Workflow Status: change logic to determine whether MoveTables writes are switched

[rohit-nayak-ps]

Description

We use the table routing rules to decide where reads and writes are routed for tables which are part of MoveTables workflows.

For each table we have rules like

t1 => source.t1 
source.t1 => source.t1
t1@replica => source.t1@replica
source.t1@replica => source.t1@replica
target.t1 => source.t1

when no traffic is switched, or when all traffic is switched:

t1 => target.t1 
source.t1 => target.t1
t1@replica => target.t1@replica
source.t1@replica => target.t1@replica
target.t1 => target.t1

To determine whether writes are switched, we check the route for t1. If it is pointing to target it is considered that writes have been switched.

The problem comes the same table exists in different source keyspaces. For example if there are two workflows one from source1=>target1 and another from source2=>target2, both with a table t1.

Now if one workflow's writes are switched we end up with the route for t1 pointing to target1.t1. When the next workflow's writes are switched we now overwrite that rule so that it points to target2.t1. The logic now assumes writes for the first workflow have not been switched.

Fix:
In general, global routing rules don't make sense in such cases. But as an initial quick fix we change the logic to looking at the source.t1 key instead of t1. In our case then after the two workflows have been switched we will get source1.t1 => target1.t1 and source2.t1 => target2.t1, resulting in the right state being deduced.

We do the same for for replica/rdonly types as well.

Related Issue(s)

• Fixes: MoveTables: Vitess infers the read and write routes incorrectly if the same table is involved in multiple workflows #16733

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

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[codecov]

Codecov Report

Attention: Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.

Project coverage is 68.92%. Comparing base (538dd4c) to head (a847429).
Report is 88 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtctl/workflow/server.go	77.77%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16731      +/-   ##
==========================================
- Coverage   68.98%   68.92%   -0.06%     
==========================================
  Files        1562     1565       +3     
  Lines      200690   201748    +1058     
==========================================
+ Hits       138449   139058     +609     
- Misses      62241    62690     +449     

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[mattlord]

We can calculate this key once. That's more efficient and prevents any accidental drift.

[mattlord]

Is this really usable outside of this file and its test? If not, better IMO to include it in the test (can be a func var).