*: show cmd to check if all needed histograms are loaded (#29672)

executor/show.go

@@ -196,6 +196,9 @@ func (e *ShowExec) fetchAll(ctx context.Context) error {
 	case ast.ShowStatsHealthy:
 		e.fetchShowStatsHealthy()
 		return nil
+	case ast.ShowHistogramsInFlight:
+		e.fetchShowHistogramsInFlight()
+		return nil
 	case ast.ShowColumnStatsUsage:
 		return e.fetchShowColumnStatsUsage()
 	case ast.ShowPlugins:

executor/show_stats.go

@@ -443,6 +443,10 @@ func (e *ShowExec) appendTableForStatsHealthy(dbName, tblName, partitionName str
 	})
 }
 
+func (e *ShowExec) fetchShowHistogramsInFlight() {
+	e.appendRow([]interface{}{statistics.HistogramNeededColumns.Length()})
+}
+
 func (e *ShowExec) fetchShowAnalyzeStatus() {
 	rows := dataForAnalyzeStatusHelper(e.baseExecutor.ctx)
 	for _, row := range rows {

executor/show_stats_test.go

@@ -350,3 +350,16 @@ func TestShowColumnStatsUsage(t *testing.T) {
 	require.Equal(t, rows[0], []interface{}{"test", "t2", "global", t1.Meta().Columns[0].Name.O, "2021-10-20 09:00:00", "<nil>"})
 	require.Equal(t, rows[1], []interface{}{"test", "t2", p0.Name.O, t1.Meta().Columns[0].Name.O, "2021-10-20 09:00:00", "<nil>"})
 }
+
+func TestShowHistogramsInFlight(t *testing.T) {
+	t.Parallel()
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	result := tk.MustQuery("show histograms_in_flight")
+	rows := result.Rows()
+	require.Equal(t, len(rows), 1)
+	require.Equal(t, rows[0][0], "0")
+}

parser/ast/dml.go

@@ -2580,6 +2580,7 @@ const (
 	ShowStatsTopN
 	ShowStatsBuckets
 	ShowStatsHealthy
+	ShowHistogramsInFlight
 	ShowColumnStatsUsage
 	ShowPlugins
 	ShowProfile
@@ -2768,6 +2769,11 @@ func (n *ShowStmt) Restore(ctx *format.RestoreCtx) error {
 		if err := restoreShowLikeOrWhereOpt(); err != nil {
 			return err
 		}
+	case ShowHistogramsInFlight:
+		ctx.WriteKeyWord("HISTOGRAMS_IN_FLIGHT")
+		if err := restoreShowLikeOrWhereOpt(); err != nil {
+			return err
+		}
 	case ShowColumnStatsUsage:
 		ctx.WriteKeyWord("COLUMN_STATS_USAGE")
 		if err := restoreShowLikeOrWhereOpt(); err != nil {

parser/misc.go

@@ -670,6 +670,7 @@ var tokenMap = map[string]int{
 	"STATS_HISTOGRAMS":         statsHistograms,
 	"STATS_TOPN":               statsTopN,
 	"STATS_META":               statsMeta,
+	"HISTOGRAMS_IN_FLIGHT":     histogramsInFlight,
 	"STATS_PERSISTENT":         statsPersistent,
 	"STATS_SAMPLE_PAGES":       statsSamplePages,
 	"STATS":                    stats,

parser/parser.y

@@ -736,6 +736,7 @@ import (
 	statsBuckets               "STATS_BUCKETS"
 	statsHealthy               "STATS_HEALTHY"
 	statsTopN                  "STATS_TOPN"
+	histogramsInFlight         "HISTOGRAMS_IN_FLIGHT"
 	telemetry                  "TELEMETRY"
 	telemetryID                "TELEMETRY_ID"
 	tidb                       "TIDB"
@@ -6079,6 +6080,7 @@ TiDBKeyword:
 |	"STATS_TOPN"
 |	"STATS_BUCKETS"
 |	"STATS_HEALTHY"
+|	"HISTOGRAMS_IN_FLIGHT"
 |	"TELEMETRY"
 |	"TELEMETRY_ID"
 |	"TIDB"
@@ -10665,6 +10667,10 @@ ShowTargetFilterable:
 	{
 		$$ = &ast.ShowStmt{Tp: ast.ShowStatsHealthy}
 	}
+|	"HISTOGRAMS_IN_FLIGHT"
+	{
+		$$ = &ast.ShowStmt{Tp: ast.ShowHistogramsInFlight}
+	}
 |	"COLUMN_STATS_USAGE"
 	{
 		$$ = &ast.ShowStmt{Tp: ast.ShowColumnStatsUsage}

parser/parser_test.go

@@ -1128,6 +1128,8 @@ func TestDBAStmt(t *testing.T) {
 		// for show stats_topn.
 		{"show stats_topn", true, "SHOW STATS_TOPN"},
 		{"show stats_topn where table_name = 't'", true, "SHOW STATS_TOPN WHERE `table_name`=_UTF8MB4't'"},
+		// for show histograms_in_flight.
+		{"show histograms_in_flight", true, "SHOW HISTOGRAMS_IN_FLIGHT"},
 		// for show column_stats_usage.
 		{"show column_stats_usage", true, "SHOW COLUMN_STATS_USAGE"},
 		{"show column_stats_usage where table_name = 't'", true, "SHOW COLUMN_STATS_USAGE WHERE `table_name`=_UTF8MB4't'"},

planner/core/planbuilder.go

@@ -2589,7 +2589,7 @@ func (b *PlanBuilder) buildShow(ctx context.Context, show *ast.ShowStmt) (Plan,
 		p.setSchemaAndNames(buildShowNextRowID())
 		b.visitInfo = appendVisitInfo(b.visitInfo, mysql.SelectPriv, show.Table.Schema.L, show.Table.Name.L, "", ErrPrivilegeCheckFail)
 		return p, nil
-	case ast.ShowStatsBuckets, ast.ShowStatsHistograms, ast.ShowStatsMeta, ast.ShowStatsExtended, ast.ShowStatsHealthy, ast.ShowStatsTopN, ast.ShowColumnStatsUsage:
+	case ast.ShowStatsBuckets, ast.ShowStatsHistograms, ast.ShowStatsMeta, ast.ShowStatsExtended, ast.ShowStatsHealthy, ast.ShowStatsTopN, ast.ShowHistogramsInFlight, ast.ShowColumnStatsUsage:
 		user := b.ctx.GetSessionVars().User
 		var err error
 		if user != nil {
@@ -4352,6 +4352,9 @@ func buildShowSchema(s *ast.ShowStmt, isView bool, isSequence bool) (schema *exp
 	case ast.ShowStatsHealthy:
 		names = []string{"Db_name", "Table_name", "Partition_name", "Healthy"}
 		ftypes = []byte{mysql.TypeVarchar, mysql.TypeVarchar, mysql.TypeVarchar, mysql.TypeLonglong}
+	case ast.ShowHistogramsInFlight:
+		names = []string{"HistogramsInFlight"}
+		ftypes = []byte{mysql.TypeLonglong}
 	case ast.ShowColumnStatsUsage:
 		names = []string{"Db_name", "Table_name", "Partition_name", "Column_name", "Last_used_at", "Last_analyzed_at"}
 		ftypes = []byte{mysql.TypeVarchar, mysql.TypeVarchar, mysql.TypeVarchar, mysql.TypeVarchar, mysql.TypeDatetime, mysql.TypeDatetime}

statistics/table.go

@@ -236,17 +236,17 @@ type tableColumnID struct {
 }
 
 type neededColumnMap struct {
-	m    sync.Mutex
+	m    sync.RWMutex
 	cols map[tableColumnID]struct{}
 }
 
 func (n *neededColumnMap) AllCols() []tableColumnID {
-	n.m.Lock()
+	n.m.RLock()
 	keys := make([]tableColumnID, 0, len(n.cols))
 	for key := range n.cols {
 		keys = append(keys, key)
 	}
-	n.m.Unlock()
+	n.m.RUnlock()
 	return keys
 }
 
@@ -262,6 +262,12 @@ func (n *neededColumnMap) Delete(col tableColumnID) {
 	n.m.Unlock()
 }
 
+func (n *neededColumnMap) Length() int {
+	n.m.RLock()
+	defer n.m.RUnlock()
+	return len(n.cols)
+}
+
 // RatioOfPseudoEstimate means if modifyCount / statsTblCount is greater than this ratio, we think the stats is invalid
 // and use pseudo estimation.
 var RatioOfPseudoEstimate = atomic.NewFloat64(0.7)