VReplication: Address SwitchTraffic bugs around replication lag and cancel on error

[mattlord]

Description

This PR improves the error handling for cancel failures (see issue). When the context changes are commented out in the PR branch we can see the new error handling in action here when using the manual test in the issue:

❯ vtctldclient MoveTables --workflow commerce2customer --target-keyspace customer switchtraffic
E0123 10:57:24.082537   40795 main.go:60] rpc error: code = Unknown desc = failed to sync up replication between the source and target: rpc error: code = DeadlineExceeded desc = context deadline exceeded

could not revert denied tables / shard access: Code: INTERNAL
keyspace commerce is not locked (no locksInfo)

cancel migration failed, manual cleanup work may be necessary

And with the context changes in place:

❯ vtctldclient MoveTables --workflow commerce2customer --target-keyspace customer switchtraffic
E0123 11:28:24.848992   80414 main.go:60] rpc error: code = Unknown desc = failed to sync up replication between the source and target: rpc error: code = DeadlineExceeded desc = context deadline exceeded

This PR also addresses the inaccuracy of the max_v_replication_transaction_lag value as noted in the issue. After adjusting this calculation, the manual test now fails in the canSwitch() pre-check as expected:

...
vtctldclient MoveTables --workflow commerce2customer --target-keyspace customer switchtraffic
E0123 13:09:33.292425    7651 main.go:60] rpc error: code = Unknown desc = cannot switch traffic for workflow commerce2customer at this time: replication lag 84s is higher than allowed lag 30s

And when monitoring the lag as the test runs you can see it correctly measured when there is little to no lag, you can see it increase as the actual lag increases, and then see it go back down (it is NOT included in the output when the value is 0):

❯ while true; do vtctldclient GetWorkflows customer --compact --include-logs=false | grep max_v_replication_transaction_lag; sleep 1; done
...
      "max_v_replication_transaction_lag": "1",
      "max_v_replication_transaction_lag": "1",
      "max_v_replication_transaction_lag": "2",
      "max_v_replication_transaction_lag": "1",
...
      "max_v_replication_transaction_lag": "84",
      "max_v_replication_transaction_lag": "85",
      "max_v_replication_transaction_lag": "86",
      "max_v_replication_transaction_lag": "87",
      "max_v_replication_transaction_lag": "73",
      "max_v_replication_transaction_lag": "74",
      "max_v_replication_transaction_lag": "75",
...
      "max_v_replication_transaction_lag": "93",
      "max_v_replication_transaction_lag": "94",
      "max_v_replication_transaction_lag": "1",
      "max_v_replication_transaction_lag": "1",
      "max_v_replication_transaction_lag": "1",
      "max_v_replication_transaction_lag": "1",

Note

I think that we should backport this all the way to v19 as you cannot successfully revert a failed traffic switch in v19+ due to the changes in #17340
Of course the real issue was the testing gap, which was also closed in this PR.

Related Issue(s)

• Fixes: Bug Report: VReplication SwitchTraffic cancel fails due to not having topo locks #17620

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 50.00000% with 52 lines in your changes missing coverage. Please review.

Project coverage is 67.63%. Comparing base (99856a2) to head (2253a88).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtctl/workflow/traffic_switcher.go	25.00%	21 Missing ⚠️
go/vt/vtctl/workflow/server.go	42.85%	16 Missing ⚠️
go/vt/vtctl/workflow/workflows.go	81.81%	6 Missing ⚠️
go/vt/vtctl/workflow/stream_migrator.go	54.54%	5 Missing ⚠️
go/vt/vtctl/workflow/switcher.go	0.00%	2 Missing ⚠️
go/vt/vtctl/workflow/switcher_dry_run.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17616      +/-   ##
==========================================
- Coverage   67.69%   67.63%   -0.06%     
==========================================
  Files        1586     1586              
  Lines      255403   255666     +263     
==========================================
+ Hits       172883   172911      +28     
- Misses      82520    82755     +235     

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[mattlord]

This was another bug in our cancel path that was highlighted by the new test (specifically by trying to query the table after the failed switch).