Online DDL cutover enhancements

[shlomi-noach]

Description

Several enhancements to the Online DDL cut-over logic:

• With forced cut-over, we now kill queries and transactions holding onto locks on migrated table, not only before the cut-over, but also while the RENAME is being applied. Without this, there's a race condition where a long running query could start running just after queries are killed and right before the RENAME starts running.
  When killing queries & transactions, we skip the connection IDs of the cut-over related queries themselves.
• Sanitized and reduced query and lock timeouts during the cut-over. There were some excessive timeouts, notably an overlooked 5*onlineDDL.CutOverThreshold*4 value which evaluates to 5min on a 15s timeout.
• Improved logging to always include migration UUID.
• When --force-cut-over-after value is <= 1ms we consider it as "immediate" even if we somehow measure the time-since-ready to be less than that.

Related Issue(s)

• Folow up to Online DDL forced cut-over: terminate transactions holding metadata locks on table #17535
• Feature Request: Online DDL cut-over backoff + forced completion #14530

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

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[codecov]

Codecov Report

Attention: Patch coverage is 11.36364% with 39 lines in your changes missing coverage. Please review.

Project coverage is 67.49%. Comparing base (826d78d) to head (b1f59c5).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vttablet/onlineddl/executor.go	11.36%	39 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18423      +/-   ##
==========================================
- Coverage   67.51%   67.49%   -0.02%     
==========================================
  Files        1607     1607              
  Lines      262706   262768      +62     
==========================================
- Hits       177370   177360      -10     
- Misses      85336    85408      +72     

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[Copilot]

Pull Request Overview

This PR enhances the Online DDL cut-over by killing queries during the RENAME phase, tightening cut-over timeouts, improving logging with migration UUIDs, and treating very small force-cut-over thresholds as immediate.

• Extend killTableLockHoldersAndAccessors to accept excluded connection IDs and include UUID in logs
• Reduce excessive lock-wait timeouts and simplify force-cut-over logic for “immediate” thresholds
• Update tests to cover new force-cut-over behavior and fix test names

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
executor_test.go	Renamed and added test cases for force-cut-over threshold logic
executor.go	Added UUID to kill logic, skip exclusions, refined timeouts, and adjusted context cancellation during rename

Comments suppressed due to low confidence (1)

go/vt/vttablet/onlineddl/executor_test.go:137

• [nitpick] The test name is ambiguous: it refers to "microsecond" but the threshold is 1ms. Consider renaming to clarify that force-cut-over at or below 1ms is immediate.

			name:                     "microsecond, ready irrespective of sinceReadyToComplete",