Performance improvements for UNION

[systay]

Description

This PR introduces a new engine primitive - simple-concatenate, that should be used when we have full type information. In these situations we can do the type aggregation at plan time and plan the coercion of columns when needed, instead of having to do this at runtime. If we do it at runtime, we have to block until all sources have returned at least one chunk of data, and that is slow.

I also changed the concatenate primitive to only do the type calculation once per plan, instead of every time it runs. The first time we use a slow sequential execution, but we store the type info so that future uses of the plan can happen fast.

Our goal is to streamline the concatenate operation, making it faster and more resource-efficient across various use cases.

Related Issue(s)

Related to: #15466

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

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[codecov]

Codecov Report

Attention: Patch coverage is 24.33460% with 199 lines in your changes are missing coverage. Please review.

Project coverage is 65.66%. Comparing base (696fe0e) to head (661fe19).
Report is 272 commits behind head on main.

❗ Current head 661fe19 differs from pull request most recent head 725ed0b. Consider uploading reports for the commit 725ed0b to get more accurate results

Files	Patch %	Lines
go/vt/vtgate/engine/simple_concatenate.go	5.08%	112 Missing ⚠️
go/vt/vtgate/engine/coerce.go	0.00%	71 Missing ⚠️
go/vt/vtgate/planbuilder/operator_transformers.go	83.33%	11 Missing ⚠️
go/vt/vtgate/planbuilder/filter.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15497      +/-   ##
==========================================
- Coverage   67.41%   65.66%   -1.76%     
==========================================
  Files        1560     1564       +4     
  Lines      192752   194693    +1941     
==========================================
- Hits       129952   127837    -2115     
- Misses      62800    66856    +4056     

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[vmg]

very neat. so what would it take now to remove the old concatenate? where is it actually used?

[vitess-bot]

Hello! 👋

This Pull Request is now handled by arewefastyet. The current HEAD and future commits will be benchmarked.

You can find the performance comparison on the arewefastyet website.

[GrahamCampbell]

Is this aiming for the 19.0.2 release?

[github-actions]

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If no action is taken within 7 days, this PR will be closed.

[systay]

let's re-open when we have time