unistore: use location cache to reduce the syscall (#54098)

close #54097

pkg/store/mockstore/unistore/cophandler/cop_handler.go

@@ -19,6 +19,7 @@ import (
 	"context"
 	"fmt"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/golang/protobuf/proto"
@@ -50,6 +51,32 @@ import (
 	"github.com/pingcap/tipb/go-tipb"
 )
 
+var globalLocationMap *locationMap = newLocationMap()
+
+type locationMap struct {
+	lmap map[string]*time.Location
+	mu   sync.RWMutex
+}
+
+func newLocationMap() *locationMap {
+	return &locationMap{
+		lmap: make(map[string]*time.Location),
+	}
+}
+
+func (l *locationMap) getLocation(name string) (*time.Location, bool) {
+	l.mu.RLock()
+	defer l.mu.RUnlock()
+	result, ok := l.lmap[name]
+	return result, ok
+}
+
+func (l *locationMap) setLocation(name string, value *time.Location) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	l.lmap[name] = value
+}
+
 // MPPCtx is the mpp execution context
 type MPPCtx struct {
 	RPCClient   client.Client
@@ -309,9 +336,14 @@ func buildDAG(reader *dbreader.DBReader, lockStore *lockstore.MemStore, req *cop
 	case "System":
 		tz = time.Local
 	default:
-		tz, err = time.LoadLocation(dagReq.TimeZoneName)
-		if err != nil {
-			return nil, nil, errors.Trace(err)
+		var ok bool
+		tz, ok = globalLocationMap.getLocation(dagReq.TimeZoneName)
+		if !ok {
+			tz, err = time.LoadLocation(dagReq.TimeZoneName)
+			if err != nil {
+				return nil, nil, errors.Trace(err)
+			}
+			globalLocationMap.setLocation(dagReq.TimeZoneName, tz)
 		}
 	}
 	sctx := flagsAndTzToSessionContext(dagReq.Flags, tz)