schemadiff: DROP COLUMN not eligible for INSTANT algorithm if covered by an index

[shlomi-noach]

Description

Context: #14877
In evaluating whether a DROP COLUMN is eligible to ALGORITHM=INSTANT, we must make sure that the column is not covered by any existing index. If it is, then dropping the column implies modifying the index, which is a non-INSTANT operation in MySQL.

Related Issue(s)

• Feature request: schemadiff to be aware and knowledgeable about INSTANT-capable changes #14877
• schemadiff: using MySQL capabilities to analyze a SchemaDiff and whether changes are applicable instantly/immediately. #14878
• OnlineDDL to use schemadiff version capabilities; refactor some flavor code. #14883

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on 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.

[shlomi-noach]

Might need to update a test, but once it passes I'll merge.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.39%. Comparing base (f118ba2) to head (f908b69).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15714      +/-   ##
==========================================
- Coverage   68.40%   68.39%   -0.01%     
==========================================
  Files        1556     1556              
  Lines      195121   195255     +134     
==========================================
+ Hits       133479   133554      +75     
- Misses      61642    61701      +59     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.