Introducing ExecuteMultiFetchAsDba gRPC and vtctldclient ExecuteMultiFetchAsDBA command

[shlomi-noach]

Description

See #15505 for context. This PR adds:

• ExecuteMultiFetchAsDba gRPC call, with ExecuteMultiFetchAsDbaRequest and ExecuteMultiFetchAsDbaResponse proto messages.
• vtctldclient ExecuteMultiFetchAsDBA command, which acts very similarly to ExecuteFetchAsDBA, except it returns a list of results (seen in --json as an array of results).

The behavior of ExecuteFetchAsDBA in rpc_query.go remains unchanged, although we consolidate its logic with the new
ExecuteMultiFetchAsDBA implementation.

The main changes of this PR are in go/vt/vttablet/tabletmanager/rpc_query.go and in go/cmd/vtctldclient/command/query.go. The rest is gRPC/interface boilerplate and testing.

Docs: vitessio/website#1709

No backport required.

Related Issue(s)

• Tracking: introduce ExecuteMultiFetchAsDba gRPC method #15505
• Prior work: Protect ExecuteFetchAsDBA against multi-statements, excluding a sequence of CREATE TABLE|VIEW. #14954

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 35.00000% with 117 lines in your changes are missing coverage. Please review.

Project coverage is 65.61%. Comparing base (696fe0e) to head (fdabcfb).
Report is 119 commits behind head on main.

Files	Patch %	Lines
go/cmd/vtctldclient/command/query.go	14.70%	29 Missing ⚠️
go/vt/vttablet/grpctmclient/client.go	0.00%	25 Missing ⚠️
go/vt/vttablet/tabletmanager/rpc_query.go	64.00%	18 Missing ⚠️
go/vt/wrangler/tablet.go	0.00%	11 Missing ⚠️
go/vt/vttablet/grpctmserver/server.go	0.00%	9 Missing ⚠️
go/vt/vttablet/tmrpctest/test_tm_rpc.go	0.00%	8 Missing ⚠️
...t/vtctl/grpcvtctldserver/testutil/test_tmclient.go	46.15%	7 Missing ⚠️
go/vt/vtctl/grpcvtctldclient/client_gen.go	0.00%	4 Missing ⚠️
go/vt/vtcombo/tablet_map.go	0.00%	2 Missing ⚠️
go/vt/vtctl/localvtctldclient/client_gen.go	0.00%	2 Missing ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15506      +/-   ##
==========================================
- Coverage   67.41%   65.61%   -1.81%     
==========================================
  Files        1560     1563       +3     
  Lines      192752   194638    +1886     
==========================================
- Hits       129952   127703    -2249     
- Misses      62800    66935    +4135     

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[dbussink]

For symmetry with the other ExecuteFetch, does this mean we also want / need ExecuteMultiFetchAsApp?

[shlomi-noach]

I'm not sure. We have a specific use case for DBA, and no specific use case for App, so unsure we should add just for the sake of symmetry.

[dbussink]

@shlomi-noach My thinking is that it would be mostly for people using ExecuteFetchAsApp with multiple queries and have it kinda accidentally mostly work. They wouldn't have anywhere to go if we don't have it. I don't know if this is a real valid concern though or not.

[shlomi-noach]

Having consulted with the team, we should not add ExecuteMultiFetchAsApp right now. Only when there's a specific use case.

[shlomi-noach]

Docs PR: vitessio/website#1709