Improve efficiency of vtorc topo calls

[timvaillancourt]

Description

This PR adds a similar optimization to this PR to vtorc by moving to using ts.GetTabletsByCell(...) and the new ts.GetTabletsByShard(...) methods to fetch tablets. These methods respect the concurrency limit flag for the topo and seem to be more efficient overall

Support for filtering by keyspace/shard was added to ts.GetTabletsByCell(...) which is called by ts.GetTabletsByShard(...)

Related to this discussion, we're unfortunately forced to fetch "all" records from the cell just to filter them out by keyspace/shard using x != y. In our production when fetching topo records for a single shard, < 0.5% of the topo records fetched are actually used - but that's nothing new

Related Issue(s)

Resolves #17073

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 15.94203% with 58 lines in your changes missing coverage. Please review.

Project coverage is 67.41%. Comparing base (fa5a2c5) to head (707ad06).
Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/topo/shard.go	0.00%	54 Missing ⚠️
go/vt/vtorc/logic/tablet_discovery.go	0.00%	3 Missing ⚠️
go/vt/topo/tablet.go	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17071      +/-   ##
==========================================
+ Coverage   67.17%   67.41%   +0.23%     
==========================================
  Files        1571     1569       -2     
  Lines      252246   252171      -75     
==========================================
+ Hits       169458   170002     +544     
+ Misses      82788    82169     -619     

☔ View full report in Codecov by Sentry.
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[mattlord]

This is looking good! ❤️ I only had some minor nits and suggestions. Let me know what you think.

[GuptaManan100]

Apart from Matt's comments, everything else LGTM. It can be merged once they have been addressed.

[timvaillancourt]

Thanks for the review! Updated with @mattlord's suggestions 👍

[mattlord]

Looking good! The only remaining issue is whether or not we want to support filtering by shard w/o a keyspace. I'm OK either way, but if we do want to support that then we should add a test case for it. That make sense?

[timvaillancourt]

The only remaining issue is whether or not we want to support filtering by shard w/o a keyspace

@mattlord I don't plan to support this because I can't think of a use case. I've updated to make keyspace required 👍

[mattlord]

Looks like the new unit test is flaky:

• https://github.com/vitessio/vitess/actions/runs/11691174276/attempts/1?pr=17071
• https://github.com/vitessio/vitess/actions/runs/11691174293/attempts/1?pr=17071

That's the only thing left! Thank you for sticking this out, @timvaillancourt ! This will be a nice improvement.

[timvaillancourt]

Hmm, this flakiness is weird. Perhaps I need to sort the tt.expectedTablets but I thought that wasn't necessary 🤔

[timvaillancourt]

@mattlord I believe moving tt.keyspaceShards to keyspaceShards []*topo.KeyspaceShard (from a map) will fix this flakiness 👍

[mattlord]

Great work on this, @timvaillancourt ! You can merge any time, just please don't forget to squash and merge.

One last note, up to you if you want to add it:

			slices.SortFunc(out, func(i, j *topo.TabletInfo) int {
				return cmp.Compare(i.Alias.Uid, j.Alias.Uid)
			})
			for i, tablet := range out {
				expected := tt.expectedTablets[i]
				require.Equal(t, expected.Alias.String(), tablet.Alias.String())
				require.Equal(t, expected.Keyspace, tablet.Keyspace)
				require.Equal(t, expected.Shard, tablet.Shard)
			}

Right now you're ordering all of the entries in expectedTablets by Uid in the test cases. IMO it's worth sorting that slice as well so that things do not become flaky in the future if someone modifies the existing test cases or adds new ones where that slice is not ordered:

			slices.SortFunc(out, func(i, j *topo.TabletInfo) int {
				return cmp.Compare(i.Alias.Uid, j.Alias.Uid)
			})
			slices.SortFunc(tt.expectedTablets, func(i, j *topo.TabletInfo) int {
				return cmp.Compare(i.Alias.Uid, j.Alias.Uid)
			})
			for i, tablet := range out {
				expected := tt.expectedTablets[i]
				require.Equal(t, expected.Alias.String(), tablet.Alias.String())
				require.Equal(t, expected.Keyspace, tablet.Keyspace)
				require.Equal(t, expected.Shard, tablet.Shard)
			}

[timvaillancourt]

@mattlord thanks for the reviews, added that!