Refactor Server.LookupVindexCreate

[beingnoble03]

Description

This PR is based on #17092. Mainly refactors prepareCreateLookup().

Related Issue(s)

• Tracking Issue: vtctldclient/vtctld: Enhance test coverage and code refactor  #16499

Checklist

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[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 50 lines in your changes missing coverage. Please review.

Project coverage is 67.60%. Comparing base (45192d2) to head (4e8a539).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtctl/workflow/lookup_vindex.go	88.28%	45 Missing ⚠️
go/vt/vtctl/workflow/server.go	68.75%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17242      +/-   ##
==========================================
+ Coverage   67.52%   67.60%   +0.07%     
==========================================
  Files        1581     1582       +1     
  Lines      253948   253985      +37     
==========================================
+ Hits       171480   171706     +226     
+ Misses      82468    82279     -189     

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[mattlord]

This is a new struct that has a subset of the workflow server's values, and it's not specific to lookup vindexes at all. Can you help me understand what value this provides?

The workflow server type being:

type Server struct {
	ts  *topo.Server
	tmc tmclient.TabletManagerClient
	// Limit the number of concurrent background goroutines if needed.
	sem     *semaphore.Weighted
	env     *vtenv.Environment
	options serverOptions
}

Otherwise this LGTM. Thanks!

[beingnoble03]

Sure, the idea for defining lookup struct was to differentiate the helper functions related to LookupVindex from Server (as of now lookup just differentiates LookupVindexCreate helper functions in this PR), this is similar to what was done in #17092 by defining workflowFetcher. We can always include more functions (related to lookup vindexes) in follow-ups. Please let me know if you think this can be improved further. Thanks for the review!

[mattlord]

OK, so I take that to mean this is really for a human reader/developer to try and make the code easier to reason about and manage as lookup vindex related workflow code is in its own specific file and has its own specific method receiver.

In that case, IMO we should do this:

1. Go from workflow/lookup.go to workflow/lookup_vindex.go
2. Go from workflow.lookup.prepareCreateLookup to workflow.lookupVindex.prepareCreate (the type becomes lookupVindex and we don't need that lookupvindex context in the function name as its encapsulated in the receiver type

Lookup is a very generic term and it's not otherwise obvious to me how it adds distinction, separation, discoverability, and clarity specifically around the VReplication backfilling work for Lookup Vindexes via the LookupVindex client command and related RPCs. A lookup vindex is a specific concept in Vitess, and the client command we're processing in the workflow server is LookupVindex (also here and here). Otherwise I would think that workflow/lookup was about code related to looking up workflows. Does this all make sense?

Thanks!

[beingnoble03]

that does make a lot of sense, improves the readability. thank you so much @mattlord!

pushed the changes, please have a look.

[mattlord]

LGTM. Thanks again, @beingnoble03 !

[mattlord]

Nit, we didn't update the struct name in the comment.

[beingnoble03]

Oh sorry! Pushed the change now.