statistics: update some vars for internal sessions correctly

Signed-off-by: hi-rustin <rustin.liu@gmail.com>

pkg/statistics/handle/globalstats/global_stats.go

@@ -103,6 +103,7 @@ func MergePartitionStats2GlobalStats(
 	histIDs []int64,
 ) (globalStats *GlobalStats, err error) {
 	if sc.GetSessionVars().EnableAsyncMergeGlobalStats {
+		logutil.BgLogger().Info("use async merge global stats", zap.String("table", globalTableInfo.Name.L))
 		worker, err := NewAsyncMergePartitionStats2GlobalStats(statsHandle, globalTableInfo, histIDs, is)
 		if err != nil {
 			return nil, errors.Trace(err)
@@ -113,6 +114,7 @@ func MergePartitionStats2GlobalStats(
 		}
 		return worker.Result(), nil
 	}
+	logutil.BgLogger().Info("use blocking merge global stats", zap.String("table", globalTableInfo.Name.L))
 	return blockingMergePartitionStats2GlobalStats(sc, statsHandle.GPool(), opts, is, globalTableInfo, isIndex, histIDs, nil, statsHandle)
 }
 

pkg/statistics/handle/util/util.go

@@ -105,6 +105,24 @@ func CallWithSCtx(pool SessionPool, f func(sctx sessionctx.Context) error, flags
 
 // UpdateSCtxVarsForStats updates all necessary variables that may affect the behavior of statistics.
 func UpdateSCtxVarsForStats(sctx sessionctx.Context) error {
+	// async merge global stats
+	enableAsyncMergeGlobalStats, err := sctx.GetSessionVars().GlobalVarsAccessor.GetGlobalSysVar(variable.TiDBEnableAsyncMergeGlobalStats)
+	if err != nil {
+		return err
+	}
+	sctx.GetSessionVars().EnableAsyncMergeGlobalStats = variable.TiDBOptOn(enableAsyncMergeGlobalStats)
+
+	// concurrency of save stats to storage
+	analyzePartitionConcurrency, err := sctx.GetSessionVars().GlobalVarsAccessor.GetGlobalSysVar(variable.TiDBAnalyzePartitionConcurrency)
+	if err != nil {
+		return err
+	}
+	c, err := strconv.ParseInt(analyzePartitionConcurrency, 10, 64)
+	if err != nil {
+		return err
+	}
+	sctx.GetSessionVars().AnalyzePartitionConcurrency = int(c)
+
 	// analyzer version
 	verInString, err := sctx.GetSessionVars().GlobalVarsAccessor.GetGlobalSysVar(variable.TiDBAnalyzeVersion)
 	if err != nil {