`ScatterRegions` not returning which region(s) are failed to scatter

[D3Hunter]

Bug Report

What did you do?

ScatterRegions not returning which region(s) are failed to scatter. br/lightning now will prefer ScatterRegions to do region scatter for performance reason, but if some regions failed to scatter for reasons like region %d is not fully replicated, it will also return success and only give a percentage of success regions, but doesn't tell client which failed. currently br/lightning will take this as success, and will move on, and cause region/data skew.

br/lightning have retry on scatter, but need PD returns which regions have failed

pd/pkg/mcs/scheduling/server/grpc_service.go

Lines 219 to 232 in 2bbeb9c

	if len(failures) > 0 {
	percentage = 100 - 100*len(failures)/(opsCount+len(failures))
	log.Debug("scatter regions", zap.Errors("failures", func() []error {
	r := make([]error, 0, len(failures))
	for _, err := range failures {
	r = append(r, err)
	}
	return r
	}()))
	}
	return &schedulingpb.ScatterRegionsResponse{
	Header: wrapHeader(),
	FinishedPercentage: uint64(percentage),
	}, nil

What did you expect to see?

What did you see instead?

What version of PD are you using (pd-server -V)?