domon,statistics: remove useless code for sync load (#52358)

pkg/domain/domain.go

@@ -2243,11 +2243,10 @@ func quitStatsOwner(do *Domain, mgr owner.Manager) {
 // StartLoadStatsSubWorkers starts sub workers with new sessions to load stats concurrently.
 func (do *Domain) StartLoadStatsSubWorkers(ctxList []sessionctx.Context) {
 	statsHandle := do.StatsHandle()
-	for i, ctx := range ctxList {
+	for _, ctx := range ctxList {
 		// The sync load will affect how optimizer choose the plan.
 		// We need to assign high priority to it so that we can get the stats as quick as we can.
 		ctx.GetSessionVars().StmtCtx.Priority = mysql.HighPriority
-		statsHandle.SetSubCtxs(i, ctx)
 		do.wg.Add(1)
 		go statsHandle.SubLoadWorker(ctx, do.exit, do.wg)
 	}

pkg/statistics/handle/syncload/stats_syncload.go

@@ -45,7 +45,6 @@ type statsSyncLoad struct {
 func NewStatsSyncLoad(statsHandle statstypes.StatsHandle) statstypes.StatsSyncLoad {
 	s := &statsSyncLoad{statsHandle: statsHandle}
 	cfg := config.GetGlobalConfig()
-	s.StatsLoad.SubCtxs = make([]sessionctx.Context, cfg.Performance.StatsLoadConcurrency)
 	s.StatsLoad.NeededItemsCh = make(chan *statstypes.NeededItemTask, cfg.Performance.StatsLoadQueueSize)
 	s.StatsLoad.TimeoutItemsCh = make(chan *statstypes.NeededItemTask, cfg.Performance.StatsLoadQueueSize)
 	return s
@@ -58,12 +57,6 @@ type statsWrapper struct {
 	idx     *statistics.Index
 }
 
-// SetSubCtxs sets the sessionctx which is used to run queries background.
-// TODO: use SessionPool instead.
-func (s *statsSyncLoad) SetSubCtxs(idx int, sctx sessionctx.Context) {
-	s.StatsLoad.SubCtxs[idx] = sctx
-}
-
 // SendLoadRequests send neededColumns requests
 func (s *statsSyncLoad) SendLoadRequests(sc *stmtctx.StatementContext, neededHistItems []model.StatsLoadItem, timeout time.Duration) error {
 	remainedItems := s.removeHistLoadedColumns(neededHistItems)

pkg/statistics/handle/types/interfaces.go

@@ -398,7 +398,6 @@ type StatsLoad struct {
 	NeededItemsCh  chan *NeededItemTask
 	TimeoutItemsCh chan *NeededItemTask
 	Singleflight   singleflight.Group
-	SubCtxs        []sessionctx.Context
 	sync.Mutex
 }
 
@@ -418,10 +417,6 @@ type StatsSyncLoad interface {
 
 	// HandleOneTask will handle one task.
 	HandleOneTask(sctx sessionctx.Context, lastTask *NeededItemTask, exit chan struct{}) (task *NeededItemTask, err error)
-
-	// SetSubCtxs sets the sessionctx which is used to run queries background.
-	// TODO: use SessionPool instead.
-	SetSubCtxs(idx int, sctx sessionctx.Context)
 }
 
 // StatsGlobal is used to manage partition table global stats.