Revert "placement: merge the rules if the constraints are the same (#… (#47527)

ref tikv/pd#7185

Author: nolouch

ddl/placement/BUILD.bazel

@@ -35,7 +35,7 @@ go_test(
     embed = [":placement"],
     flaky = True,
     race = "on",
-    shard_count = 25,
+    shard_count = 24,
     deps = [
         "//kv",
         "//meta",

ddl/placement/bundle.go

@@ -288,13 +288,27 @@ func (b *Bundle) String() string {
 
 // Tidy will post optimize Rules, trying to generate rules that suits PD.
 func (b *Bundle) Tidy() error {
-	tempRules := b.Rules[:0]
-	id := 0
+	extraCnt := map[PeerRoleType]int{}
+	newRules := b.Rules[:0]
+
+	// One Bundle is from one PlacementSettings, rule share same location labels, so we can use the first rule's location labels.
+	var locationLabels []string
 	for _, rule := range b.Rules {
+		if len(rule.LocationLabels) > 0 {
+			locationLabels = rule.LocationLabels
+			break
+		}
+	}
+	for i, rule := range b.Rules {
 		// useless Rule
 		if rule.Count <= 0 {
 			continue
 		}
+		// merge all empty constraints
+		if len(rule.Constraints) == 0 {
+			extraCnt[rule.Role] += rule.Count
+			continue
+		}
 		// refer to tidb#22065.
 		// add -engine=tiflash to every rule to avoid schedules to tiflash instances.
 		// placement rules in SQL is not compatible with `set tiflash replica` yet
@@ -306,139 +320,36 @@ func (b *Bundle) Tidy() error {
 		if err != nil {
 			return err
 		}
-		rule.ID = strconv.Itoa(id)
-		tempRules = append(tempRules, rule)
-		id++
-	}
-
-	groups := make(map[string]*constraintsGroup)
-	finalRules := tempRules[:0]
-	for _, rule := range tempRules {
-		key := rule.Constraints.FingerPrint()
-		existing, ok := groups[key]
-		if !ok {
-			groups[key] = &constraintsGroup{rules: []*Rule{rule}}
+		// Constraints.Add() will automatically avoid duplication
+		// if -engine=tiflash is added and there is only one constraint
+		// then it must be -engine=tiflash
+		// it is seen as an empty constraint, so merge it
+		if len(rule.Constraints) == 1 {
+			extraCnt[rule.Role] += rule.Count
 			continue
 		}
-		existing.rules = append(existing.rules, rule)
-	}
-	for _, group := range groups {
-		group.MergeRulesByRole()
-	}
-	if err := transformableLeaderConstraint(groups); err != nil {
-		return err
-	}
-	for _, group := range groups {
-		finalRules = append(finalRules, group.rules...)
-	}
-	// sort by id
-	sort.SliceStable(finalRules, func(i, j int) bool {
-		return finalRules[i].ID < finalRules[j].ID
-	})
-	b.Rules = finalRules
-	return nil
-}
-
-// constraintsGroup is a group of rules with the same constraints.
-type constraintsGroup struct {
-	rules []*Rule
-	// canBecameLeader means the group has leader/voter role,
-	// it's valid if it has leader.
-	canBecameLeader bool
-	// isLeaderGroup means it has specified leader role in this group.
-	isLeaderGroup bool
-}
-
-func transformableLeaderConstraint(groups map[string]*constraintsGroup) error {
-	var leaderGroup *constraintsGroup
-	canBecameLeaderNum := 0
-	for _, group := range groups {
-		if group.isLeaderGroup {
-			if leaderGroup != nil {
-				return ErrInvalidPlacementOptions
-			}
-			leaderGroup = group
-		}
-		if group.canBecameLeader {
-			canBecameLeaderNum++
-		}
-	}
-	// If there is a specified group should have leader, and only this group can be a leader, that means
-	// the leader's priority is certain, so we can merge the transformable rules into one.
-	// eg:
-	//  - [ group1 (L F), group2 (F) ], after merging is [group1 (2*V), group2 (F)], we still know the leader prefers group1.
-	//  - [ group1 (L F), group2 (V) ], after merging is [group1 (2*V), group2 (V)], we can't know leader priority after merge.
-	if leaderGroup != nil && canBecameLeaderNum == 1 {
-		leaderGroup.MergeTransformableRoles()
+		rule.ID = strconv.Itoa(i)
+		newRules = append(newRules, rule)
+	}
+	for role, cnt := range extraCnt {
+		// add -engine=tiflash, refer to tidb#22065.
+		newRules = append(newRules, &Rule{
+			ID:    string(role),
+			Role:  role,
+			Count: cnt,
+			Constraints: []Constraint{{
+				Op:     NotIn,
+				Key:    EngineLabelKey,
+				Values: []string{EngineLabelTiFlash},
+			}},
+			// the merged rule should have the same location labels with the original rules.
+			LocationLabels: locationLabels,
+		})
 	}
+	b.Rules = newRules
 	return nil
 }
 
-// MergeRulesByRole merges the rules with the same role.
-func (c *constraintsGroup) MergeRulesByRole() {
-	// Create a map to store rules by role
-	rulesByRole := make(map[PeerRoleType][]*Rule)
-
-	// Iterate through each rule
-	for _, rule := range c.rules {
-		// Add the rule to the map based on its role
-		rulesByRole[rule.Role] = append(rulesByRole[rule.Role], rule)
-		if rule.Role == Leader || rule.Role == Voter {
-			c.canBecameLeader = true
-		}
-		if rule.Role == Leader {
-			c.isLeaderGroup = true
-		}
-	}
-
-	// Clear existing rules
-	c.rules = nil
-
-	// Iterate through each role and merge the rules
-	for _, rules := range rulesByRole {
-		mergedRule := rules[0]
-		for i, rule := range rules {
-			if i == 0 {
-				continue
-			}
-			mergedRule.Count += rule.Count
-			if mergedRule.ID > rule.ID {
-				mergedRule.ID = rule.ID
-			}
-		}
-		c.rules = append(c.rules, mergedRule)
-	}
-}
-
-// MergeTransformableRoles merges all the rules to one that can be transformed to other roles.
-func (c *constraintsGroup) MergeTransformableRoles() {
-	if len(c.rules) == 0 || len(c.rules) == 1 {
-		return
-	}
-	var mergedRule *Rule
-	newRules := make([]*Rule, 0, len(c.rules))
-	for _, rule := range c.rules {
-		// Learner is not transformable, it should be promote by PD.
-		if rule.Role == Learner {
-			newRules = append(newRules, rule)
-			continue
-		}
-		if mergedRule == nil {
-			mergedRule = rule
-			continue
-		}
-		mergedRule.Count += rule.Count
-		if mergedRule.ID > rule.ID {
-			mergedRule.ID = rule.ID
-		}
-	}
-	if mergedRule != nil {
-		mergedRule.Role = Voter
-		newRules = append(newRules, mergedRule)
-	}
-	c.rules = newRules
-}
-
 // Reset resets the bundle ID and keyrange of all rules.
 func (b *Bundle) Reset(ruleIndex int, newIDs []int64) *Bundle {
 	// eliminate the redundant rules.