add flag for setting join concurrency. (pingcap#1619)

plan/physical_plan_builder.go

@@ -32,6 +32,9 @@ const (
 	cpuFactor       = 0.9
 )
 
+// JoinConcurrency means the number of goroutines that participate joining.
+var JoinConcurrency = 5
+
 func getRowCountByIndexRange(table *statistics.Table, indexRange *IndexRange, indexInfo *model.IndexInfo) (uint64, error) {
 	count := float64(table.Count)
 	for i := 0; i < len(indexRange.LowVal); i++ {
@@ -302,7 +305,7 @@ func (p *Join) handleLeftJoin(prop requiredProperty, innerJoin bool) (*physicalP
 		OtherConditions: p.OtherConditions,
 		SmallTable:      1,
 		// TODO: decide concurrency by data size.
-		Concurrency: 5,
+		Concurrency: JoinConcurrency,
 	}
 	join.SetSchema(p.schema)
 	if innerJoin {
@@ -344,7 +347,7 @@ func (p *Join) handleRightJoin(prop requiredProperty, innerJoin bool) (*physical
 		RightConditions: p.RightConditions,
 		OtherConditions: p.OtherConditions,
 		// TODO: decide concurrency by data size.
-		Concurrency: 5,
+		Concurrency: JoinConcurrency,
 	}
 	join.SetSchema(p.schema)
 	if innerJoin {

tidb-server/main.go

@@ -28,6 +28,7 @@ import (
 	"github.com/pingcap/tidb"
 	"github.com/pingcap/tidb/metric"
 	"github.com/pingcap/tidb/perfschema"
+	"github.com/pingcap/tidb/plan"
 	"github.com/pingcap/tidb/server"
 	"github.com/pingcap/tidb/store/localstore/boltdb"
 	"github.com/pingcap/tidb/store/tikv"
@@ -46,6 +47,7 @@ var (
 	enablePS     = flag.Bool("perfschema", false, "If enable performance schema.")
 	reportStatus = flag.Bool("report-status", true, "If enable status report HTTP service.")
 	logFile      = flag.String("log-file", "", "log file path")
+	joinCon      = flag.Int("join-concurrency", 5, "the number of goroutines that participate joining.")
 )
 
 func main() {
@@ -79,6 +81,10 @@ func main() {
 		}
 		log.SetRotateByDay()
 	}
+
+	if joinCon != nil && *joinCon > 0 {
+		plan.JoinConcurrency = *joinCon
+	}
 	// Call this before setting log level to make sure that TiDB info could be printed.
 	printer.PrintTiDBInfo()
 	log.SetLevelByString(cfg.LogLevel)