Merge pull request pingcap#4 from PatrickNicholas/2020-hackathon

store: make network cost threshold as a Variable
abbccdda · Jan 16, 2021 · 5fc0756 · 5fc0756
2 parents 40d9bf5 + d5aba00
commit 5fc0756
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Showing 6 changed files with 18 additions and 10 deletions.
diff --git a/kv/variables.go b/kv/variables.go
@@ -27,14 +27,18 @@ type Variables struct {
 	// Pointer to SessionVars.Killed
 	// Killed is a flag to indicate that this query is killed.
 	Killed *uint32
+
+	// AdaptiveFollowerReadCostThreshold specifies the threshold of adpative follower local scan.
+	AdaptiveFollowerReadCostThreshold int
 }
 
 // NewVariables create a new Variables instance with default values.
 func NewVariables(killed *uint32) *Variables {
 	return &Variables{
-		BackoffLockFast: DefBackoffLockFast,
-		BackOffWeight:   DefBackOffWeight,
-		Killed:          killed,
+		BackoffLockFast:                   DefBackoffLockFast,
+		BackOffWeight:                     DefBackOffWeight,
+		Killed:                            killed,
+		AdaptiveFollowerReadCostThreshold: DefAdaptiveFollowerReadThreshold,
 	}
 }
 
@@ -45,6 +49,7 @@ var DefaultVars = NewVariables(&ignoreKill)
 
 // Default values
 const (
-	DefBackoffLockFast = 100
-	DefBackOffWeight   = 2
+	DefAdaptiveFollowerReadThreshold = 4096
+	DefBackoffLockFast               = 100
+	DefBackOffWeight                 = 2
 )
diff --git a/session/session.go b/session/session.go
@@ -2403,6 +2403,7 @@ var builtinGlobalVariable = []string{
 	variable.TiDBExecutorConcurrency,
 	variable.TiDBBackoffLockFast,
 	variable.TiDBBackOffWeight,
+	variable.TiDBAdaptiveFollowerReadThreshold,
 	variable.TiDBConstraintCheckInPlace,
 	variable.TiDBDDLReorgWorkerCount,
 	variable.TiDBDDLReorgBatchSize,

diff --git a/sessionctx/variable/session.go b/sessionctx/variable/session.go
@@ -1444,6 +1444,8 @@ func (s *SessionVars) SetSystemVar(name string, val string) error {
 		s.KVVars.BackoffLockFast = tidbOptPositiveInt32(val, kv.DefBackoffLockFast)
 	case TiDBBackOffWeight:
 		s.KVVars.BackOffWeight = tidbOptPositiveInt32(val, kv.DefBackOffWeight)
+	case TiDBAdaptiveFollowerReadThreshold:
+		s.KVVars.AdaptiveFollowerReadCostThreshold = tidbOptPositiveInt32(val, kv.DefAdaptiveFollowerReadThreshold)
 	case TiDBConstraintCheckInPlace:
 		s.ConstraintCheckInPlace = TiDBOptOn(val)
 	case TiDBBatchInsert:

diff --git a/sessionctx/variable/sysvar.go b/sessionctx/variable/sysvar.go
@@ -638,6 +638,7 @@ var defaultSysVars = []*SysVar{
 	{Scope: ScopeGlobal | ScopeSession, Name: TiDBMemQuotaApplyCache, Value: strconv.Itoa(DefTiDBMemQuotaApplyCache)},
 	{Scope: ScopeGlobal | ScopeSession, Name: TiDBBackoffLockFast, Value: strconv.Itoa(kv.DefBackoffLockFast), Type: TypeUnsigned, MinValue: 1, MaxValue: math.MaxUint64},
 	{Scope: ScopeGlobal | ScopeSession, Name: TiDBBackOffWeight, Value: strconv.Itoa(kv.DefBackOffWeight), Type: TypeUnsigned, MinValue: 1, MaxValue: math.MaxUint64},
+	{Scope: ScopeGlobal | ScopeSession, Name: TiDBAdaptiveFollowerReadThreshold, Value: strconv.Itoa(kv.DefAdaptiveFollowerReadCostThreshold), Type: TypeUnsigned, MinValue: 1, MaxValue: math.MaxUint64}
 	{Scope: ScopeGlobal | ScopeSession, Name: TiDBRetryLimit, Value: strconv.Itoa(DefTiDBRetryLimit), Type: TypeInt, MinValue: -1, MaxValue: math.MaxInt64},
 	{Scope: ScopeGlobal | ScopeSession, Name: TiDBDisableTxnAutoRetry, Value: BoolToOnOff(DefTiDBDisableTxnAutoRetry), Type: TypeBool},
 	{Scope: ScopeGlobal | ScopeSession, Name: TiDBConstraintCheckInPlace, Value: BoolToOnOff(DefTiDBConstraintCheckInPlace), Type: TypeBool},

diff --git a/sessionctx/variable/tidb_vars.go b/sessionctx/variable/tidb_vars.go
@@ -345,6 +345,9 @@ const (
 	// Only positive integers can be accepted, which means that the maximum back off time can only grow.
 	TiDBBackOffWeight = "tidb_backoff_weight"
 
+	// tidb_adaptive_follower_read_threshold is used to determinate whether a scan request should adaptively read local follower.
+	TiDBAdaptiveFollowerReadThreshold = "tidb_adaptive_follower_read_threshold"
+
 	// tidb_ddl_reorg_worker_cnt defines the count of ddl reorg workers.
 	TiDBDDLReorgWorkerCount = "tidb_ddl_reorg_worker_cnt"
 

diff --git a/store/tikv/coprocessor.go b/store/tikv/coprocessor.go
@@ -45,10 +45,6 @@ import (
 	"go.uber.org/zap"
 )
 
-// CostThreshold marks the cost threshold to determine whether given request is
-// a large scan request.
-const CostThreshold = 64 * 1024 // 64KB
-
 var (
 	tikvTxnRegionsNumHistogramWithCoprocessor      = metrics.TiKVTxnRegionsNumHistogram.WithLabelValues("coprocessor")
 	tikvTxnRegionsNumHistogramWithBatchCoprocessor = metrics.TiKVTxnRegionsNumHistogram.WithLabelValues("batch_coprocessor")
@@ -884,7 +880,7 @@ func (worker *copIteratorWorker) handleTaskOnce(bo *Backoffer, task *copTask, ch
 			}
 			networkCost += worker.req.NetworkCostEstimater(&kvRange, worker.req.KeyRanges)
 		}
-		if networkCost > float64(CostThreshold) {
+		if networkCost > float64(worker.vars.AdaptiveFollowerReadCostThreshold) {
 			recommendLocalScan = true
 		}
 	}