reduce NOWAIT usage to tables with unique keys for foreign key plans

[harshit-gangal]

Description

This PR limits the usage of NOWAIT to tables having unique key columns.
NOWAIT leads to an error when acquiring the required index lock and it cannot be granted immediately. This leads to the failure of DML execution for foreign key cases.
This is only required when the table has unique keys. When a table has unique keys MySQL does not take gap locks resulting in the issue described in #14532

Related Issue(s)

• RFC: Foreign Key Support in Vitess #12967

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[arthurschreiber]

@harshit-gangal Would you mind extending the PR description to explain why we want to use NOWAIT only on a subset of foreign key plans? Just curious what this change actually means.

[harshit-gangal]

@harshit-gangal Would you mind extending the PR description to explain why we want to use NOWAIT only on a subset of foreign key plans? Just curious what this change actually means.

updated the description.

[GuptaManan100]

Have you run the foreign key fuzzer for a longer duration locally to make sure this doesn't cause any correctness issues?

[harshit-gangal]

Have you run the foreign key fuzzer for a longer duration locally to make sure this doesn't cause any correctness issues?

Yes I did :)