Filter by keyspace earlier in tabletgateways WaitForTablets(...)

[timvaillancourt]

Description

This PR causes the tabletgateway .WaitForTablets(...) method to filter targets by keyspace (set by --keyspaces_to_watch) earlier in the process

Currently, the logic under .WaitForTablets(...):

1. Uses srvtopo.FindAllTargets(...) to fetch the targets by-cell for any keyspace (even if --keyspaces_to_watch is set)
   • This calls .GetSrvKeyspace(...) on the toposerver for every keyspace in goroutines w/wait group
2. Later targets that do not match --keyspaces_to_watch are removed from targets []*querypb.Target

Instead this PR implements the filtering in srvtopo.FindAllTargets(...) by not-fetching keyspaces from the topo that will just get filtered anyways. This can avoid topo calls and unnecessary filtering of results on deployments with many keyspaces and a subset of keyspaces set as --keyspaces_to_watch

The changed codepath and signatures are only called by vtgate/tabletgateway so this change had a limited impact

Related Issue(s)

• Fixes: Feature Request: reduce topo calls in tabletgateway's WaitForTablets(...) #15373

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

[vitess-bot]

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[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 65.43%. Comparing base (d8f771c) to head (612d8c4).
Report is 9 commits behind head on main.

Files	Patch %	Lines
go/vt/srvtopo/discover.go	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15347      +/-   ##
==========================================
+ Coverage   65.39%   65.43%   +0.03%     
==========================================
  Files        1561     1561              
  Lines      193524   193630     +106     
==========================================
+ Hits       126563   126696     +133     
+ Misses      66961    66934      -27     

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[mattlord]

LGTM! I only had a few very minor comments/nits. Let me know what you think and I can come back to this quickly and help to get it merged.

Thanks, @timvaillancourt !

[mattlord]

@timvaillancourt do you mind creating a real quick issue as well for this? 🙏

[timvaillancourt]

LGTM! I only had a few very minor comments/nits. Let me know what you think and I can come back to this quickly and help to get it merged.

@mattlord no problem, I try to imitate the style of the project I'm committing to so this is good knowledge 👍

An issue is created here: #15373

[mattlord]

Thanks, @timvaillancourt ! ❤️

[deepthi]

Nice work! I'm loving these little optimizations that y'all have been doing.