From 6804e876be33273dccd91fcdff1d85dd2c3943d5 Mon Sep 17 00:00:00 2001
From: Tobias Grieger <tobias.b.grieger@gmail.com>
Date: Wed, 5 Nov 2025 15:05:24 +0100
Subject: [PATCH 1/9] mmaprototype: avoid shadowing

loadSummary is also a type. Linter complained in CI all out of
a sudden :shrug:
---
 pkg/kv/kvserver/allocator/mmaprototype/load.go | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/pkg/kv/kvserver/allocator/mmaprototype/load.go b/pkg/kv/kvserver/allocator/mmaprototype/load.go
index c64881a5e354..f0ff2fa341c4 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/load.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/load.go
@@ -492,7 +492,7 @@ func loadSummaryForDimension(
 	meanLoad LoadValue,
 	meanUtil float64,
 ) (summary loadSummary) {
-	loadSummary := loadLow
+	summ := loadLow
 	if dim == WriteBandwidth && capacity == UnknownCapacity {
 		// Ignore smaller than 1MiB differences in write bandwidth. This 1MiB
 		// value is somewhat arbitrary, but is based on EBS gp3 having a default
@@ -546,13 +546,13 @@ func loadSummaryForDimension(
 		meanFractionNoChange = 0.05
 	)
 	if fractionAbove > meanFractionSlow {
-		loadSummary = overloadSlow
+		summ = overloadSlow
 	} else if fractionAbove < meanFractionLow {
-		loadSummary = loadLow
+		summ = loadLow
 	} else if fractionAbove >= meanFractionNoChange {
-		loadSummary = loadNoChange
+		summ = loadNoChange
 	} else {
-		loadSummary = loadNormal
+		summ = loadNormal
 	}
 	if capacity != UnknownCapacity && meanUtil*1.1 < fractionUsed {
 		// Further tune the summary based on utilization.
@@ -575,9 +575,9 @@ func loadSummaryForDimension(
 		if meanUtil*1.75 < fractionUsed {
 			return min(summaryUpperBound, overloadSlow)
 		}
-		return min(summaryUpperBound, max(loadSummary, loadNoChange))
+		return min(summaryUpperBound, max(summ, loadNoChange))
 	}
-	return min(summaryUpperBound, loadSummary)
+	return min(summaryUpperBound, summ)
 }
 
 func highDiskSpaceUtilization(load LoadValue, capacity LoadValue) bool {

From 386c03d22443662a97cad1c7bf64f99249b8f483 Mon Sep 17 00:00:00 2001
From: Tobias Grieger <tobias.b.grieger@gmail.com>
Date: Wed, 5 Nov 2025 11:02:11 +0100
Subject: [PATCH 2/9] mmaprototype: remove failureDetectionSummary

We'll replace it with a store-level construct in follow-up commits.
---
 .../allocator/mmaprototype/allocator.go       |  4 --
 .../allocator/mmaprototype/allocator_state.go | 18 +-------
 .../allocator/mmaprototype/cluster_state.go   | 45 -------------------
 .../mmaprototype/cluster_state_test.go        | 17 +------
 .../kvserver/allocator/mmaprototype/load.go   |  5 +--
 .../testdata/cluster_state/multiple_ranges    |  8 ++--
 .../testdata/cluster_state/rebalance_replica  |  8 ++--
 .../testdata/cluster_state/remove_replica     |  8 ++--
 .../testdata/cluster_state/removed_ranges     |  8 ++--
 .../testdata/cluster_state/transfer_lease     | 16 +++----
 10 files changed, 29 insertions(+), 108 deletions(-)

diff --git a/pkg/kv/kvserver/allocator/mmaprototype/allocator.go b/pkg/kv/kvserver/allocator/mmaprototype/allocator.go
index 76b1d4eea9bf..02c032b9d4b7 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/allocator.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/allocator.go
@@ -43,10 +43,6 @@ type Allocator interface {
 	// stores.
 	RemoveNodeAndStores(nodeID roachpb.NodeID) error
 
-	// UpdateFailureDetectionSummary tells the allocator about the current
-	// failure detection state for a node. A node starts in the fdOK state.
-	UpdateFailureDetectionSummary(nodeID roachpb.NodeID, fd failureDetectionSummary) error
-
 	// ProcessStoreLoadMsg provides frequent the state of every store and its
 	// associated node in the cluster.
 	ProcessStoreLoadMsg(ctx context.Context, msg *StoreLoadMsg)
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go b/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go
index 30705cb93dab..3ba26816c9da 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go
@@ -493,10 +493,6 @@ func (a *allocatorState) rebalanceStores(
 						continue
 					}
 					candSls := a.cs.computeLoadSummary(ctx, cand.storeID, &means.storeLoad, &means.nodeLoad)
-					if sls.fd != fdOK {
-						log.KvDistribution.VInfof(ctx, 2, "skipping store s%d: failure detection status not OK", cand.storeID)
-						continue
-					}
 					candsSet.candidates = append(candsSet.candidates, candidateInfo{
 						StoreID:              cand.storeID,
 						storeLoadSummary:     candSls,
@@ -608,7 +604,7 @@ func (a *allocatorState) rebalanceStores(
 		// If the node is cpu overloaded, or the store/node is not fdOK, exclude
 		// the other stores on this node from receiving replicas shed by this
 		// store.
-		excludeStoresOnNode := store.nls > overloadSlow || store.fd != fdOK
+		excludeStoresOnNode := store.nls > overloadSlow
 		storesToExclude = storesToExclude[:0]
 		if excludeStoresOnNode {
 			nodeID := ss.NodeID
@@ -819,15 +815,6 @@ func (a *allocatorState) RemoveNodeAndStores(nodeID roachpb.NodeID) error {
 	panic("unimplemented")
 }
 
-// UpdateFailureDetectionSummary implements the Allocator interface.
-func (a *allocatorState) UpdateFailureDetectionSummary(
-	nodeID roachpb.NodeID, fd failureDetectionSummary,
-) error {
-	a.mu.Lock()
-	defer a.mu.Unlock()
-	panic("unimplemented")
-}
-
 // ProcessStoreLeaseholderMsg implements the Allocator interface.
 func (a *allocatorState) ProcessStoreLoadMsg(ctx context.Context, msg *StoreLoadMsg) {
 	a.mu.Lock()
@@ -1381,9 +1368,6 @@ func (a *allocatorState) computeCandidatesForRange(
 		}
 		ss := a.cs.stores[storeID]
 		csls := a.cs.meansMemo.getStoreLoadSummary(ctx, means, storeID, ss.loadSeqNum)
-		if csls.fd != fdOK {
-			continue
-		}
 		cset.candidates = append(cset.candidates, candidateInfo{
 			StoreID:          storeID,
 			storeLoadSummary: csls,
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/cluster_state.go b/pkg/kv/kvserver/allocator/mmaprototype/cluster_state.go
index 20f1d7029456..d78e9a8b5566 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/cluster_state.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/cluster_state.go
@@ -829,47 +829,10 @@ func newStoreState() *storeState {
 	return ss
 }
 
-// failureDetectionSummary is provided by an external entity and never
-// computed inside the allocator.
-type failureDetectionSummary uint8
-
-// All state transitions are permitted by the allocator. For example, fdDead
-// => fdOk is allowed since the allocator can simply stop shedding replicas
-// and then start adding replicas (if underloaded).
-const (
-	fdOK failureDetectionSummary = iota
-	// Don't add replicas or leases.
-	fdSuspect
-	// Move leases away. Don't add replicas or leases.
-	fdDrain
-	// Node is dead, so move leases and replicas away from it.
-	fdDead
-)
-
-func (fds failureDetectionSummary) String() string {
-	return redact.StringWithoutMarkers(fds)
-}
-
-// SafeFormat implements the redact.SafeFormatter interface.
-func (fds failureDetectionSummary) SafeFormat(w redact.SafePrinter, _ rune) {
-	switch fds {
-	case fdOK:
-		w.Print("ok")
-	case fdSuspect:
-		w.Print("suspect")
-	case fdDrain:
-		w.Print("drain")
-	case fdDead:
-		w.Print("dead")
-	}
-}
-
 type nodeState struct {
 	stores []roachpb.StoreID
 	NodeLoad
 	adjustedCPU LoadValue
-
-	fdSummary failureDetectionSummary
 }
 
 func newNodeState(nodeID roachpb.NodeID) *nodeState {
@@ -1905,13 +1868,6 @@ func (cs *clusterState) setStoreMembership(storeID roachpb.StoreID, state storeM
 	}
 }
 
-func (cs *clusterState) updateFailureDetectionSummary(
-	nodeID roachpb.NodeID, fd failureDetectionSummary,
-) {
-	ns := cs.nodes[nodeID]
-	ns.fdSummary = fd
-}
-
 //======================================================================
 // clusterState accessors:
 //
@@ -2193,7 +2149,6 @@ func computeLoadSummary(
 		nls:                        nls,
 		dimSummary:                 dimSummary,
 		highDiskSpaceUtilization:   highDiskSpaceUtil,
-		fd:                         ns.fdSummary,
 		maxFractionPendingIncrease: ss.maxFractionPendingIncrease,
 		maxFractionPendingDecrease: ss.maxFractionPendingDecrease,
 		loadSeqNum:                 ss.loadSeqNum,
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go b/pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go
index 5163bb0f5e20..b048593c437d 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go
@@ -301,8 +301,8 @@ func TestClusterState(t *testing.T) {
 				var buf strings.Builder
 				for _, nodeID := range nodeList {
 					ns := cs.nodes[roachpb.NodeID(nodeID)]
-					fmt.Fprintf(&buf, "node-id=%s failure-summary=%s locality-tiers=%s\n",
-						ns.NodeID, ns.fdSummary, cs.stores[ns.stores[0]].StoreAttributesAndLocality.locality())
+					fmt.Fprintf(&buf, "node-id=%s locality-tiers=%s\n",
+						ns.NodeID, cs.stores[ns.stores[0]].StoreAttributesAndLocality.locality())
 					for _, storeID := range ns.stores {
 						ss := cs.stores[storeID]
 						fmt.Fprintf(&buf, "  store-id=%v membership=%v attrs=%s locality-code=%s\n",
@@ -386,19 +386,6 @@ func TestClusterState(t *testing.T) {
 					printPostingList(&buf, removedStores)
 					return buf.String()
 
-				case "update-failure-detection":
-					nodeID := dd.ScanArg[roachpb.NodeID](t, d, "node-id")
-					failureDetectionString := dd.ScanArg[string](t, d, "summary")
-					var fd failureDetectionSummary
-					for i := fdOK; i < fdDead+1; i++ {
-						if i.String() == failureDetectionString {
-							fd = i
-							break
-						}
-					}
-					cs.updateFailureDetectionSummary(nodeID, fd)
-					return printNodeListMeta()
-
 				case "store-load-msg":
 					msg := parseStoreLoadMsg(t, d.Input)
 					cs.processStoreLoadMsg(context.Background(), &msg)
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/load.go b/pkg/kv/kvserver/allocator/mmaprototype/load.go
index f0ff2fa341c4..3700a86724b4 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/load.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/load.go
@@ -197,7 +197,6 @@ type storeLoadSummary struct {
 	nls                                                    loadSummary
 	dimSummary                                             [NumLoadDimensions]loadSummary
 	highDiskSpaceUtilization                               bool
-	fd                                                     failureDetectionSummary
 	maxFractionPendingIncrease, maxFractionPendingDecrease float64
 
 	loadSeqNum uint64
@@ -208,9 +207,9 @@ func (sls storeLoadSummary) String() string {
 }
 
 func (sls storeLoadSummary) SafeFormat(w redact.SafePrinter, _ rune) {
-	w.Printf("(store=%v worst=%v cpu=%v writes=%v bytes=%v node=%v high_disk=%v fd=%v, frac_pending=%.2f,%.2f(%t))",
+	w.Printf("(store=%v worst=%v cpu=%v writes=%v bytes=%v node=%v high_disk=%v frac_pending=%.2f,%.2f(%t))",
 		sls.sls, sls.worstDim, sls.dimSummary[CPURate], sls.dimSummary[WriteBandwidth], sls.dimSummary[ByteSize],
-		sls.nls, sls.highDiskSpaceUtilization, sls.fd, sls.maxFractionPendingIncrease,
+		sls.nls, sls.highDiskSpaceUtilization, sls.maxFractionPendingIncrease,
 		sls.maxFractionPendingDecrease,
 		sls.maxFractionPendingIncrease < epsilon && sls.maxFractionPendingDecrease < epsilon)
 }
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/multiple_ranges b/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/multiple_ranges
index 216e0526daa1..346050c75317 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/multiple_ranges
+++ b/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/multiple_ranges
@@ -2,10 +2,10 @@ set-store
   store-id=1 node-id=1 attrs=purple locality-tiers=region=us-west-1,zone=us-west-1a
   store-id=2 node-id=2 attrs=yellow locality-tiers=region=us-east-1,zone=us-east-1a
 ----
-node-id=1 failure-summary=ok locality-tiers=region=us-west-1,zone=us-west-1a,node=1
-  store-id=1 membership=full attrs=purple locality-code=1:2:3:
-node-id=2 failure-summary=ok locality-tiers=region=us-east-1,zone=us-east-1a,node=2
-  store-id=2 membership=full attrs=yellow locality-code=4:5:6:
+node-id=1 locality-tiers=region=us-west-1,zone=us-west-1a,node=1
+  store-id=1 attrs=purple locality-code=1:2:3:
+node-id=2 locality-tiers=region=us-east-1,zone=us-east-1a,node=2
+  store-id=2 attrs=yellow locality-code=4:5:6:
 
 # Both stores are more constrained wrt CPURate.
 store-load-msg
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/rebalance_replica b/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/rebalance_replica
index b691506e6ed0..55203ea8a691 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/rebalance_replica
+++ b/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/rebalance_replica
@@ -2,10 +2,10 @@ set-store
   store-id=1 node-id=1 attrs=purple locality-tiers=region=us-west-1,zone=us-west-1a
   store-id=2 node-id=2 attrs=yellow locality-tiers=region=us-east-1,zone=us-east-1a
 ----
-node-id=1 failure-summary=ok locality-tiers=region=us-west-1,zone=us-west-1a,node=1
-  store-id=1 membership=full attrs=purple locality-code=1:2:3:
-node-id=2 failure-summary=ok locality-tiers=region=us-east-1,zone=us-east-1a,node=2
-  store-id=2 membership=full attrs=yellow locality-code=4:5:6:
+node-id=1 locality-tiers=region=us-west-1,zone=us-west-1a,node=1
+  store-id=1 attrs=purple locality-code=1:2:3:
+node-id=2 locality-tiers=region=us-east-1,zone=us-east-1a,node=2
+  store-id=2 attrs=yellow locality-code=4:5:6:
 
 store-load-msg
   store-id=1 node-id=1 load=[80,80,80] capacity=[100,100,100] secondary-load=0 load-time=0s
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/remove_replica b/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/remove_replica
index c677b308c7ad..40c26673df7c 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/remove_replica
+++ b/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/remove_replica
@@ -2,10 +2,10 @@ set-store
   store-id=1 node-id=1 attrs=purple locality-tiers=region=us-west-1,zone=us-west-1a
   store-id=2 node-id=2 attrs=yellow locality-tiers=region=us-east-1,zone=us-east-1a
 ----
-node-id=1 failure-summary=ok locality-tiers=region=us-west-1,zone=us-west-1a,node=1
-  store-id=1 membership=full attrs=purple locality-code=1:2:3:
-node-id=2 failure-summary=ok locality-tiers=region=us-east-1,zone=us-east-1a,node=2
-  store-id=2 membership=full attrs=yellow locality-code=4:5:6:
+node-id=1 locality-tiers=region=us-west-1,zone=us-west-1a,node=1
+  store-id=1 attrs=purple locality-code=1:2:3:
+node-id=2 locality-tiers=region=us-east-1,zone=us-east-1a,node=2
+  store-id=2 attrs=yellow locality-code=4:5:6:
 
 store-load-msg
   store-id=2 node-id=2 load=[20,80,80] capacity=[100,100,100] secondary-load=0 load-time=0s
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/removed_ranges b/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/removed_ranges
index 2cd0f0a57bcf..3658bdbb29df 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/removed_ranges
+++ b/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/removed_ranges
@@ -5,10 +5,10 @@ set-store
   store-id=1 node-id=1 attrs=purple locality-tiers=region=us-west-1,zone=us-west-1a
   store-id=2 node-id=2 attrs=yellow locality-tiers=region=us-east-1,zone=us-east-1a
 ----
-node-id=1 failure-summary=ok locality-tiers=region=us-west-1,zone=us-west-1a,node=1
-  store-id=1 membership=full attrs=purple locality-code=1:2:3:
-node-id=2 failure-summary=ok locality-tiers=region=us-east-1,zone=us-east-1a,node=2
-  store-id=2 membership=full attrs=yellow locality-code=4:5:6:
+node-id=1 locality-tiers=region=us-west-1,zone=us-west-1a,node=1
+  store-id=1 attrs=purple locality-code=1:2:3:
+node-id=2 locality-tiers=region=us-east-1,zone=us-east-1a,node=2
+  store-id=2 attrs=yellow locality-code=4:5:6:
 
 store-leaseholder-msg 
 store-id=1
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/transfer_lease b/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/transfer_lease
index bc2167e8363f..5cc84f5dd438 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/transfer_lease
+++ b/pkg/kv/kvserver/allocator/mmaprototype/testdata/cluster_state/transfer_lease
@@ -2,10 +2,10 @@ set-store
   store-id=1 node-id=1 attrs=purple locality-tiers=region=us-west-1,zone=us-west-1a
   store-id=2 node-id=2 attrs=yellow locality-tiers=region=us-east-1,zone=us-east-1a
 ----
-node-id=1 failure-summary=ok locality-tiers=region=us-west-1,zone=us-west-1a,node=1
-  store-id=1 membership=full attrs=purple locality-code=1:2:3:
-node-id=2 failure-summary=ok locality-tiers=region=us-east-1,zone=us-east-1a,node=2
-  store-id=2 membership=full attrs=yellow locality-code=4:5:6:
+node-id=1 locality-tiers=region=us-west-1,zone=us-west-1a,node=1
+  store-id=1 attrs=purple locality-code=1:2:3:
+node-id=2 locality-tiers=region=us-east-1,zone=us-east-1a,node=2
+  store-id=2 attrs=yellow locality-code=4:5:6:
 
 store-load-msg
   store-id=1 node-id=1 load=[80,80,80] capacity=[100,100,100] secondary-load=1 load-time=0s
@@ -86,7 +86,7 @@ set-store
   store-id=1 node-id=1 attrs=purple locality-tiers=region=us-west-1,zone=us-west-1a
   store-id=2 node-id=2 attrs=yellow locality-tiers=region=us-east-1,zone=us-east-1a
 ----
-node-id=1 failure-summary=ok locality-tiers=region=us-west-1,zone=us-west-1a,node=1
-  store-id=1 membership=full attrs=purple locality-code=1:2:3:
-node-id=2 failure-summary=ok locality-tiers=region=us-east-1,zone=us-east-1a,node=2
-  store-id=2 membership=full attrs=yellow locality-code=4:5:6:
+node-id=1 locality-tiers=region=us-west-1,zone=us-west-1a,node=1
+  store-id=1 attrs=purple locality-code=1:2:3:
+node-id=2 locality-tiers=region=us-east-1,zone=us-east-1a,node=2
+  store-id=2 attrs=yellow locality-code=4:5:6:

From d6a097c29c51f122e53b614a4a9684c5309afd5c Mon Sep 17 00:00:00 2001
From: Tobias Grieger <tobias.b.grieger@gmail.com>
Date: Wed, 5 Nov 2025 11:06:17 +0100
Subject: [PATCH 3/9] mmaprototype: remove storeMembership

We'll replace it with a store-level construct in follow-up commits.
---
 .../allocator/mmaprototype/cluster_state.go   | 36 -----------------
 .../mmaprototype/cluster_state_test.go        | 39 +++----------------
 2 files changed, 5 insertions(+), 70 deletions(-)

diff --git a/pkg/kv/kvserver/allocator/mmaprototype/cluster_state.go b/pkg/kv/kvserver/allocator/mmaprototype/cluster_state.go
index d78e9a8b5566..78bbd0ed74ef 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/cluster_state.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/cluster_state.go
@@ -597,37 +597,9 @@ type pendingReplicaChange struct {
 	enactedAtTime time.Time
 }
 
-// TODO(kvoli): This will eventually be used to represent the state of a node's
-// membership. This corresponds to non-decommissioning, decommissioning and
-// decommissioned. Fill in commentary and use.
-type storeMembership int8
-
-const (
-	storeMembershipMember storeMembership = iota
-	storeMembershipRemoving
-	storeMembershipRemoved
-)
-
-func (s storeMembership) String() string {
-	return redact.StringWithoutMarkers(s)
-}
-
-// SafeFormat implements the redact.SafeFormatter interface.
-func (s storeMembership) SafeFormat(w redact.SafePrinter, _ rune) {
-	switch s {
-	case storeMembershipMember:
-		w.Print("full")
-	case storeMembershipRemoving:
-		w.Print("removing")
-	case storeMembershipRemoved:
-		w.Print("removed")
-	}
-}
-
 // storeState maintains the complete state about a store as known to the
 // allocator.
 type storeState struct {
-	storeMembership
 	storeLoad
 	StoreAttributesAndLocality
 	adjusted struct {
@@ -1860,14 +1832,6 @@ func (cs *clusterState) setStore(sal StoreAttributesAndLocality) {
 	}
 }
 
-func (cs *clusterState) setStoreMembership(storeID roachpb.StoreID, state storeMembership) {
-	if ss, ok := cs.stores[storeID]; ok {
-		ss.storeMembership = state
-	} else {
-		panic(fmt.Sprintf("store %d not found in cluster state", storeID))
-	}
-}
-
 //======================================================================
 // clusterState accessors:
 //
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go b/pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go
index b048593c437d..27a398b5bdbf 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go
@@ -207,7 +207,7 @@ func printPendingChangesTest(changes []*pendingReplicaChange) string {
 	return buf.String()
 }
 
-func testingGetStoreList(t *testing.T, cs *clusterState) (member, removed storeIDPostingList) {
+func testingGetStoreList(t *testing.T, cs *clusterState) storeIDPostingList {
 	var clusterStoreList, nodeStoreList storeIDPostingList
 	// Ensure that the storeIDs in the cluster store map and the stores listed
 	// under each node are the same.
@@ -222,15 +222,7 @@ func testingGetStoreList(t *testing.T, cs *clusterState) (member, removed storeI
 	require.True(t, clusterStoreList.isEqual(nodeStoreList),
 		"expected store lists to be equal %v != %v", clusterStoreList, nodeStoreList)
 
-	for storeID, ss := range cs.stores {
-		switch ss.storeMembership {
-		case storeMembershipMember, storeMembershipRemoving:
-			member.insert(storeID)
-		case storeMembershipRemoved:
-			removed.insert(storeID)
-		}
-	}
-	return member, removed
+	return clusterStoreList
 }
 
 func testingGetPendingChanges(t *testing.T, cs *clusterState) []*pendingReplicaChange {
@@ -305,8 +297,8 @@ func TestClusterState(t *testing.T) {
 						ns.NodeID, cs.stores[ns.stores[0]].StoreAttributesAndLocality.locality())
 					for _, storeID := range ns.stores {
 						ss := cs.stores[storeID]
-						fmt.Fprintf(&buf, "  store-id=%v membership=%v attrs=%s locality-code=%s\n",
-							ss.StoreID, ss.storeMembership, ss.StoreAttrs, ss.localityTiers.str)
+						fmt.Fprintf(&buf, "  store-id=%v attrs=%s locality-code=%s\n",
+							ss.StoreID, ss.StoreAttrs, ss.localityTiers.str)
 					}
 				}
 				return buf.String()
@@ -336,7 +328,7 @@ func TestClusterState(t *testing.T) {
 
 				case "get-load-info":
 					var buf strings.Builder
-					memberStores, _ := testingGetStoreList(t, cs)
+					memberStores := testingGetStoreList(t, cs)
 					for _, storeID := range memberStores {
 						ss := cs.stores[storeID]
 						ns := cs.nodes[ss.NodeID]
@@ -365,27 +357,6 @@ func TestClusterState(t *testing.T) {
 					}
 					return printNodeListMeta()
 
-				case "set-store-membership":
-					storeID := dd.ScanArg[roachpb.StoreID](t, d, "store-id")
-					var storeMembershipVal storeMembership
-					switch str := dd.ScanArg[string](t, d, "membership"); str {
-					case "member":
-						storeMembershipVal = storeMembershipMember
-					case "removing":
-						storeMembershipVal = storeMembershipRemoving
-					case "removed":
-						storeMembershipVal = storeMembershipRemoved
-					}
-					cs.setStoreMembership(storeID, storeMembershipVal)
-
-					var buf strings.Builder
-					nonRemovedStores, removedStores := testingGetStoreList(t, cs)
-					buf.WriteString("member store-ids: ")
-					printPostingList(&buf, nonRemovedStores)
-					buf.WriteString("\nremoved store-ids: ")
-					printPostingList(&buf, removedStores)
-					return buf.String()
-
 				case "store-load-msg":
 					msg := parseStoreLoadMsg(t, d.Input)
 					cs.processStoreLoadMsg(context.Background(), &msg)

From 5e1f3f157d9b792ccbe5df14250ac794f17e9012 Mon Sep 17 00:00:00 2001
From: Tobias Grieger <tobias.b.grieger@gmail.com>
Date: Wed, 5 Nov 2025 11:26:25 +0100
Subject: [PATCH 4/9] mmaprototype: move and rename storeIDPostingList ->
 storeSet

---
 .../allocator/mmaprototype/BUILD.bazel        |   1 +
 .../allocator/mmaprototype/allocator_state.go |   8 +-
 .../mmaprototype/cluster_state_test.go        |   4 +-
 .../allocator/mmaprototype/constraint.go      | 156 +----------------
 .../mmaprototype/constraint_matcher.go        |  32 ++--
 .../mmaprototype/constraint_matcher_test.go   |   8 +-
 .../allocator/mmaprototype/constraint_test.go |   6 +-
 .../kvserver/allocator/mmaprototype/load.go   |   2 +-
 .../allocator/mmaprototype/memo_helper.go     |   2 +-
 .../allocator/mmaprototype/store_set.go       | 157 ++++++++++++++++++
 10 files changed, 193 insertions(+), 183 deletions(-)
 create mode 100644 pkg/kv/kvserver/allocator/mmaprototype/store_set.go

diff --git a/pkg/kv/kvserver/allocator/mmaprototype/BUILD.bazel b/pkg/kv/kvserver/allocator/mmaprototype/BUILD.bazel
index 9832aaf9ca8b..31d3d1d5c8b8 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/BUILD.bazel
+++ b/pkg/kv/kvserver/allocator/mmaprototype/BUILD.bazel
@@ -13,6 +13,7 @@ go_library(
         "memo_helper.go",
         "messages.go",
         "rebalance_advisor.go",
+        "store_set.go",
         "top_k_replicas.go",
     ],
     importpath = "github.com/cockroachdb/cockroach/pkg/kv/kvserver/allocator/mmaprototype",
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go b/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go
index 3ba26816c9da..57b3766719a5 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go
@@ -353,8 +353,8 @@ func (a *allocatorState) rebalanceStores(
 
 	var changes []PendingRangeChange
 	var disj [1]constraintsConj
-	var storesToExclude storeIDPostingList
-	var storesToExcludeForRange storeIDPostingList
+	var storesToExclude storeSet
+	var storesToExcludeForRange storeSet
 	scratchNodes := map[roachpb.NodeID]*NodeLoad{}
 	scratchStores := map[roachpb.StoreID]struct{}{}
 	// The caller has a fixed concurrency limit it can move ranges at, when it
@@ -461,7 +461,7 @@ func (a *allocatorState) rebalanceStores(
 						store.StoreID, rangeID))
 				}
 				cands, _ := rstate.constraints.candidatesToMoveLease()
-				var candsPL storeIDPostingList
+				var candsPL storeSet
 				for _, cand := range cands {
 					candsPL.insert(cand.storeID)
 				}
@@ -1347,7 +1347,7 @@ func (a *allocatorState) ensureAnalyzedConstraints(rstate *rangeState) bool {
 func (a *allocatorState) computeCandidatesForRange(
 	ctx context.Context,
 	expr constraintsDisj,
-	storesToExclude storeIDPostingList,
+	storesToExclude storeSet,
 	loadSheddingStore roachpb.StoreID,
 ) (_ candidateSet, sheddingSLS storeLoadSummary) {
 	means := a.cs.meansMemo.getMeans(expr)
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go b/pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go
index 27a398b5bdbf..fb4b622444b0 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/cluster_state_test.go
@@ -207,8 +207,8 @@ func printPendingChangesTest(changes []*pendingReplicaChange) string {
 	return buf.String()
 }
 
-func testingGetStoreList(t *testing.T, cs *clusterState) storeIDPostingList {
-	var clusterStoreList, nodeStoreList storeIDPostingList
+func testingGetStoreList(t *testing.T, cs *clusterState) storeSet {
+	var clusterStoreList, nodeStoreList storeSet
 	// Ensure that the storeIDs in the cluster store map and the stores listed
 	// under each node are the same.
 	for storeID := range cs.stores {
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/constraint.go b/pkg/kv/kvserver/allocator/mmaprototype/constraint.go
index c9acc0d49f56..5ffc9e628af4 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/constraint.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/constraint.go
@@ -24,7 +24,7 @@ import (
 // and constraints conjunctions. The primary ones are normalizedSpanConfig and
 // rangeAnalyzedConstraints.
 //
-// Other misc pieces: storeIDPostingList represents a set of stores, and is
+// Other misc pieces: storeSet represents a set of stores, and is
 // used here and will be used elsewhere for set operations.
 // localityTierInterner is used for interning the tiers to avoid string
 // comparisons, used for diversity computation. It will also be used
@@ -1408,8 +1408,8 @@ func (rac *rangeAnalyzedConstraints) candidatesToConvertFromVoterToNonVoter() (
 	if constraintSetNeeded && !voterConstraintSetNeeded {
 		return constraintSet, nil
 	}
-	cset := makeStoreIDPostingList(constraintSet)
-	cset.intersect(makeStoreIDPostingList(voterConstraintSet))
+	cset := makeStoreSet(constraintSet)
+	cset.intersect(makeStoreSet(voterConstraintSet))
 	return cset, nil
 }
 
@@ -1945,152 +1945,6 @@ func (l localityTiers) diversityScore(other localityTiers) float64 {
 	return 0
 }
 
-// Ordered and de-duped list of storeIDs. Represents a set of stores. Used for
-// fast set operations for constraint satisfaction.
-type storeIDPostingList []roachpb.StoreID
-
-func makeStoreIDPostingList(a []roachpb.StoreID) storeIDPostingList {
-	slices.Sort(a)
-	return a
-}
-
-func (s *storeIDPostingList) union(b storeIDPostingList) {
-	a := *s
-	n := len(a)
-	m := len(b)
-	for i, j := 0, 0; j < m; {
-		if i < n && a[i] < b[j] {
-			i++
-			continue
-		}
-		// i >= n || a[i] >= b[j]
-		if i >= n || a[i] > b[j] {
-			a = append(a, b[j])
-			j++
-			continue
-		}
-		// a[i] == b[j]
-		i++
-		j++
-	}
-	if len(a) > n {
-		slices.Sort(a)
-		*s = a
-	}
-}
-
-func (s *storeIDPostingList) intersect(b storeIDPostingList) {
-	// TODO(sumeer): For larger lists, probe using smaller list.
-	a := *s
-	n := len(a)
-	m := len(b)
-	k := 0
-	for i, j := 0, 0; i < n && j < m; {
-		if a[i] < b[j] {
-			i++
-		} else if a[i] > b[j] {
-			j++
-		} else {
-			a[k] = a[i]
-			i++
-			j++
-			k++
-		}
-	}
-	*s = a[:k]
-}
-
-func (s *storeIDPostingList) isEqual(b storeIDPostingList) bool {
-	a := *s
-	n := len(a)
-	m := len(b)
-	if n != m {
-		return false
-	}
-	for i := range b {
-		if a[i] != b[i] {
-			return false
-		}
-	}
-	return true
-}
-
-// Returns true iff found (and successfully removed).
-func (s *storeIDPostingList) remove(storeID roachpb.StoreID) bool {
-	a := *s
-	n := len(a)
-	found := false
-	for i := range a {
-		if a[i] == storeID {
-			// INVARIANT: i < n, so i <= n-1 and i+1 <= n.
-			copy(a[i:n-1], a[i+1:n])
-			found = true
-			break
-		}
-	}
-	if !found {
-		return false
-	}
-	*s = a[:n-1]
-	return true
-}
-
-// Returns true iff the storeID was not already in the set.
-func (s *storeIDPostingList) insert(storeID roachpb.StoreID) bool {
-	a := *s
-	n := len(a)
-	var pos int
-	for pos = 0; pos < n; pos++ {
-		if storeID < a[pos] {
-			break
-		} else if storeID == a[pos] {
-			return false
-		}
-	}
-	var b storeIDPostingList
-	if cap(a) > n {
-		b = a[:n+1]
-	} else {
-		m := 2 * cap(a)
-		const minLength = 10
-		if m < minLength {
-			m = minLength
-		}
-		b = make([]roachpb.StoreID, n+1, m)
-		// Insert at pos, so pos-1 is the last element before the insertion.
-		if pos > 0 {
-			copy(b[:pos], a[:pos])
-		}
-	}
-	copy(b[pos+1:n+1], a[pos:n])
-	b[pos] = storeID
-	*s = b
-	return true
-}
-
-func (s *storeIDPostingList) contains(storeID roachpb.StoreID) bool {
-	_, found := slices.BinarySearch(*s, storeID)
-	return found
-}
-
-const (
-	// offset64 is the initial hash value, and is taken from fnv.go
-	offset64 = 14695981039346656037
-
-	// prime64 is a large-ish prime number used in hashing and taken from fnv.go.
-	prime64 = 1099511628211
-)
-
-// FNV-1a hash algorithm.
-func (s *storeIDPostingList) hash() uint64 {
-	h := uint64(offset64)
-	for _, storeID := range *s {
-		h ^= uint64(storeID)
-		h *= prime64
-	}
-	return h
-}
-
 const notMatchedLeasePreferencIndex = math.MaxInt32
 
 // matchedLeasePreferenceIndex returns the index of the lease preference that
@@ -2124,7 +1978,7 @@ var _ = analyzeConstraintsBuf{}
 var _ = storeAndLocality{}
 var _ = localityTierInterner{}
 var _ = localityTiers{}
-var _ = storeIDPostingList{}
+var _ = storeSet{}
 
 var _ = constraintsDisj{}.hash
 var _ = constraintsDisj{}.isEqual
@@ -2160,7 +2014,7 @@ func init() {
 	var lt localityTiers
 	var _ = lt.diversityScore
 
-	var pl storeIDPostingList
+	var pl storeSet
 	var _ = pl.union
 	var _ = pl.intersect
 	var _ = pl.isEqual
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/constraint_matcher.go b/pkg/kv/kvserver/allocator/mmaprototype/constraint_matcher.go
index 83b512cb39b9..4c157193e6d1 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/constraint_matcher.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/constraint_matcher.go
@@ -43,7 +43,7 @@ type matchedConstraints struct {
 }
 
 type matchedSet struct {
-	storeIDPostingList
+	storeSet
 }
 
 func newConstraintMatcher(interner *stringInterner) *constraintMatcher {
@@ -166,21 +166,21 @@ func (cm *constraintMatcher) getMatchedSetForConstraint(c internedConstraint) *m
 // constrainStoresForConjunction populates storeSet with the stores matching
 // the given conjunction of constraints.
 //
-// TODO(sumeer): make storeIDPostingList a struct and use a sync.Pool.
+// TODO(sumeer): make storeSet a struct and use a sync.Pool.
 func (cm *constraintMatcher) constrainStoresForConjunction(
-	constraints []internedConstraint, storeSet *storeIDPostingList,
+	constraints []internedConstraint, storeSet *storeSet,
 ) {
 	*storeSet = (*storeSet)[:0]
 	if len(constraints) == 0 {
-		*storeSet = append(*storeSet, cm.allStores.storeIDPostingList...)
+		*storeSet = append(*storeSet, cm.allStores.storeSet...)
 		return
 	}
 	for i := range constraints {
 		matchedSet := cm.getMatchedSetForConstraint(constraints[i])
 		if i == 0 {
-			*storeSet = append(*storeSet, matchedSet.storeIDPostingList...)
+			*storeSet = append(*storeSet, matchedSet.storeSet...)
 		} else {
-			storeSet.intersect(matchedSet.storeIDPostingList)
+			storeSet.intersect(matchedSet.storeSet)
 		}
 		if len(*storeSet) == 0 {
 			return
@@ -212,26 +212,24 @@ func (cm *constraintMatcher) storeMatches(
 
 // constrainStoresForExpr populates storeSet with the stores matching the
 // given expression.
-func (cm *constraintMatcher) constrainStoresForExpr(
-	expr constraintsDisj, storeSet *storeIDPostingList,
-) {
+func (cm *constraintMatcher) constrainStoresForExpr(expr constraintsDisj, set *storeSet) {
 	if len(expr) == 0 {
-		*storeSet = append(*storeSet, cm.allStores.storeIDPostingList...)
+		*set = append(*set, cm.allStores.storeSet...)
 		return
 	}
-	// Optimize for a single conjunction, by using storeSet directly in the call
+	// Optimize for a single conjunction, by using set directly in the call
 	// to constrainStoresForConjunction.
-	var scratch storeIDPostingList
-	scratchPtr := storeSet
+	var scratch storeSet
+	scratchPtr := set
 	for i := range expr {
 		cm.constrainStoresForConjunction(expr[i], scratchPtr)
 		if len(*scratchPtr) == 0 {
 			continue
 		}
-		if scratchPtr != storeSet {
-			storeSet.union(*scratchPtr)
+		if scratchPtr != set {
+			set.union(*scratchPtr)
 		} else {
-			// The storeSet contains the first non-empty set. Collect the remaining
+			// The set contains the first non-empty set. Collect the remaining
 			// sets in scratch.
 			scratchPtr = &scratch
 		}
@@ -251,7 +249,7 @@ func (cm *constraintMatcher) checkConsistency() error {
 		}
 	}
 	for c, pl := range cm.constraints {
-		for _, storeID := range pl.storeIDPostingList {
+		for _, storeID := range pl.storeSet {
 			store, ok := cm.stores[storeID]
 			if !ok {
 				return errors.AssertionFailedf("constraint set mentions unknown storeID %d", storeID)
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/constraint_matcher_test.go b/pkg/kv/kvserver/allocator/mmaprototype/constraint_matcher_test.go
index 3798c53a6723..79352082b6b8 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/constraint_matcher_test.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/constraint_matcher_test.go
@@ -77,15 +77,15 @@ func TestConstraintMatcher(t *testing.T) {
 						Value: interner.toString(c.value),
 					}
 					sepStr := ""
-					if len(pl.storeIDPostingList) > 0 {
+					if len(pl.storeSet) > 0 {
 						sepStr = " "
 					}
 					fmt.Fprintf(b, "%s:%s", rc.String(), sepStr)
-					printPostingList(b, pl.storeIDPostingList)
+					printPostingList(b, pl.storeSet)
 					fmt.Fprintf(b, "\n")
 				}
 				fmt.Fprintf(b, "all-stores: ")
-				printPostingList(b, cm.allStores.storeIDPostingList)
+				printPostingList(b, cm.allStores.storeSet)
 				fmt.Fprintf(b, "\n")
 				err := cm.checkConsistency()
 				require.NoError(t, err)
@@ -129,7 +129,7 @@ func TestConstraintMatcher(t *testing.T) {
 						disj = append(disj, interner.internConstraintsConj(cc))
 					}
 				}
-				var pl storeIDPostingList
+				var pl storeSet
 				if len(disj) <= 1 {
 					if randutil.FastUint32()%2 == 0 {
 						var conj []internedConstraint
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/constraint_test.go b/pkg/kv/kvserver/allocator/mmaprototype/constraint_test.go
index 6ed5083af78b..a418dc00242a 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/constraint_test.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/constraint_test.go
@@ -150,7 +150,7 @@ func TestNormalizedSpanConfig(t *testing.T) {
 		})
 }
 
-func printPostingList(b *strings.Builder, pl storeIDPostingList) {
+func printPostingList(b *strings.Builder, pl storeSet) {
 	for i := range pl {
 		prefix := ""
 		if i > 0 {
@@ -161,7 +161,7 @@ func printPostingList(b *strings.Builder, pl storeIDPostingList) {
 }
 
 func TestStoreIDPostingList(t *testing.T) {
-	pls := map[string]storeIDPostingList{}
+	pls := map[string]storeSet{}
 	forceAllocation := rand.Intn(2) == 1
 
 	datadriven.RunTest(t, "testdata/posting_list",
@@ -178,7 +178,7 @@ func TestStoreIDPostingList(t *testing.T) {
 						storeIDs = append(storeIDs, roachpb.StoreID(storeID))
 					}
 				}
-				pl := makeStoreIDPostingList(storeIDs)
+				pl := makeStoreSet(storeIDs)
 				if forceAllocation {
 					pl = pl[:len(pl):len(pl)]
 				}
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/load.go b/pkg/kv/kvserver/allocator/mmaprototype/load.go
index 3700a86724b4..58f2ba9cbfaa 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/load.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/load.go
@@ -228,7 +228,7 @@ func (sls storeLoadSummary) SafeFormat(w redact.SafePrinter, _ rune) {
 type meansForStoreSet struct {
 	constraintsDisj
 	meansLoad
-	stores         storeIDPostingList
+	stores         storeSet
 	storeSummaries map[roachpb.StoreID]storeLoadSummary
 }
 
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/memo_helper.go b/pkg/kv/kvserver/allocator/mmaprototype/memo_helper.go
index 2e2df169f76a..0dc15283bc8e 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/memo_helper.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/memo_helper.go
@@ -7,7 +7,7 @@ package mmaprototype
 
 // clearableMemoMap is a generic map suited to the needs of various memos used
 // in the allocator. The key is any type that implements the mapKey interface
-// (e.g. storeIDPostingList). There is no removal from the map since the memo
+// (e.g. storeSet). There is no removal from the map since the memo
 // is built up during an allocator round and then cleared for the next round.
 // The key-value pairs are stored in a mapEntry, which the caller is
 // responsible for initializing. The mapEntrySlice and its mapEntries are
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/store_set.go b/pkg/kv/kvserver/allocator/mmaprototype/store_set.go
new file mode 100644
index 000000000000..44f4631de1f0
--- /dev/null
+++ b/pkg/kv/kvserver/allocator/mmaprototype/store_set.go
@@ -0,0 +1,157 @@
+// Copyright 2025 The Cockroach Authors.
+//
+// Use of this software is governed by the CockroachDB Software License
+// included in the /LICENSE file.
+
+package mmaprototype
+
+import (
+	"slices"
+
+	"github.com/cockroachdb/cockroach/pkg/roachpb"
+)
+
+// Ordered and de-duped list of storeIDs. Represents a set of stores. Used for
+// fast set operations for constraint satisfaction.
+type storeSet []roachpb.StoreID
+
+func makeStoreSet(a []roachpb.StoreID) storeSet {
+	slices.Sort(a)
+	return a
+}
+
+func (s *storeSet) union(b storeSet) {
+	a := *s
+	n := len(a)
+	m := len(b)
+	for i, j := 0, 0; j < m; {
+		if i < n && a[i] < b[j] {
+			i++
+			continue
+		}
+		// i >= n || a[i] >= b[j]
+		if i >= n || a[i] > b[j] {
+			a = append(a, b[j])
+			j++
+			continue
+		}
+		// a[i] == b[j]
+		i++
+		j++
+	}
+	if len(a) > n {
+		slices.Sort(a)
+		*s = a
+	}
+}
+
+func (s *storeSet) intersect(b storeSet) {
+	// TODO(sumeer): For larger lists, probe using smaller list.
+	a := *s
+	n := len(a)
+	m := len(b)
+	k := 0
+	for i, j := 0, 0; i < n && j < m; {
+		if a[i] < b[j] {
+			i++
+		} else if a[i] > b[j] {
+			j++
+		} else {
+			a[k] = a[i]
+			i++
+			j++
+			k++
+		}
+	}
+	*s = a[:k]
+}
+
+func (s *storeSet) isEqual(b storeSet) bool {
+	a := *s
+	n := len(a)
+	m := len(b)
+	if n != m {
+		return false
+	}
+	for i := range b {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
+// Returns true iff found (and successfully removed).
+func (s *storeSet) remove(storeID roachpb.StoreID) bool {
+	a := *s
+	n := len(a)
+	found := false
+	for i := range a {
+		if a[i] == storeID {
+			// INVARIANT: i < n, so i <= n-1 and i+1 <= n.
+			copy(a[i:n-1], a[i+1:n])
+			found = true
+			break
+		}
+	}
+	if !found {
+		return false
+	}
+	*s = a[:n-1]
+	return true
+}
+
+// Returns true iff the storeID was not already in the set.
+func (s *storeSet) insert(storeID roachpb.StoreID) bool {
+	a := *s
+	n := len(a)
+	var pos int
+	for pos = 0; pos < n; pos++ {
+		if storeID < a[pos] {
+			break
+		} else if storeID == a[pos] {
+			return false
+		}
+	}
+	var b storeSet
+	if cap(a) > n {
+		b = a[:n+1]
+	} else {
+		m := 2 * cap(a)
+		const minLength = 10
+		if m < minLength {
+			m = minLength
+		}
+		b = make([]roachpb.StoreID, n+1, m)
+		// Insert at pos, so pos-1 is the last element before the insertion.
+		if pos > 0 {
+			copy(b[:pos], a[:pos])
+		}
+	}
+	copy(b[pos+1:n+1], a[pos:n])
+	b[pos] = storeID
+	*s = b
+	return true
+}
+
+func (s *storeSet) contains(storeID roachpb.StoreID) bool {
+	_, found := slices.BinarySearch(*s, storeID)
+	return found
+}
+
+const ( // offset64 is the initial hash value, and is taken from fnv.go
+	offset64 = 14695981039346656037
+
+	// prime64 is a large-ish prime number used in hashing and taken from fnv.go.
+	prime64 = 1099511628211
+)
+
+// FNV-1a hash algorithm.
+func (s *storeSet) hash() uint64 {
+	h := uint64(offset64)
+	for _, storeID := range *s {
+		h ^= uint64(storeID)
+		h *= prime64
+	}
+	return h
+}

From b9994d024987723d714edc38cb971fda45078893 Mon Sep 17 00:00:00 2001
From: Tobias Grieger <tobias.b.grieger@gmail.com>
Date: Wed, 5 Nov 2025 11:27:52 +0100
Subject: [PATCH 5/9] mmaprototype: fix a typo

---
 pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go | 2 +-
 pkg/kv/kvserver/allocator/mmaprototype/constraint.go      | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go b/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go
index 57b3766719a5..6f3e4301fc78 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go
@@ -1209,7 +1209,7 @@ func sortTargetCandidateSetAndPick(
 	// ones that have notMatchedLeasePreferenceIndex.
 	j = 0
 	for _, cand := range cands.candidates {
-		if cand.leasePreferenceIndex == notMatchedLeasePreferencIndex {
+		if cand.leasePreferenceIndex == notMatchedLeasePreferenceIndex {
 			break
 		}
 		j++
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/constraint.go b/pkg/kv/kvserver/allocator/mmaprototype/constraint.go
index 5ffc9e628af4..9eda7d628db7 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/constraint.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/constraint.go
@@ -1945,10 +1945,10 @@ func (l localityTiers) diversityScore(other localityTiers) float64 {
 	return 0
 }
 
-const notMatchedLeasePreferencIndex = math.MaxInt32
+const notMatchedLeasePreferenceIndex = math.MaxInt32
 
 // matchedLeasePreferenceIndex returns the index of the lease preference that
-// matches, else notMatchedLeasePreferencIndex
+// matches, else notMatchedLeasePreferenceIndex
 func matchedLeasePreferenceIndex(
 	storeID roachpb.StoreID,
 	leasePreferences []internedLeasePreference,
@@ -1962,7 +1962,7 @@ func matchedLeasePreferenceIndex(
 			return int32(j)
 		}
 	}
-	return notMatchedLeasePreferencIndex
+	return notMatchedLeasePreferenceIndex
 }
 
 // Avoid unused lint errors.

From 69cd6e4d6a5c0dc0993c118dc1e675f7dd0f4f9a Mon Sep 17 00:00:00 2001
From: Tobias Grieger <tobias.b.grieger@gmail.com>
Date: Wed, 5 Nov 2025 11:29:24 +0100
Subject: [PATCH 6/9] mmaprototype: move storeLoadSummary to its own file

---
 .../allocator/mmaprototype/BUILD.bazel        |  1 +
 .../kvserver/allocator/mmaprototype/load.go   | 23 --------------
 .../mmaprototype/store_load_summary.go        | 31 +++++++++++++++++++
 3 files changed, 32 insertions(+), 23 deletions(-)
 create mode 100644 pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go

diff --git a/pkg/kv/kvserver/allocator/mmaprototype/BUILD.bazel b/pkg/kv/kvserver/allocator/mmaprototype/BUILD.bazel
index 31d3d1d5c8b8..46a7dacf123b 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/BUILD.bazel
+++ b/pkg/kv/kvserver/allocator/mmaprototype/BUILD.bazel
@@ -13,6 +13,7 @@ go_library(
         "memo_helper.go",
         "messages.go",
         "rebalance_advisor.go",
+        "store_load_summary.go",
         "store_set.go",
         "top_k_replicas.go",
     ],
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/load.go b/pkg/kv/kvserver/allocator/mmaprototype/load.go
index 58f2ba9cbfaa..35b8e1b4a564 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/load.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/load.go
@@ -191,29 +191,6 @@ type meanNodeLoad struct {
 	utilCPU     float64
 }
 
-type storeLoadSummary struct {
-	worstDim                                               LoadDimension // for logging only
-	sls                                                    loadSummary
-	nls                                                    loadSummary
-	dimSummary                                             [NumLoadDimensions]loadSummary
-	highDiskSpaceUtilization                               bool
-	maxFractionPendingIncrease, maxFractionPendingDecrease float64
-
-	loadSeqNum uint64
-}
-
-func (sls storeLoadSummary) String() string {
-	return redact.StringWithoutMarkers(sls)
-}
-
-func (sls storeLoadSummary) SafeFormat(w redact.SafePrinter, _ rune) {
-	w.Printf("(store=%v worst=%v cpu=%v writes=%v bytes=%v node=%v high_disk=%v frac_pending=%.2f,%.2f(%t))",
-		sls.sls, sls.worstDim, sls.dimSummary[CPURate], sls.dimSummary[WriteBandwidth], sls.dimSummary[ByteSize],
-		sls.nls, sls.highDiskSpaceUtilization, sls.maxFractionPendingIncrease,
-		sls.maxFractionPendingDecrease,
-		sls.maxFractionPendingIncrease < epsilon && sls.maxFractionPendingDecrease < epsilon)
-}
-
 // The allocator often needs mean load information for a set of stores. This
 // set is implied by a constraintsDisj. We also want to know the set of stores
 // that satisfy that contraintsDisj. meansForStoreSet encapsulates all of this
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go b/pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go
new file mode 100644
index 000000000000..9b5eeaeb2ec4
--- /dev/null
+++ b/pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go
@@ -0,0 +1,31 @@
+// Copyright 2025 The Cockroach Authors.
+//
+// Use of this software is governed by the CockroachDB Software License
+// included in the /LICENSE file.
+
+package mmaprototype
+
+import "github.com/cockroachdb/redact"
+
+type storeLoadSummary struct {
+	worstDim                                               LoadDimension // for logging only
+	sls                                                    loadSummary
+	nls                                                    loadSummary
+	dimSummary                                             [NumLoadDimensions]loadSummary
+	highDiskSpaceUtilization                               bool
+	maxFractionPendingIncrease, maxFractionPendingDecrease float64
+
+	loadSeqNum uint64
+}
+
+func (sls storeLoadSummary) String() string {
+	return redact.StringWithoutMarkers(sls)
+}
+
+func (sls storeLoadSummary) SafeFormat(w redact.SafePrinter, _ rune) {
+	w.Printf("(store=%v worst=%v cpu=%v writes=%v bytes=%v node=%v high_disk=%v frac_pending=%.2f,%.2f(%t))",
+		sls.sls, sls.worstDim, sls.dimSummary[CPURate], sls.dimSummary[WriteBandwidth], sls.dimSummary[ByteSize],
+		sls.nls, sls.highDiskSpaceUtilization, sls.maxFractionPendingIncrease,
+		sls.maxFractionPendingDecrease,
+		sls.maxFractionPendingIncrease < epsilon && sls.maxFractionPendingDecrease < epsilon)
+}

From c0ea6d4bf8e487a4aaebec07d77f2aa2b7615362 Mon Sep 17 00:00:00 2001
From: Tobias Grieger <tobias.b.grieger@gmail.com>
Date: Wed, 5 Nov 2025 13:28:36 +0100
Subject: [PATCH 7/9] mmaprototype: add comment to storeLoadSummary

---
 pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go b/pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go
index 9b5eeaeb2ec4..fe54469c6325 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go
@@ -7,6 +7,10 @@ package mmaprototype
 
 import "github.com/cockroachdb/redact"
 
+// A storeLoadSummary is a classification of a store's load relative to the mean
+// load across a set of permissible stores (often, all that satisfy the
+// constraints for a given range). Sources and targets are primarily picked
+// based on the store- and node level load summaries contained in this struct.
 type storeLoadSummary struct {
 	worstDim                                               LoadDimension // for logging only
 	sls                                                    loadSummary

From 5e46b67e2dda8fbe45011856c1a3a56f6d4bdb47 Mon Sep 17 00:00:00 2001
From: Tobias Grieger <tobias.b.grieger@gmail.com>
Date: Thu, 6 Nov 2025 13:46:08 +0100
Subject: [PATCH 8/9] mmaprototype: remove RemoveNodeAndStores

It is unused and unclear what it would be used for.
Easy to re-add should a need emerge.
---
 pkg/kv/kvserver/allocator/mmaprototype/allocator.go       | 4 ----
 pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go | 7 -------
 2 files changed, 11 deletions(-)

diff --git a/pkg/kv/kvserver/allocator/mmaprototype/allocator.go b/pkg/kv/kvserver/allocator/mmaprototype/allocator.go
index 02c032b9d4b7..c862606ce733 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/allocator.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/allocator.go
@@ -39,10 +39,6 @@ type Allocator interface {
 	// about the nodes in the cluster is a side effect of this method.
 	SetStore(store StoreAttributesAndLocality)
 
-	// RemoveNodeAndStores tells the allocator to remove the NodeID and all its
-	// stores.
-	RemoveNodeAndStores(nodeID roachpb.NodeID) error
-
 	// ProcessStoreLoadMsg provides frequent the state of every store and its
 	// associated node in the cluster.
 	ProcessStoreLoadMsg(ctx context.Context, msg *StoreLoadMsg)
diff --git a/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go b/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go
index 6f3e4301fc78..7a1c28d8288f 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/allocator_state.go
@@ -808,13 +808,6 @@ func (a *allocatorState) SetStore(store StoreAttributesAndLocality) {
 	a.cs.setStore(store)
 }
 
-// RemoveNodeAndStores implements the Allocator interface.
-func (a *allocatorState) RemoveNodeAndStores(nodeID roachpb.NodeID) error {
-	a.mu.Lock()
-	defer a.mu.Unlock()
-	panic("unimplemented")
-}
-
 // ProcessStoreLeaseholderMsg implements the Allocator interface.
 func (a *allocatorState) ProcessStoreLoadMsg(ctx context.Context, msg *StoreLoadMsg) {
 	a.mu.Lock()

From 4822f99913b31c806b9049baea74e0998008e543 Mon Sep 17 00:00:00 2001
From: Tobias Grieger <tobias.b.grieger@gmail.com>
Date: Thu, 6 Nov 2025 13:47:00 +0100
Subject: [PATCH 9/9] mmaprototype: fix typo

---
 pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go b/pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go
index fe54469c6325..10b6c32c7487 100644
--- a/pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go
+++ b/pkg/kv/kvserver/allocator/mmaprototype/store_load_summary.go
@@ -10,7 +10,7 @@ import "github.com/cockroachdb/redact"
 // A storeLoadSummary is a classification of a store's load relative to the mean
 // load across a set of permissible stores (often, all that satisfy the
 // constraints for a given range). Sources and targets are primarily picked
-// based on the store- and node level load summaries contained in this struct.
+// based on the store and node level load summaries contained in this struct.
 type storeLoadSummary struct {
 	worstDim                                               LoadDimension // for logging only
 	sls                                                    loadSummary