*: Add sysvar tidb_tso_client_rpc_mode for setting TSO RPC concurrency

go.mod

@@ -319,6 +319,7 @@ require (
 replace (
 	github.com/go-ldap/ldap/v3 => github.com/YangKeao/ldap/v3 v3.4.5-0.20230421065457-369a3bab1117
 	github.com/pingcap/tidb/pkg/parser => ./pkg/parser
+	github.com/tikv/pd/client => github.com/MyonKeminta/pd/client v0.0.0-20240925045805-0bfe9a69293d
 
 	// TODO: `sourcegraph.com/sourcegraph/appdash` has been archived, and the original host has been removed.
 	// Please remove these dependencies.

go.sum

@@ -80,6 +80,8 @@ github.com/Masterminds/semver/v3 v3.2.1 h1:RN9w6+7QoMeJVGyfmbcgs28Br8cvmnucEXnY0
 github.com/Masterminds/semver/v3 v3.2.1/go.mod h1:qvl/7zhW3nngYb5+80sSMF+FG2BjYrf8m9wsX0PNOMQ=
 github.com/Masterminds/sprig/v3 v3.2.2 h1:17jRggJu518dr3QaafizSXOjKYp94wKfABxUmyxvxX8=
 github.com/Masterminds/sprig/v3 v3.2.2/go.mod h1:UoaO7Yp8KlPnJIYWTFkMaqPUYKTfGFPhxNuwnnxkKlk=
+github.com/MyonKeminta/pd/client v0.0.0-20240925045805-0bfe9a69293d h1:8HHuVEu7PvaTv5wx+m8RqY/X5X/7gd9q79lFb2iU17w=
+github.com/MyonKeminta/pd/client v0.0.0-20240925045805-0bfe9a69293d/go.mod h1:uBHhxAM/SPCMabt483gI/pN/+JXIMKYXohK96s+PwT8=
 github.com/VividCortex/ewma v1.1.1/go.mod h1:2Tkkvm3sRDVXaiyucHiACn4cqf7DpdyLvmxzcbUokwA=
 github.com/VividCortex/ewma v1.2.0 h1:f58SaIzcDXrSy3kWaHNvuJgJ3Nmz59Zji6XoJR/q1ow=
 github.com/VividCortex/ewma v1.2.0/go.mod h1:nz4BbCtbLyFDeC9SUHbtcT5644juEuWfUAUnGx7j5l4=
@@ -824,8 +826,6 @@ github.com/tidwall/btree v1.7.0 h1:L1fkJH/AuEh5zBnnBbmTwQ5Lt+bRJ5A8EWecslvo9iI=
 github.com/tidwall/btree v1.7.0/go.mod h1:twD9XRA5jj9VUQGELzDO4HPQTNJsoWWfYEL+EUQ2cKY=
 github.com/tikv/client-go/v2 v2.0.8-0.20240911041506-e7894a7b27ba h1:dwuuYqPYxU0xcv0bnDgT7I4btQ5c3joBG1HmNOhCTdo=
 github.com/tikv/client-go/v2 v2.0.8-0.20240911041506-e7894a7b27ba/go.mod h1:4HDOAx8OXAJPtqhCZ03IhChXgaFs4B3+vSrPWmiPxjg=
-github.com/tikv/pd/client v0.0.0-20240914083230-71f6f96816e9 h1:J9LChGMzo95eBrjE03NHITDWgxfPgskH+QrCnlW61/Y=
-github.com/tikv/pd/client v0.0.0-20240914083230-71f6f96816e9/go.mod h1:uBHhxAM/SPCMabt483gI/pN/+JXIMKYXohK96s+PwT8=
 github.com/timakin/bodyclose v0.0.0-20240125160201-f835fa56326a h1:A6uKudFIfAEpoPdaal3aSqGxBzLyU8TqyXImLwo6dIo=
 github.com/timakin/bodyclose v0.0.0-20240125160201-f835fa56326a/go.mod h1:mkjARE7Yr8qU23YcGMSALbIxTQ9r9QBVahQOBRfU460=
 github.com/tklauser/go-sysconf v0.3.9/go.mod h1:11DU/5sG7UexIrp/O6g35hrWzu0JxlwQ3LSFUzyeuhs=

pkg/domain/domain_sysvars.go

@@ -83,6 +83,24 @@ func (do *Domain) setPDClientDynamicOption(name, sVal string) error {
 			return err
 		}
 		variable.EnablePDFollowerHandleRegion.Store(val)
+	case variable.TiDBTSOClientRPCMode:
+		var concurrency int
+
+		switch sVal {
+		case variable.TSOClientRPCModeDefault:
+			concurrency = 1
+		case variable.TSOClientRPCModeParallel:
+			concurrency = 2
+		case variable.TSOClientRPCModeParallelFast:
+			concurrency = 4
+		default:
+			return variable.ErrWrongValueForVar.GenWithStackByArgs(name, sVal)
+		}
+
+		err := do.updatePDClient(pd.TSOClientRPCConcurrency, concurrency)
+		if err != nil {
+			return err
+		}
 	}
 	return nil
 }

pkg/sessionctx/variable/sysvar.go

@@ -3383,6 +3383,11 @@ var defaultSysVars = []*SysVar{
 		s.SharedLockPromotion = TiDBOptOn(val)
 		return nil
 	}},
+	{Scope: ScopeGlobal, Name: TiDBTSOClientRPCMode, Value: DefTiDBTSOClientRPCMode, Type: TypeEnum, PossibleValues: []string{TSOClientRPCModeDefault, TSOClientRPCModeParallel, TSOClientRPCModeParallelFast},
+		SetGlobal: func(_ context.Context, s *SessionVars, val string) error {
+			return (*SetPDClientDynamicOption.Load())(TiDBTSOClientRPCMode, val)
+		},
+	},
 }
 
 // GlobalSystemVariableInitialValue gets the default value for a system variable including ones that are dynamically set (e.g. based on the store)

pkg/sessionctx/variable/tidb_vars.go

@@ -1212,6 +1212,9 @@ const (
 	// TiDBEnableLazyCursorFetch defines whether to enable the lazy cursor fetch. If it's `OFF`, all results of
 	// of a cursor will be stored in the tidb node in `EXECUTE` command.
 	TiDBEnableLazyCursorFetch = "tidb_enable_lazy_cursor_fetch"
+	// TiDBTSOClientRPCMode controls how the TSO client performs the TSO RPC requests. It internally controls the
+	// concurrency of the RPC. This variable provides an approach to tune the latency of getting timestamps from PD.
+	TiDBTSOClientRPCMode = "tidb_tso_client_rpc_mode"
 )
 
 // TiDB intentional limits
@@ -1560,6 +1563,7 @@ const (
 	DefTiDBEnableLazyCursorFetch                      = false
 	DefOptEnableProjectionPushDown                    = true
 	DefTiDBEnableSharedLockPromotion                  = false
+	DefTiDBTSOClientRPCMode                           = TSOClientRPCModeDefault
 )
 
 // Process global variables.

pkg/sessionctx/variable/variable.go

@@ -83,6 +83,18 @@ const (
 	OOMActionCancel = "CANCEL"
 	// OOMActionLog constants represents the valid action configurations for OOMAction "LOG".
 	OOMActionLog = "LOG"
+
+	// TSOClientRPCModeDefault is a choice of variable TiDBTSOClientRPCMode. In this mode, the TSO client sends batched
+	// TSO requests serially.
+	TSOClientRPCModeDefault = "DEFAULT"
+	// TSOClientRPCModeParallel is a choice of variable TiDBTSOClientRPCMode. In this mode, the TSO client tries to
+	// keep approximately 2 batched TSO requests running in parallel. This option tries to reduce the batch-waiting time
+	// by half, at the expense of about twice the amount of TSO RPC calls.
+	TSOClientRPCModeParallel = "PARALLEL"
+	// TSOClientRPCModeParallelFast is a choice of variable TiDBTSOClientRPCMode. In this mode, the TSO client tries to
+	// keep approximately 4 batched TSO requests running in parallel. This option tries to reduce the batch-waiting time
+	// by 3/4, at the expense of about 4 times the amount of TSO RPC calls.
+	TSOClientRPCModeParallelFast = "PARALLEL-FAST"
 )
 
 // Global config name list.