Support SHOW VITESS_MIGRATIONS from inside a transaction

[shlomi-noach]

Description

See story in #16242

Related Issue(s)

Fixes #16242

Checklist

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Deployment Notes

[vitess-bot]

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[systay]

Could we add an end-to-end test that checks this issue?

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 68.68%. Comparing base (66bf89b) to head (92c5aeb).
Report is 6 commits behind head on main.

Files	Patch %	Lines
go/vt/vttablet/tabletserver/query_executor.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16399      +/-   ##
==========================================
+ Coverage   68.66%   68.68%   +0.02%     
==========================================
  Files        1548     1548              
  Lines      199084   199092       +8     
==========================================
+ Hits       136699   136753      +54     
+ Misses      62385    62339      -46     

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[shlomi-noach]

Could we add an end-to-end test that checks this issue?

Added!

[timvaillancourt]

@shlomi-noach is conn *StatefulConnection meant to be used here? I don't follow this part

[shlomi-noach]

Yes-ish :). I'm not all too familiar with this either, but I got guidance from @harshit-gangal. The StatefulConnection is the standard way for you to implement a transactional behavior working with QueryService. So we should pass that variable. Normally I'd also use the variable -- except:

• I don't really require show vitess_migrations to exhibit transactional behavior; it's a show command and I don;t need it to e.g. be repeatable-read or anything. I only need it to work from within a transaction.
• Therefore no need to bloat the transaction.
• Also, the existing logic uses the executor's own connection pooling, which is fine, and there's no need/reason to now take apart the existing and working mechanism within the executor to accommodate the transactional connection.

[timvaillancourt]

Ok sounds good 👍