check: remove orphan peer only when the peers is greater than the rul…

…e count (tikv#7581) (tikv#7591)

close tikv#7584

The healthy orphan peer should be the last one to be removed only if there are extra peers to keep the high availablility.

Signed-off-by: ti-chi-bot <ti-community-prow-bot@tidb.io>
Signed-off-by: bufferflies <1045931706@qq.com>

Co-authored-by: tongjian <1045931706@qq.com>
Co-authored-by: bufferflies <1045931706@qq.com>

server/schedule/checker/rule_checker.go

@@ -506,6 +506,7 @@ func (c *RuleChecker) fixOrphanPeers(region *core.RegionInfo, fit *placement.Reg
 		}
 	}
 
+	extra := fit.ExtraCount()
 	// If hasUnhealthyFit is true, try to remove unhealthy orphan peers only if number of OrphanPeers is >= 2.
 	// Ref https://github.com/tikv/pd/issues/4045
 	if len(fit.OrphanPeers) >= 2 {
@@ -522,7 +523,8 @@ func (c *RuleChecker) fixOrphanPeers(region *core.RegionInfo, fit *placement.Reg
 				checkerCounter.WithLabelValues("rule_checker", "remove-orphan-peer").Inc()
 				return operator.CreateRemovePeerOperator("remove-unhealthy-orphan-peer", c.cluster, 0, region, orphanPeer.StoreId)
 			}
-			if hasHealthPeer {
+			// The healthy orphan peer can be removed to keep the high availability only if the peer count is greater than the rule requirement.
+			if hasHealthPeer && extra > 0 {
 				// there already exists a healthy orphan peer, so we can remove other orphan Peers.
 				checkerCounter.WithLabelValues("rule_checker", "remove-orphan-peer").Inc()
 				// if there exists a disconnected orphan peer, we will pick it to remove firstly.

server/schedule/checker/rule_checker_test.go

@@ -1883,3 +1883,39 @@ func (suite *ruleCheckerTestSuite) TestTiFlashLocationLabels() {
 	op := suite.rc.Check(suite.cluster.GetRegion(1))
 	suite.Nil(op)
 }
+
+func (suite *ruleCheckerTestSuite) TestRemoveOrphanPeer() {
+	suite.cluster.AddLabelsStore(1, 1, map[string]string{"zone": "z1", "host": "h1"})
+	suite.cluster.AddLabelsStore(2, 1, map[string]string{"zone": "z1", "host": "h1"})
+	suite.cluster.AddLabelsStore(3, 1, map[string]string{"zone": "z1", "host": "h1"})
+	suite.cluster.AddLabelsStore(4, 1, map[string]string{"zone": "z2", "host": "h1"})
+	suite.cluster.AddLabelsStore(5, 1, map[string]string{"zone": "z2", "host": "h2"})
+	suite.cluster.AddLabelsStore(6, 1, map[string]string{"zone": "z2", "host": "h2"})
+	rule := &placement.Rule{
+		GroupID: "pd",
+		ID:      "test2",
+		Role:    placement.Voter,
+		Count:   3,
+		LabelConstraints: []placement.LabelConstraint{
+			{
+				Key:    "zone",
+				Op:     placement.In,
+				Values: []string{"z2"},
+			},
+		},
+	}
+	suite.ruleManager.SetRule(rule)
+	suite.ruleManager.DeleteRule("pd", "default")
+
+	// case1: regionA has 3 peers but not extra peer can be removed, so it needs to add peer first
+	suite.cluster.AddLeaderRegionWithRange(1, "200", "300", 1, 2, 3)
+	op := suite.rc.Check(suite.cluster.GetRegion(1))
+	suite.NotNil(op)
+	suite.Equal("add-rule-peer", op.Desc())
+
+	// case2: regionB has 4 peers and one extra peer can be removed, so it needs to remove extra peer first
+	suite.cluster.AddLeaderRegionWithRange(2, "300", "400", 1, 2, 3, 4)
+	op = suite.rc.Check(suite.cluster.GetRegion(2))
+	suite.NotNil(op)
+	suite.Equal("remove-orphan-peer", op.Desc())
+}

server/schedule/placement/fit.go

@@ -112,6 +112,15 @@ func (f *RegionFit) IsSatisfied() bool {
 	return len(f.OrphanPeers) == 0
 }
 
+// ExtraCount return the extra count.
+func (f *RegionFit) ExtraCount() int {
+	desired := 0
+	for _, r := range f.RuleFits {
+		desired += r.Rule.Count
+	}
+	return len(f.regionStores) - desired
+}
+
 // GetRuleFit returns the RuleFit that contains the peer.
 func (f *RegionFit) GetRuleFit(peerID uint64) *RuleFit {
 	for _, rf := range f.RuleFits {