session: add no register API for using TiDB as a library

domain/domain.go

@@ -655,6 +655,14 @@ func NewDomain(store kv.Storage, ddlLease time.Duration, statsLease time.Duratio
 
 // Init initializes a domain.
 func (do *Domain) Init(ddlLease time.Duration, sysFactory func(*Domain) (pools.Resource, error)) error {
+	if err := do.InitWithNoRegister(ddlLease, sysFactory); err != nil {
+		return err
+	}
+	return do.initInfoSyncer(context.Background())
+}
+
+// InitWithNoRegister initializes a domain, but not register itself to PD.
+func (do *Domain) InitWithNoRegister(ddlLease time.Duration, sysFactory func(*Domain) (pools.Resource, error)) error {
 	perfschema.Init()
 	if ebd, ok := do.store.(tikv.EtcdBackend); ok {
 		if addrs := ebd.EtcdAddrs(); addrs != nil {
@@ -723,10 +731,6 @@ func (do *Domain) Init(ddlLease time.Duration, sysFactory func(*Domain) (pools.R
 	if err != nil {
 		return err
 	}
-	do.info, err = infosync.GlobalInfoSyncerInit(ctx, do.ddl.GetID(), do.etcdClient)
-	if err != nil {
-		return err
-	}
 	err = do.Reload()
 	if err != nil {
 		return err
@@ -741,6 +745,14 @@ func (do *Domain) Init(ddlLease time.Duration, sysFactory func(*Domain) (pools.R
 	}
 	do.wg.Add(1)
 	go do.topNSlowQueryLoop()
+	return nil
+}
+
+func (do *Domain) initInfoSyncer(ctx context.Context) (err error) {
+	do.info, err = infosync.GlobalInfoSyncerInit(ctx, do.ddl.GetID(), do.etcdClient)
+	if err != nil {
+		return
+	}
 
 	do.wg.Add(1)
 	go do.infoSyncerKeeper()

session/tidb.go

@@ -23,6 +23,8 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/ngaut/pools"
+
 	"github.com/opentracing/opentracing-go"
 	"github.com/pingcap/errors"
 	"github.com/pingcap/parser"
@@ -43,9 +45,30 @@ import (
 	"go.uber.org/zap"
 )
 
+type domainInitializer func(
+	dom *domain.Domain,
+	ddlLease time.Duration,
+	sysFactory func(*domain.Domain) (pools.Resource, error),
+) error
+
 type domainMap struct {
 	domains map[string]*domain.Domain
 	mu      sync.Mutex
+	domInit domainInitializer
+}
+
+// NewDomainMap makes a new empty domain map.
+func NewDomainMap() *domainMap {
+	return &domainMap{
+		domains: map[string]*domain.Domain{},
+		domInit: (*domain.Domain).Init,
+	}
+}
+
+// NoRegister tells this map when creating new Domain, don't register this domain to PD.
+// this function is useful when you want to use TiDB as a library instead of server.
+func (dm *domainMap) NoRegister() {
+	dm.domInit = (*domain.Domain).InitWithNoRegister
 }
 
 func (dm *domainMap) Get(store kv.Storage) (d *domain.Domain, err error) {
@@ -75,7 +98,7 @@ func (dm *domainMap) Get(store kv.Storage) (d *domain.Domain, err error) {
 		factory := createSessionFunc(store)
 		sysFactory := createSessionWithDomainFunc(store)
 		d = domain.NewDomain(store, ddlLease, statisticLease, factory)
-		err1 = d.Init(ddlLease, sysFactory)
+		err1 = dm.domInit(d, ddlLease, sysFactory)
 		if err1 != nil {
 			// If we don't clean it, there are some dirty data when retrying the function of Init.
 			d.Close()
@@ -99,9 +122,7 @@ func (dm *domainMap) Delete(store kv.Storage) {
 }
 
 var (
-	domap = &domainMap{
-		domains: map[string]*domain.Domain{},
-	}
+	domap = NewDomainMap()
 	// store.UUID()-> IfBootstrapped
 	storeBootstrapped     = make(map[string]bool)
 	storeBootstrappedLock sync.Mutex
@@ -118,6 +139,13 @@ var (
 	statsLease = int64(3 * time.Second)
 )
 
+// NoRegister tells TiDB don't register itself to PD.
+// Some of TiDB components will use TiDB as a library(instead of server),
+// this function prevents those fake 'TiDB' present on metrics like dashboard.
+func NoRegister() {
+	domap.NoRegister()
+}
+
 // ResetStoreForWithTiKVTest is only used in the test code.
 // TODO: Remove domap and storeBootstrapped. Use store.SetOption() to do it.
 func ResetStoreForWithTiKVTest(store kv.Storage) {