topsql: introduce pub/sub mode

ddl/ddl_worker.go

@@ -468,7 +468,7 @@ func newMetaWithQueueTp(txn kv.Transaction, tp workerType) *meta.Meta {
 }
 
 func (w *worker) setDDLLabelForTopSQL(job *model.Job) {
-	if !variable.TopSQLEnabled() || job == nil {
+	if !variable.TopSQLInstanceEnabled() || job == nil {
 		return
 	}
 

distsql/request_builder.go

@@ -284,7 +284,7 @@ func (builder *RequestBuilder) SetFromInfoSchema(pis interface{}) *RequestBuilde
 
 // SetResourceGroupTag sets the request resource group tag.
 func (builder *RequestBuilder) SetResourceGroupTag(sc *stmtctx.StatementContext) *RequestBuilder {
-	if variable.TopSQLEnabled() {
+	if variable.TopSQLInstanceEnabled() {
 		builder.Request.ResourceGroupTag = sc.GetResourceGroupTag()
 	}
 	return builder

domain/sysvar_cache.go

@@ -182,7 +182,7 @@ func checkEnableServerGlobalVar(name, sVal string) {
 	case variable.TiDBCapturePlanBaseline:
 		variable.CapturePlanBaseline.Set(sVal, false)
 	case variable.TiDBEnableTopSQL:
-		variable.TopSQLVariable.Enable.Store(variable.TiDBOptOn(sVal))
+		// TODO: whether the topsql global variable is enabled or not doesn't affect instance enabled
 	case variable.TiDBTopSQLPrecisionSeconds:
 		var val int64
 		val, err = strconv.ParseInt(sVal, 10, 64)

executor/adapter.go

@@ -309,7 +309,7 @@ func (a *ExecStmt) RebuildPlan(ctx context.Context) (int64, error) {
 }
 
 func (a *ExecStmt) setPlanLabelForTopSQL(ctx context.Context) context.Context {
-	if a.Plan == nil || !variable.TopSQLEnabled() {
+	if a.Plan == nil || !variable.TopSQLInstanceEnabled() {
 		return ctx
 	}
 	vars := a.Ctx.GetSessionVars()

executor/executor.go

@@ -970,7 +970,7 @@ func (e *SelectLockExec) Next(ctx context.Context, req *chunk.Chunk) error {
 func newLockCtx(seVars *variable.SessionVars, lockWaitTime int64) *tikvstore.LockCtx {
 	var planDigest *parser.Digest
 	_, sqlDigest := seVars.StmtCtx.SQLDigest()
-	if variable.TopSQLEnabled() {
+	if variable.TopSQLInstanceEnabled() {
 		_, planDigest = seVars.StmtCtx.GetPlanDigest()
 	}
 	lockCtx := tikvstore.NewLockCtx(seVars.TxnCtx.GetForUpdateTS(), lockWaitTime, seVars.StmtCtx.GetLockWaitStartTime())
@@ -1715,7 +1715,7 @@ func ResetContextOfStmt(ctx sessionctx.Context, s ast.StmtNode) (err error) {
 			goCtx = pprof.WithLabels(goCtx, pprof.Labels("sql", util.QueryStrForLog(prepareStmt.NormalizedSQL)))
 			pprof.SetGoroutineLabels(goCtx)
 		}
-		if variable.TopSQLEnabled() && prepareStmt.SQLDigest != nil {
+		if variable.TopSQLInstanceEnabled() && prepareStmt.SQLDigest != nil {
 			topsql.AttachSQLInfo(goCtx, prepareStmt.NormalizedSQL, prepareStmt.SQLDigest, "", nil, vars.InRestrictedSQL)
 		}
 	}
@@ -1895,7 +1895,7 @@ func FillVirtualColumnValue(virtualRetTypes []*types.FieldType, virtualColumnInd
 }
 
 func setResourceGroupTagForTxn(sc *stmtctx.StatementContext, snapshot kv.Snapshot) {
-	if snapshot != nil && variable.TopSQLEnabled() {
+	if snapshot != nil && variable.TopSQLInstanceEnabled() {
 		snapshot.SetOption(kv.ResourceGroupTag, sc.GetResourceGroupTag())
 	}
 }

executor/executor_test.go

@@ -8653,11 +8653,8 @@ func (s *testResourceTagSuite) TestResourceGroupTag(c *C) {
 	tk.MustExec("create table t(a int, b int, unique index idx(a));")
 	tbInfo := testGetTableByName(c, tk.Se, "test", "t")
 
-	// Enable Top SQL
-	variable.TopSQLVariable.Enable.Store(true)
-	config.UpdateGlobal(func(conf *config.Config) {
-		conf.TopSQL.ReceiverAddress = "mock-agent"
-	})
+	variable.TopSQLVariable.InstanceEnable.Store(true)
+	defer variable.TopSQLVariable.InstanceEnable.Store(false)
 
 	c.Assert(failpoint.Enable("github.com/pingcap/tidb/store/mockstore/unistore/unistoreRPCClientSendHook", `return(true)`), IsNil)
 	defer failpoint.Disable("github.com/pingcap/tidb/store/mockstore/unistore/unistoreRPCClientSendHook")

executor/prepared.go

@@ -194,7 +194,7 @@ func (e *PrepareExec) Next(ctx context.Context, req *chunk.Chunk) error {
 		SchemaVersion: ret.InfoSchema.SchemaMetaVersion(),
 	}
 	normalizedSQL, digest := parser.NormalizeDigest(prepared.Stmt.Text())
-	if variable.TopSQLEnabled() {
+	if variable.TopSQLInstanceEnabled() {
 		ctx = topsql.AttachSQLInfo(ctx, normalizedSQL, digest, "", nil, vars.InRestrictedSQL)
 	}
 

executor/set_test.go

@@ -1441,12 +1441,6 @@ func (s *testSerialSuite) TestSetTopSQLVariables(c *C) {
 	}()
 
 	tk := testkit.NewTestKit(c, s.store)
-	tk.MustExec("set @@global.tidb_enable_top_sql='On';")
-	tk.MustQuery("select @@global.tidb_enable_top_sql;").Check(testkit.Rows("1"))
-	c.Assert(variable.TopSQLVariable.Enable.Load(), IsTrue)
-	tk.MustExec("set @@global.tidb_enable_top_sql='off';")
-	tk.MustQuery("select @@global.tidb_enable_top_sql;").Check(testkit.Rows("0"))
-	c.Assert(variable.TopSQLVariable.Enable.Load(), IsFalse)
 
 	tk.MustExec("set @@global.tidb_top_sql_precision_seconds=2;")
 	tk.MustQuery("select @@global.tidb_top_sql_precision_seconds;").Check(testkit.Rows("2"))

executor/update.go

@@ -271,7 +271,7 @@ func (e *UpdateExec) updateRows(ctx context.Context) (int, error) {
 				txn.GetSnapshot().SetOption(kv.CollectRuntimeStats, e.stats.SnapshotRuntimeStats)
 			}
 		}
-		if variable.TopSQLEnabled() {
+		if variable.TopSQLInstanceEnabled() {
 			txn, err := e.ctx.Txn(true)
 			if err == nil {
 				txn.SetOption(kv.ResourceGroupTag, e.ctx.GetSessionVars().StmtCtx.GetResourceGroupTag())

go.mod

@@ -53,7 +53,7 @@ require (
 	github.com/pingcap/sysutil v0.0.0-20210730114356-fcd8a63f68c5
 	github.com/pingcap/tidb-tools v5.2.2-0.20211019062242-37a8bef2fa17+incompatible
 	github.com/pingcap/tidb/parser v0.0.0-20211011031125-9b13dc409c5e
-	github.com/pingcap/tipb v0.0.0-20211008080435-3fd327dfce0e
+	github.com/pingcap/tipb v0.0.0-20211026032243-186050f116ed
 	github.com/prometheus/client_golang v1.5.1
 	github.com/prometheus/client_model v0.2.0
 	github.com/prometheus/common v0.9.1

go.sum

@@ -614,8 +614,8 @@ github.com/pingcap/tidb-dashboard v0.0.0-20210312062513-eef5d6404638/go.mod h1:O
 github.com/pingcap/tidb-dashboard v0.0.0-20210716172320-2226872e3296/go.mod h1:OCXbZTBTIMRcIt0jFsuCakZP+goYRv6IjawKbwLS2TQ=
 github.com/pingcap/tidb-tools v5.2.2-0.20211019062242-37a8bef2fa17+incompatible h1:c7+izmker91NkjkZ6FgTlmD4k1A5FLOAq+li6Ki2/GY=
 github.com/pingcap/tidb-tools v5.2.2-0.20211019062242-37a8bef2fa17+incompatible/go.mod h1:XGdcy9+yqlDSEMTpOXnwf3hiTeqrV6MN/u1se9N8yIM=
-github.com/pingcap/tipb v0.0.0-20211008080435-3fd327dfce0e h1:fZY5T65QWiPc9noQJ1UkdwejZyBZjNfxzSyTcBjKrEU=
-github.com/pingcap/tipb v0.0.0-20211008080435-3fd327dfce0e/go.mod h1:A7mrd7WHBl1o63LE2bIBGEJMTNWXqhgmYiOvMLxozfs=
+github.com/pingcap/tipb v0.0.0-20211026032243-186050f116ed h1:46eHok6tYe87/+RQCWRzbCnQFlL65K/Nv2Z98LhMl5Y=
+github.com/pingcap/tipb v0.0.0-20211026032243-186050f116ed/go.mod h1:A7mrd7WHBl1o63LE2bIBGEJMTNWXqhgmYiOvMLxozfs=
 github.com/pkg/errors v0.8.0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=

server/conn.go

@@ -1194,7 +1194,7 @@ func (cc *clientConn) dispatch(ctx context.Context, data []byte) error {
 	cc.lastPacket = data
 	cmd := data[0]
 	data = data[1:]
-	if variable.TopSQLEnabled() {
+	if variable.TopSQLInstanceEnabled() {
 		defer pprof.SetGoroutineLabels(ctx)
 	}
 	if variable.EnablePProfSQLCPU.Load() {

server/conn_stmt.go

@@ -127,7 +127,7 @@ func (cc *clientConn) handleStmtExecute(ctx context.Context, data []byte) (err e
 	stmtID := binary.LittleEndian.Uint32(data[0:4])
 	pos += 4
 
-	if variable.TopSQLEnabled() {
+	if variable.TopSQLInstanceEnabled() {
 		preparedStmt, _ := cc.preparedStmtID2CachePreparedStmt(stmtID)
 		if preparedStmt != nil && preparedStmt.SQLDigest != nil {
 			ctx = topsql.AttachSQLInfo(ctx, preparedStmt.NormalizedSQL, preparedStmt.SQLDigest, "", nil, false)
@@ -273,7 +273,7 @@ func (cc *clientConn) handleStmtFetch(ctx context.Context, data []byte) (err err
 		return errors.Annotate(mysql.NewErr(mysql.ErrUnknownStmtHandler,
 			strconv.FormatUint(uint64(stmtID), 10), "stmt_fetch"), cc.preparedStmt2String(stmtID))
 	}
-	if variable.TopSQLEnabled() {
+	if variable.TopSQLInstanceEnabled() {
 		prepareObj, _ := cc.preparedStmtID2CachePreparedStmt(stmtID)
 		if prepareObj != nil && prepareObj.SQLDigest != nil {
 			ctx = topsql.AttachSQLInfo(ctx, prepareObj.NormalizedSQL, prepareObj.SQLDigest, "", nil, false)

server/rpc_server.go

@@ -32,6 +32,7 @@ import (
 	"github.com/pingcap/tidb/util"
 	"github.com/pingcap/tidb/util/logutil"
 	"github.com/pingcap/tidb/util/memory"
+	"github.com/pingcap/tidb/util/topsql"
 	"go.uber.org/zap"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/peer"
@@ -54,6 +55,7 @@ func NewRPCServer(config *config.Config, dom *domain.Domain, sm util.SessionMana
 	}
 	diagnosticspb.RegisterDiagnosticsServer(s, rpcSrv)
 	tikvpb.RegisterTikvServer(s, rpcSrv)
+	topsql.RegisterPubSubServer(s)
 	return s
 }
 

server/tidb_test.go

@@ -1631,6 +1631,8 @@ func (ts *tidbTestTopSQLSuite) TestTopSQLCPUProfile(c *C) {
 		c.Assert(err, IsNil)
 	}()
 
+	variable.TopSQLVariable.InstanceEnable.Store(true)
+	defer variable.TopSQLVariable.InstanceEnable.Store(false)
 	collector := mockTopSQLTraceCPU.NewTopSQLCollector()
 	tracecpu.GlobalSQLCPUProfiler.SetCollector(&collectorWrapper{collector})
 
@@ -1641,7 +1643,6 @@ func (ts *tidbTestTopSQLSuite) TestTopSQLCPUProfile(c *C) {
 	dbt.mustExec("create table t (a int auto_increment, b int, unique index idx(a));")
 	dbt.mustExec("create table t1 (a int auto_increment, b int, unique index idx(a));")
 	dbt.mustExec("create table t2 (a int auto_increment, b int, unique index idx(a));")
-	dbt.mustExec("set @@global.tidb_enable_top_sql='On';")
 	config.UpdateGlobal(func(conf *config.Config) {
 		conf.TopSQL.ReceiverAddress = "127.0.0.1:4001"
 	})
@@ -1837,18 +1838,18 @@ func (ts *tidbTestTopSQLSuite) TestTopSQLCPUProfile(c *C) {
 	checkFn("commit", "")
 }
 
-func (ts *tidbTestTopSQLSuite) TestTopSQLAgent(c *C) {
+func (ts *tidbTestTopSQLSuite) TestTopSQLReceiver(c *C) {
 	c.Skip("unstable, skip it and fix it before 20210702")
 	db, err := sql.Open("mysql", ts.getDSN())
 	c.Assert(err, IsNil, Commentf("Error connecting"))
 	defer func() {
 		err := db.Close()
 		c.Assert(err, IsNil)
 	}()
-	agentServer, err := mockTopSQLReporter.StartMockAgentServer()
+	receiverServer, err := mockTopSQLReporter.StartMockReceiverServer()
 	c.Assert(err, IsNil)
 	defer func() {
-		agentServer.Stop()
+		receiverServer.Stop()
 	}()
 
 	c.Assert(failpoint.Enable("github.com/pingcap/tidb/util/topsql/reporter/resetTimeoutForTest", `return(true)`), IsNil)
@@ -1878,27 +1879,26 @@ func (ts *tidbTestTopSQLSuite) TestTopSQLAgent(c *C) {
 			conf.TopSQL.ReceiverAddress = addr
 		})
 	}
-	dbt.mustExec("set @@global.tidb_enable_top_sql='On';")
 	setTopSQLReceiverAddress("")
 	dbt.mustExec("set @@global.tidb_top_sql_precision_seconds=1;")
 	dbt.mustExec("set @@global.tidb_top_sql_report_interval_seconds=2;")
 	dbt.mustExec("set @@global.tidb_top_sql_max_statement_count=5;")
 
-	r := reporter.NewRemoteTopSQLReporter(reporter.NewGRPCReportClient(plancodec.DecodeNormalizedPlan))
+	r := reporter.NewRemoteTopSQLReporter(reporter.NewReportClientRegistry(), reporter.NewGRPCReportClient(plancodec.DecodeNormalizedPlan))
 	tracecpu.GlobalSQLCPUProfiler.SetCollector(&collectorWrapper{r})
 
 	// TODO: change to ensure that the right sql statements are reported, not just counts
 	checkFn := func(n int) {
-		records := agentServer.GetLatestRecords()
+		records := receiverServer.GetLatestRecords()
 		c.Assert(len(records), Equals, n)
 		for _, r := range records {
-			sqlMeta, exist := agentServer.GetSQLMetaByDigestBlocking(r.SqlDigest, time.Second)
+			sqlMeta, exist := receiverServer.GetSQLMetaByDigestBlocking(r.SqlDigest, time.Second)
 			c.Assert(exist, IsTrue)
 			c.Check(sqlMeta.NormalizedSql, Matches, "select.*from.*join.*")
 			if len(r.PlanDigest) == 0 {
 				continue
 			}
-			plan, exist := agentServer.GetPlanMetaByDigestBlocking(r.PlanDigest, time.Second)
+			plan, exist := receiverServer.GetPlanMetaByDigestBlocking(r.PlanDigest, time.Second)
 			c.Assert(exist, IsTrue)
 			plan = strings.Replace(plan, "\n", " ", -1)
 			plan = strings.Replace(plan, "\t", " ", -1)
@@ -1923,22 +1923,22 @@ func (ts *tidbTestTopSQLSuite) TestTopSQLAgent(c *C) {
 	cancel := runWorkload(0, 10)
 	// Test with null agent address, the agent server can't receive any record.
 	setTopSQLReceiverAddress("")
-	agentServer.WaitCollectCnt(1, time.Second*4)
+	receiverServer.WaitCollectCnt(1, time.Second*4)
 	checkFn(0)
 	// Test after set agent address and the evict take effect.
 	dbt.mustExec("set @@global.tidb_top_sql_max_statement_count=5;")
-	setTopSQLReceiverAddress(agentServer.Address())
-	agentServer.WaitCollectCnt(1, time.Second*4)
+	setTopSQLReceiverAddress(receiverServer.Address())
+	receiverServer.WaitCollectCnt(1, time.Second*4)
 	checkFn(5)
 	// Test with wrong agent address, the agent server can't receive any record.
 	dbt.mustExec("set @@global.tidb_top_sql_max_statement_count=8;")
 	setTopSQLReceiverAddress("127.0.0.1:65530")
 
-	agentServer.WaitCollectCnt(1, time.Second*4)
+	receiverServer.WaitCollectCnt(1, time.Second*4)
 	checkFn(0)
 	// Test after set agent address and the evict take effect.
-	setTopSQLReceiverAddress(agentServer.Address())
-	agentServer.WaitCollectCnt(1, time.Second*4)
+	setTopSQLReceiverAddress(receiverServer.Address())
+	receiverServer.WaitCollectCnt(1, time.Second*4)
 	checkFn(8)
 	cancel() // cancel case 1
 
@@ -1947,44 +1947,44 @@ func (ts *tidbTestTopSQLSuite) TestTopSQLAgent(c *C) {
 	// empty agent address, should not collect records
 	dbt.mustExec("set @@global.tidb_top_sql_max_statement_count=5;")
 	setTopSQLReceiverAddress("")
-	agentServer.WaitCollectCnt(1, time.Second*4)
+	receiverServer.WaitCollectCnt(1, time.Second*4)
 	checkFn(0)
 	// set correct address, should collect records
-	setTopSQLReceiverAddress(agentServer.Address())
-	agentServer.WaitCollectCnt(1, time.Second*4)
+	setTopSQLReceiverAddress(receiverServer.Address())
+	receiverServer.WaitCollectCnt(1, time.Second*4)
 	checkFn(5)
 	// agent server hangs for a while
-	agentServer.HangFromNow(time.Second * 6)
+	receiverServer.HangFromNow(time.Second * 6)
 	// run another set of SQL queries
 	cancel2()
 
 	cancel3 := runWorkload(11, 20)
-	agentServer.WaitCollectCnt(1, time.Second*8)
+	receiverServer.WaitCollectCnt(1, time.Second*8)
 	checkFn(5)
 	cancel3()
 
 	// case 3: agent restart
 	cancel4 := runWorkload(0, 10)
 	// empty agent address, should not collect records
 	setTopSQLReceiverAddress("")
-	agentServer.WaitCollectCnt(1, time.Second*4)
+	receiverServer.WaitCollectCnt(1, time.Second*4)
 	checkFn(0)
 	// set correct address, should collect records
-	setTopSQLReceiverAddress(agentServer.Address())
-	agentServer.WaitCollectCnt(1, time.Second*8)
+	setTopSQLReceiverAddress(receiverServer.Address())
+	receiverServer.WaitCollectCnt(1, time.Second*8)
 	checkFn(5)
 	// run another set of SQL queries
 	cancel4()
 
 	cancel5 := runWorkload(11, 20)
 	// agent server shutdown
-	agentServer.Stop()
+	receiverServer.Stop()
 	// agent server restart
-	agentServer, err = mockTopSQLReporter.StartMockAgentServer()
+	receiverServer, err = mockTopSQLReporter.StartMockReceiverServer()
 	c.Assert(err, IsNil)
-	setTopSQLReceiverAddress(agentServer.Address())
+	setTopSQLReceiverAddress(receiverServer.Address())
 	// check result
-	agentServer.WaitCollectCnt(2, time.Second*8)
+	receiverServer.WaitCollectCnt(2, time.Second*8)
 	checkFn(5)
 	cancel5()
 }

session/session.go

@@ -1268,7 +1268,7 @@ func (s *session) ExecuteInternal(ctx context.Context, sql string, args ...inter
 	s.sessionVars.InRestrictedSQL = true
 	defer func() {
 		s.sessionVars.InRestrictedSQL = origin
-		if variable.TopSQLEnabled() {
+		if variable.TopSQLInstanceEnabled() {
 			//  Restore the goroutine label by using the original ctx after execution is finished.
 			pprof.SetGoroutineLabels(ctx)
 		}
@@ -1408,7 +1408,7 @@ func (s *session) ParseWithParams(ctx context.Context, sql string, args ...inter
 	for _, warn := range warns {
 		s.sessionVars.StmtCtx.AppendWarning(util.SyntaxWarn(warn))
 	}
-	if variable.TopSQLEnabled() {
+	if variable.TopSQLInstanceEnabled() {
 		normalized, digest := parser.NormalizeDigest(sql)
 		if digest != nil {
 			// Reset the goroutine label when internal sql execute finish.
@@ -1422,7 +1422,7 @@ func (s *session) ParseWithParams(ctx context.Context, sql string, args ...inter
 // ExecRestrictedStmt implements RestrictedSQLExecutor interface.
 func (s *session) ExecRestrictedStmt(ctx context.Context, stmtNode ast.StmtNode, opts ...sqlexec.OptionFuncAlias) (
 	[]chunk.Row, []*ast.ResultField, error) {
-	if variable.TopSQLEnabled() {
+	if variable.TopSQLInstanceEnabled() {
 		defer pprof.SetGoroutineLabels(ctx)
 	}
 	var execOption sqlexec.ExecOption
@@ -1530,7 +1530,7 @@ func (s *session) ExecuteStmt(ctx context.Context, stmtNode ast.StmtNode) (sqlex
 		return nil, err
 	}
 	normalizedSQL, digest := s.sessionVars.StmtCtx.SQLDigest()
-	if variable.TopSQLEnabled() {
+	if variable.TopSQLInstanceEnabled() {
 		ctx = topsql.AttachSQLInfo(ctx, normalizedSQL, digest, "", nil, s.sessionVars.InRestrictedSQL)
 	}
 

sessionctx/variable/sysvar.go

@@ -1736,9 +1736,9 @@ var defaultSysVars = []*SysVar{
 	}},
 	// variable for top SQL feature.
 	{Scope: ScopeGlobal, Name: TiDBEnableTopSQL, Value: BoolToOnOff(DefTiDBTopSQLEnable), Type: TypeBool, Hidden: true, AllowEmpty: true, GetGlobal: func(s *SessionVars) (string, error) {
-		return BoolToOnOff(TopSQLVariable.Enable.Load()), nil
+		return Off, nil
 	}, SetGlobal: func(vars *SessionVars, s string) error {
-		TopSQLVariable.Enable.Store(TiDBOptOn(s))
+		// TODO: call pd to enable topsql globally. Not to affect the current instance directly.
 		return nil
 	}},
 	{Scope: ScopeGlobal, Name: TiDBTopSQLPrecisionSeconds, Value: strconv.Itoa(DefTiDBTopSQLPrecisionSeconds), Type: TypeInt, Hidden: true, MinValue: 1, MaxValue: math.MaxInt64, GetGlobal: func(s *SessionVars) (string, error) {