storage: plumb AdminChangeReplicas request

Plumbing an `AdminChangeReplicas` request. Refactoring the `testcluster` code
to issue this operation rather than calling into the `Replica` directly.

This request will be used to implement `SCATTER` and `TESTING_RELOCATE`
(cockroachdb#13665).

pkg/internal/client/batch.go

@@ -245,6 +245,7 @@ func (b *Batch) fillResults() error {
 			case *roachpb.AdminMergeRequest:
 			case *roachpb.AdminSplitRequest:
 			case *roachpb.AdminTransferLeaseRequest:
+			case *roachpb.AdminChangeReplicasRequest:
 			case *roachpb.HeartbeatTxnRequest:
 			case *roachpb.GCRequest:
 			case *roachpb.PushTxnRequest:
@@ -608,6 +609,27 @@ func (b *Batch) adminTransferLease(key interface{}, target roachpb.StoreID) {
 	b.initResult(1, 0, notRaw, nil)
 }
 
+// adminChangeReplicas is only exported on DB. It is here for symmetry with the
+// other operations.
+func (b *Batch) adminChangeReplicas(
+	key interface{}, changeType roachpb.ReplicaChangeType, targets []roachpb.ReplicationTarget,
+) {
+	k, err := marshalKey(key)
+	if err != nil {
+		b.initResult(0, 0, notRaw, err)
+		return
+	}
+	req := &roachpb.AdminChangeReplicasRequest{
+		Span: roachpb.Span{
+			Key: k,
+		},
+		ChangeType: changeType,
+		Targets:    targets,
+	}
+	b.appendReqs(req)
+	b.initResult(1, 0, notRaw, nil)
+}
+
 // writeBatch is only exported on DB.
 func (b *Batch) writeBatch(s, e interface{}, data []byte) {
 	begin, err := marshalKey(s)

pkg/internal/client/db.go

@@ -391,6 +391,18 @@ func (db *DB) AdminTransferLease(
 	return getOneErr(db.Run(ctx, b), b)
 }
 
+// AdminChangeReplicas adds or removes a set of replicas for a range.
+func (db *DB) AdminChangeReplicas(
+	ctx context.Context,
+	key interface{},
+	changeType roachpb.ReplicaChangeType,
+	targets []roachpb.ReplicationTarget,
+) error {
+	b := &Batch{}
+	b.adminChangeReplicas(key, changeType, targets)
+	return getOneErr(db.Run(ctx, b), b)
+}
+
 // CheckConsistency runs a consistency check on all the ranges containing
 // the key span. It logs a diff of all the keys that are inconsistent
 // when withDiff is set to true.

pkg/internal/client/db_test.go

@@ -369,6 +369,7 @@ func TestCommonMethods(t *testing.T) {
 		{dbType, "AdminMerge"}:                 {},
 		{dbType, "AdminSplit"}:                 {},
 		{dbType, "AdminTransferLease"}:         {},
+		{dbType, "AdminChangeReplicas"}:        {},
 		{dbType, "CheckConsistency"}:           {},
 		{dbType, "Run"}:                        {},
 		{dbType, "Txn"}:                        {},

pkg/roachpb/api.go

@@ -436,6 +436,9 @@ func (*AdminMergeRequest) Method() Method { return AdminMerge }
 // Method implements the Request interface.
 func (*AdminTransferLeaseRequest) Method() Method { return AdminTransferLease }
 
+// Method implements the Request interface.
+func (*AdminChangeReplicasRequest) Method() Method { return AdminChangeReplicas }
+
 // Method implements the Request interface.
 func (*HeartbeatTxnRequest) Method() Method { return HeartbeatTxn }
 
@@ -586,6 +589,12 @@ func (atlr *AdminTransferLeaseRequest) ShallowCopy() Request {
 	return &shallowCopy
 }
 
+// ShallowCopy implements the Request interface.
+func (acrr *AdminChangeReplicasRequest) ShallowCopy() Request {
+	shallowCopy := *acrr
+	return &shallowCopy
+}
+
 // ShallowCopy implements the Request interface.
 func (htr *HeartbeatTxnRequest) ShallowCopy() Request {
 	shallowCopy := *htr
@@ -863,22 +872,23 @@ func (drr *DeleteRangeRequest) flags() int {
 	}
 	return isWrite | isTxn | isTxnWrite | isRange
 }
-func (*ScanRequest) flags() int               { return isRead | isRange | isTxn }
-func (*ReverseScanRequest) flags() int        { return isRead | isRange | isReverse | isTxn }
-func (*BeginTransactionRequest) flags() int   { return isWrite | isTxn }
-func (*EndTransactionRequest) flags() int     { return isWrite | isTxn | isAlone }
-func (*AdminSplitRequest) flags() int         { return isAdmin | isAlone }
-func (*AdminMergeRequest) flags() int         { return isAdmin | isAlone }
-func (*AdminTransferLeaseRequest) flags() int { return isAdmin | isAlone }
-func (*HeartbeatTxnRequest) flags() int       { return isWrite | isTxn }
-func (*GCRequest) flags() int                 { return isWrite | isRange }
-func (*PushTxnRequest) flags() int            { return isWrite | isAlone }
-func (*QueryTxnRequest) flags() int           { return isRead | isAlone }
-func (*RangeLookupRequest) flags() int        { return isRead }
-func (*ResolveIntentRequest) flags() int      { return isWrite }
-func (*ResolveIntentRangeRequest) flags() int { return isWrite | isRange }
-func (*NoopRequest) flags() int               { return isRead } // slightly special
-func (*TruncateLogRequest) flags() int        { return isWrite | isNonKV }
+func (*ScanRequest) flags() int                { return isRead | isRange | isTxn }
+func (*ReverseScanRequest) flags() int         { return isRead | isRange | isReverse | isTxn }
+func (*BeginTransactionRequest) flags() int    { return isWrite | isTxn }
+func (*EndTransactionRequest) flags() int      { return isWrite | isTxn | isAlone }
+func (*AdminSplitRequest) flags() int          { return isAdmin | isAlone }
+func (*AdminMergeRequest) flags() int          { return isAdmin | isAlone }
+func (*AdminTransferLeaseRequest) flags() int  { return isAdmin | isAlone }
+func (*AdminChangeReplicasRequest) flags() int { return isAdmin | isAlone }
+func (*HeartbeatTxnRequest) flags() int        { return isWrite | isTxn }
+func (*GCRequest) flags() int                  { return isWrite | isRange }
+func (*PushTxnRequest) flags() int             { return isWrite | isAlone }
+func (*QueryTxnRequest) flags() int            { return isRead | isAlone }
+func (*RangeLookupRequest) flags() int         { return isRead }
+func (*ResolveIntentRequest) flags() int       { return isWrite }
+func (*ResolveIntentRangeRequest) flags() int  { return isWrite | isRange }
+func (*NoopRequest) flags() int                { return isRead } // slightly special
+func (*TruncateLogRequest) flags() int         { return isWrite | isNonKV }
 
 // MergeRequests are considered "non KV" because they do not need to be gated
 // by the command queue (reordering is ok) and they operate on non-MVCC data so