and no code files have been changed.

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

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[FORMAT CHECKER NOTIFICATION]

Notice: To remove the do-not-merge/needs-linked-issue label, please provide the linked issue number on one line in the PR body, for example: Issue Number: close #123 or Issue Number: ref #456.

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Tests

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

_{📖 For more info, you can check the "Contribute Code" section in the development guide.}

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please ask for approval from hawkingrei and additionally assign benmeadowcroft, bornchanger, gmhdbjd, zanmato1984 for approval(Please ensuring that each of them provides their approval before proceeding). For more information see the Code Review Process.

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[tiprow]

@hawkingrei: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
tidb_parser_test	a3931c9	link	true	/test tidb_parser_test
fast_test_tiprow	a3931c9	link	true	/test fast_test_tiprow

Full PR test history. Your PR dashboard.

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[ti-chi-bot]

@hawkingrei: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/check_dev_2	a3931c9	link	true	/test check-dev2
pull-unit-test-ddlv1	a3931c9	link	true	/test pull-unit-test-ddlv1
idc-jenkins-ci-tidb/unit-test	a3931c9	link	true	/test unit-test
pull-integration-ddl-test	a3931c9	link	true	/test pull-integration-ddl-test
idc-jenkins-ci-tidb/build	a3931c9	link	true	/test build
idc-jenkins-ci-tidb/check_dev	a3931c9	link	true	/test check-dev
pull-br-integration-test	a3931c9	link	true	/test pull-br-integration-test
pull-integration-e2e-test	a3931c9	link	true	/test pull-integration-e2e-test
pull-mysql-client-test	a3931c9	link	true	/test pull-mysql-client-test
idc-jenkins-ci-tidb/mysql-test	a3931c9	link	true	/test mysql-test

Full PR test history. Your PR dashboard.

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 kubernetes-sigs/prow repository. I understand the commands that are listed here.