The limit of scatter range scheduler is not right

[rleungx]

Bug Report

pd/server/schedulers/scatter_range.go

Lines 195 to 225 in ca53ac6

	func (l *scatterRangeScheduler) IsScheduleAllowed(cluster opt.Cluster) bool {
	return l.OpController.OperatorCount(operator.OpRange) < cluster.GetOpts().GetRegionScheduleLimit()
	}
	func (l *scatterRangeScheduler) Schedule(cluster opt.Cluster) []*operator.Operator {
	schedulerCounter.WithLabelValues(l.GetName(), "schedule").Inc()
	// isolate a new cluster according to the key range
	c := schedule.GenRangeCluster(cluster, l.config.GetStartKey(), l.config.GetEndKey())
	c.SetTolerantSizeRatio(2)
	ops := l.balanceLeader.Schedule(c)
	if len(ops) > 0 {
	ops[0].SetDesc(fmt.Sprintf("scatter-range-leader-%s", l.config.RangeName))
	ops[0].AttachKind(operator.OpRange)
	ops[0].Counters = append(ops[0].Counters,
	schedulerCounter.WithLabelValues(l.GetName(), "new-operator"),
	schedulerCounter.WithLabelValues(l.GetName(), "new-leader-operator"))
	return ops
	}
	ops = l.balanceRegion.Schedule(c)
	if len(ops) > 0 {
	ops[0].SetDesc(fmt.Sprintf("scatter-range-region-%s", l.config.RangeName))
	ops[0].AttachKind(operator.OpRange)
	ops[0].Counters = append(ops[0].Counters,
	schedulerCounter.WithLabelValues(l.GetName(), "new-operator"),
	schedulerCounter.WithLabelValues(l.GetName(), "new-region-operator"),
	)
	return ops
	}
	schedulerCounter.WithLabelValues(l.GetName(), "no-need").Inc()
	return nil
	}

We use region limit here to decide if the scatter range scheduler can schedule but actually, we also use this scheduler to scatter leader which needs to be considered.

BTW, OpRange here is not very useful. IMO, we can remove it and directly use OpRegion.

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

master (ca53ac6)