resource group: starter mode support degrade to default RU group

DEPS.bzl

@@ -4207,8 +4207,8 @@ def go_deps():
         build_tags = ["nextgen", "intest"],
         build_file_proto_mode = "disable_global",
         importpath = "github.com/tikv/pd/client",
-        sum = "h1:OoBvgoeWmdNEXtS+eOlhysz/OvhA4GS0OdPVhTXteGA=",
-        version = "v0.0.0-20260708075407-4e05b9d2c2d3",
+        sum = "h1:BiPn4oLXVqB9ptPNmyo3rh/2IH1dTouXrrnneH86Z3M=",
+        version = "v0.0.0-20260720043438-0b37df9a48ed",
     )
     go_repository(
         name = "com_github_timakin_bodyclose",

cmd/tidb-server/main.go

@@ -710,6 +710,9 @@ func overrideConfig(cfg *config.Config, fset *flag.FlagSet) {
 	fset.Visit(func(f *flag.Flag) {
 		actualFlags[f.Name] = true
 	})
+	if actualFlags[nmStarterParams] && cfg.DeployMode == deploymode.Starter {
+		terror.MustNil(applyStarterAdditionalParams(cfg, getStarterAdditionalParams()))
+	}
 
 	// Base
 	if actualFlags[nmHost] {
@@ -1352,6 +1355,7 @@ type starterParams struct {
 	podName          string
 	podIP            string
 	podNamespace     string
+	enableRGFallback bool
 }
 
 func parseStarterAdditionalParams(raw string) (starterParams, error) {
@@ -1394,13 +1398,28 @@ func parseStarterAdditionalParams(raw string) (starterParams, error) {
 			params.podIP = value
 		case "pod-namespace":
 			params.podNamespace = value
+		case "enable-rg-fallback":
+			enable, err := strconv.ParseBool(value)
+			if err != nil {
+				return params, fmt.Errorf("starter additional param %q must be a bool: %w", key, err)
+			}
+			params.enableRGFallback = enable
 		default:
 			return params, fmt.Errorf("unknown starter additional param %q", key)
 		}
 	}
 	return params, nil
 }
 
+func applyStarterAdditionalParams(cfg *config.Config, raw string) error {
+	params, err := parseStarterAdditionalParams(raw)
+	if err != nil {
+		return err
+	}
+	cfg.StarterParams.EnableRGFallback = params.enableRGFallback
+	return nil
+}
+
 func getStarterAdditionalParams() string {
 	if starterAdditionalParams == nil {
 		return ""

cmd/tidb-server/main_test.go

@@ -85,13 +85,15 @@ func TestOverrideConfigKeyspaceActivateMode(t *testing.T) {
 	fset := initFlagSet()
 	require.NoError(t, fset.Parse([]string{
 		"--keyspace-activate=true",
-		"--starter-additional-params=pod-name=pod-1,pod-ip=10.0.0.1,pod-namespace=ns-1",
+		"--starter-additional-params=pod-name=pod-1,pod-ip=10.0.0.1,pod-namespace=ns-1,enable-rg-fallback=true",
 	}))
 
 	cfg := config.NewConfig()
+	cfg.DeployMode = deploymode.Starter
 	overrideConfig(cfg, fset)
 	require.True(t, cfg.KeyspaceActivateMode)
-	require.Equal(t, "pod-name=pod-1,pod-ip=10.0.0.1,pod-namespace=ns-1", *starterAdditionalParams)
+	require.True(t, cfg.StarterParams.EnableRGFallback)
+	require.Equal(t, "pod-name=pod-1,pod-ip=10.0.0.1,pod-namespace=ns-1,enable-rg-fallback=true", *starterAdditionalParams)
 }
 
 func TestSetGlobalVars(t *testing.T) {
@@ -217,6 +219,11 @@ func TestCreateMgrClientRequiresPodIdentityInStarter(t *testing.T) {
 	_, err = createMgrClientForStarter()
 	require.ErrorContains(t, err, `unknown starter additional param "unknown"`)
 
+	invalidBoolParam := "enable-rg-fallback=definitely"
+	starterAdditionalParams = &invalidBoolParam
+	_, err = createMgrClientForStarter()
+	require.ErrorContains(t, err, `starter additional param "enable-rg-fallback" must be a bool`)
+
 	config.UpdateGlobal(func(conf *config.Config) {
 		conf.StarterParams.ManagerAddr = ""
 	})

go.mod

@@ -123,7 +123,7 @@ require (
 	github.com/stretchr/testify v1.11.1
 	github.com/tiancaiamao/appdash v0.0.0-20181126055449-889f96f722a2
 	github.com/tikv/client-go/v2 v2.0.8-0.20260708122311-01bd8f99f4da
-	github.com/tikv/pd/client v0.0.0-20260708075407-4e05b9d2c2d3
+	github.com/tikv/pd/client v0.0.0-20260720043438-0b37df9a48ed
 	github.com/timakin/bodyclose v0.0.0-20241222091800-1db5c5ca4d67
 	github.com/twmb/murmur3 v1.1.6
 	github.com/uber/jaeger-client-go v2.22.1+incompatible

go.sum

@@ -902,8 +902,8 @@ github.com/tidwall/sjson v1.2.5 h1:kLy8mja+1c9jlljvWTlSazM7cKDRfJuR/bOJhcY5NcY=
 github.com/tidwall/sjson v1.2.5/go.mod h1:Fvgq9kS/6ociJEDnK0Fk1cpYF4FIW6ZF7LAe+6jwd28=
 github.com/tikv/client-go/v2 v2.0.8-0.20260708122311-01bd8f99f4da h1:Ju9uUKu3M5gPl7Z90e9dcGSe8LtXxGqvSetbPcr6tyc=
 github.com/tikv/client-go/v2 v2.0.8-0.20260708122311-01bd8f99f4da/go.mod h1:MRhIujZMMkYcI49Euif4+A3+SHSGwTpyUUadNz48R4g=
-github.com/tikv/pd/client v0.0.0-20260708075407-4e05b9d2c2d3 h1:OoBvgoeWmdNEXtS+eOlhysz/OvhA4GS0OdPVhTXteGA=
-github.com/tikv/pd/client v0.0.0-20260708075407-4e05b9d2c2d3/go.mod h1:3/Bu91CJONgkDA+Y0v/cnbROSJnu5tQ09vv7JGybUBA=
+github.com/tikv/pd/client v0.0.0-20260720043438-0b37df9a48ed h1:BiPn4oLXVqB9ptPNmyo3rh/2IH1dTouXrrnneH86Z3M=
+github.com/tikv/pd/client v0.0.0-20260720043438-0b37df9a48ed/go.mod h1:3/Bu91CJONgkDA+Y0v/cnbROSJnu5tQ09vv7JGybUBA=
 github.com/timakin/bodyclose v0.0.0-20241222091800-1db5c5ca4d67 h1:9LPGD+jzxMlnk5r6+hJnar67cgpDIz/iyD+rfl5r2Vk=
 github.com/timakin/bodyclose v0.0.0-20241222091800-1db5c5ca4d67/go.mod h1:mkjARE7Yr8qU23YcGMSALbIxTQ9r9QBVahQOBRfU460=
 github.com/tjfoc/gmsm v1.3.2/go.mod h1:HaUcFuY0auTiaHB9MHFGCPx5IaLhTUd2atbCFBQXn9w=

pkg/config/config.go

@@ -1094,6 +1094,9 @@ type StarterParams struct {
 	// ManagerAddr is the TiDB manager address used by the shutdown notifier.
 	// When empty and EnableManagerNotifier is true, the Starter path derives the service address from starter additional params.
 	ManagerAddr string `toml:"manager-addr" json:"manager-addr,omitempty"`
+	// EnableRGFallback enables resource group lookup fallback for resource control.
+	// It is populated from --starter-additional-params and is not file-backed config.
+	EnableRGFallback bool `toml:"-" json:"-"`
 	// MaxImportDataSize is the maximum total real source data size allowed for IMPORT INTO.
 	// Zero means unlimited.
 	MaxImportDataSize configtypes.ByteSize `toml:"max-import-data-size" json:"max-import-data-size,omitempty"`

pkg/domain/BUILD.bazel

@@ -11,6 +11,7 @@ go_library(
         "optimize_trace.go",
         "plan_replayer.go",
         "plan_replayer_dump.go",
+        "resource_group_controller_options.go",
         "ru_stats.go",
         "runaway.go",
         "schema_checker.go",
@@ -116,6 +117,7 @@ go_library(
         "@com_github_pingcap_failpoint//:failpoint",
         "@com_github_pingcap_kvproto//pkg/metapb",
         "@com_github_pingcap_kvproto//pkg/pdpb",
+        "@com_github_pingcap_kvproto//pkg/resource_manager",
         "@com_github_pingcap_log//:log",
         "@com_github_pingcap_metering_sdk//config",
         "@com_github_stretchr_testify//require",
@@ -149,14 +151,17 @@ go_test(
         "plan_replayer_slow_log_test.go",
         "plan_replayer_test.go",
         "ru_stats_test.go",
+        "runaway_test.go",
         "schema_checker_test.go",
         "topn_slow_query_test.go",
     ],
     embed = [":domain"],
     flaky = True,
-    shard_count = 30,
+    shard_count = 33,
     deps = [
         "//pkg/config",
+        "//pkg/config/deploymode",
+        "//pkg/config/kerneltype",
         "//pkg/ddl",
         "//pkg/domain/infosync",
         "//pkg/domain/serverinfo",
@@ -174,6 +179,7 @@ go_test(
         "//pkg/parser/mysql",
         "//pkg/parser/terror",
         "//pkg/planner/extstore",
+        "//pkg/resourcegroup/runaway",
         "//pkg/server",
         "//pkg/session",
         "//pkg/sessionctx/vardef",
@@ -191,15 +197,21 @@ go_test(
         "@com_github_ngaut_pools//:pools",
         "@com_github_pingcap_errors//:errors",
         "@com_github_pingcap_failpoint//:failpoint",
+        "@com_github_pingcap_kvproto//pkg/kvrpcpb",
+        "@com_github_pingcap_kvproto//pkg/meta_storagepb",
         "@com_github_pingcap_kvproto//pkg/metapb",
         "@com_github_pingcap_kvproto//pkg/resource_manager",
         "@com_github_prometheus_client_model//go",
         "@com_github_stretchr_testify//require",
+        "@com_github_tikv_client_go_v2//tikvrpc",
         "@com_github_tikv_client_go_v2//txnkv/transaction",
         "@com_github_tikv_pd_client//:client",
+        "@com_github_tikv_pd_client//errs",
         "@com_github_tikv_pd_client//opt",
         "@com_github_tikv_pd_client//resource_group/controller",
         "@io_etcd_go_etcd_tests_v3//integration",
+        "@org_golang_google_grpc//codes",
+        "@org_golang_google_grpc//status",
         "@org_uber_go_goleak//:goleak",
     ],
 )

pkg/domain/infosync/resource_manager_client.go

@@ -148,6 +148,14 @@ func (*mockResourceManagerClient) LoadResourceGroups(context.Context) ([]*rmpb.R
 	return nil, 0, nil
 }
 
+func (*mockResourceManagerClient) Get(context.Context, []byte, ...opt.MetaStorageOption) (*meta_storagepb.GetResponse, error) {
+	return &meta_storagepb.GetResponse{Header: &meta_storagepb.ResponseHeader{}}, nil
+}
+
+func (*mockResourceManagerClient) Put(context.Context, []byte, []byte, ...opt.MetaStorageOption) (*meta_storagepb.PutResponse, error) {
+	return &meta_storagepb.PutResponse{Header: &meta_storagepb.ResponseHeader{}}, nil
+}
+
 func (m *mockResourceManagerClient) Watch(_ context.Context, key []byte, _ ...opt.MetaStorageOption) (chan *metastorage.WatchResponse, error) {
 	if bytes.Equal(pd.GroupSettingsPathPrefixBytes(m.keyspaceID), key) {
 		return m.eventCh, nil

pkg/domain/resource_group_controller_options.go

@@ -0,0 +1,66 @@
+// Copyright 2026 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package domain
+
+import (
+	"time"
+
+	rmpb "github.com/pingcap/kvproto/pkg/resource_manager"
+	"github.com/pingcap/tidb/pkg/config"
+	"github.com/pingcap/tidb/pkg/config/deploymode"
+	"github.com/pingcap/tidb/pkg/resourcegroup/runaway"
+	rmclient "github.com/tikv/pd/client/resource_group/controller"
+)
+
+const (
+	defaultDegradedRUFillRate      = 2_000_000
+	defaultDegradedRUBurstLimit    = 50_000_000_000
+	defaultDegradedModeWaitTimeout = 3 * time.Second / 2
+	tokenWaitRetryInterval         = 100 * time.Millisecond
+	tokenWaitRetryTimes            = 20
+)
+
+func newDefaultDegradedRUSettings() *rmpb.GroupRequestUnitSettings {
+	return &rmpb.GroupRequestUnitSettings{
+		RU: &rmpb.TokenBucket{
+			Settings: &rmpb.TokenLimitSettings{
+				FillRate:   defaultDegradedRUFillRate,
+				BurstLimit: defaultDegradedRUBurstLimit,
+			},
+		},
+	}
+}
+
+func newResourceGroupsControllerOptions() []rmclient.ResourceControlCreateOption {
+	opts := []rmclient.ResourceControlCreateOption{
+		rmclient.WithMaxWaitDuration(runaway.MaxWaitDuration),
+	}
+	if deploymode.IsStarter() && config.GetGlobalConfig().StarterParams.EnableRGFallback {
+		opts = append(opts,
+			// This Starter-only fallback path is a best-effort UX fallback for
+			// temporary GetResourceGroup failures. It provides a permissive
+			// group so user requests do not fail immediately; it is not intended
+			// to define a precise cross-RPC RU limit or response-side accounting
+			// contract while resource manager is unavailable. Keep synthesis
+			// inside the controller so degraded groups are not inserted into the
+			// normal metadata cache.
+			rmclient.WithDegradedRUSettings(newDefaultDegradedRUSettings()),
+			rmclient.WithDegradedModeWaitDuration(defaultDegradedModeWaitTimeout),
+			rmclient.WithWaitRetryInterval(tokenWaitRetryInterval),
+			rmclient.WithWaitRetryTimes(tokenWaitRetryTimes),
+		)
+	}
+	return opts
+}

pkg/domain/runaway.go

@@ -39,7 +39,7 @@ func (do *Domain) initResourceGroupsController(ctx context.Context, pdClient pd.
 	if codec := do.Store().GetCodec(); codec != nil {
 		keyspaceID = uint32(codec.GetKeyspaceID())
 	}
-	control, err := rmclient.NewResourceGroupController(ctx, uniqueID, pdClient, nil, keyspaceID, rmclient.WithMaxWaitDuration(runaway.MaxWaitDuration))
+	control, err := rmclient.NewResourceGroupController(ctx, uniqueID, pdClient, nil, keyspaceID, newResourceGroupsControllerOptions()...)
 	if err != nil {
 		return err
 	}