stats: fix panic caused by outdated feedback (#7128)

statistics/update.go

@@ -29,6 +29,7 @@ import (
 	"github.com/pingcap/tidb/sessionctx"
 	"github.com/pingcap/tidb/sessionctx/variable"
 	"github.com/pingcap/tidb/store/tikv/oracle"
+	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/util/sqlexec"
 	log "github.com/sirupsen/logrus"
 	"golang.org/x/net/context"
@@ -284,80 +285,90 @@ func (h *Handle) HandleUpdateStats(is infoschema.InfoSchema) error {
 	if len(rows) == 0 || err != nil {
 		return errors.Trace(err)
 	}
-	tableID, histID, isIndex := int64(-1), int64(-1), int64(-1)
-	q := &QueryFeedback{}
-	var (
-		cms  *CMSketch
-		hist *Histogram
-	)
-	for _, row := range rows {
-		// merge into previous feedback
-		if row.GetInt64(0) == tableID && row.GetInt64(1) == histID && row.GetInt64(2) == isIndex {
-			err = decodeFeedback(row.GetBytes(3), q, cms)
-			if err != nil {
-				log.Debugf("decode feedback failed, err: %v", errors.ErrorStack(err))
-			}
-			continue
+
+	var groupedRows [][]types.Row
+	preIdx := 0
+	tableID, histID, isIndex := rows[0].GetInt64(0), rows[0].GetInt64(1), rows[0].GetInt64(2)
+	for i := 1; i < len(rows); i++ {
+		row := rows[i]
+		if row.GetInt64(0) != tableID || row.GetInt64(1) != histID || row.GetInt64(2) != isIndex {
+			groupedRows = append(groupedRows, rows[preIdx:i])
+			tableID, histID, isIndex = row.GetInt64(0), row.GetInt64(1), row.GetInt64(2)
+			preIdx = i
 		}
-		// dump the stats into kv
-		if hist != nil {
-			err = h.dumpStatsUpdateToKV(tableID, int(isIndex), q, hist, cms)
-			if err != nil {
-				return errors.Trace(err)
-			}
+	}
+	groupedRows = append(groupedRows, rows[preIdx:])
+
+	for _, rows := range groupedRows {
+		if err := h.handleSingleHistogramUpdate(is, rows); err != nil {
+			return errors.Trace(err)
 		}
-		// initialize new feedback
-		tableID, histID, isIndex = row.GetInt64(0), row.GetInt64(1), row.GetInt64(2)
-		table, ok := is.TableByID(tableID)
-		if !ok {
-			hist, cms = nil, nil
-			continue
+	}
+	return nil
+}
+
+// handleSingleHistogramUpdate updates the Histogram and CM Sketch using these feedbacks. All the feedbacks for
+// the same index or column are gathered in `rows`.
+func (h *Handle) handleSingleHistogramUpdate(is infoschema.InfoSchema, rows []types.Row) (err error) {
+	tableID, histID, isIndex := rows[0].GetInt64(0), rows[0].GetInt64(1), rows[0].GetInt64(2)
+	defer func() {
+		if err == nil {
+			err = errors.Trace(h.deleteOutdatedFeedback(tableID, histID, isIndex))
 		}
-		tbl := h.GetTableStats(table.Meta())
-		if isIndex == 1 {
-			idx, ok := tbl.Indices[histID]
-			if !ok {
-				hist, cms = nil, nil
-				continue
-			}
-			hist = &idx.Histogram
+	}()
+	table, ok := is.TableByID(tableID)
+	// The table has been deleted.
+	if !ok {
+		return nil
+	}
+	tbl := h.GetTableStats(table.Meta())
+	var cms *CMSketch
+	var hist *Histogram
+	if isIndex == 1 {
+		idx, ok := tbl.Indices[histID]
+		if ok {
+			idxHist := idx.Histogram
+			hist = &idxHist
 			cms = idx.CMSketch.copy()
-		} else {
-			col, ok := tbl.Columns[histID]
-			if !ok {
-				hist, cms = nil, nil
-				continue
-			}
-			hist = &col.Histogram
-			cms = nil
 		}
-		err = decodeFeedback(row.GetBytes(3), q, cms)
-		if err != nil {
+	} else {
+		col, ok := tbl.Columns[histID]
+		if ok {
+			colHist := col.Histogram
+			hist = &colHist
+		}
+	}
+	// The column or index has been deleted.
+	if hist == nil {
+		return nil
+	}
+	q := &QueryFeedback{}
+	for _, row := range rows {
+		err1 := decodeFeedback(row.GetBytes(3), q, cms)
+		if err1 != nil {
 			log.Debugf("decode feedback failed, err: %v", errors.ErrorStack(err))
 		}
 	}
-	// dump the last feedback into kv
-	err = h.dumpStatsUpdateToKV(tableID, int(isIndex), q, hist, cms)
+	// Update the NDV of primary key column.
+	if table.Meta().PKIsHandle && isIndex == 0 {
+		hist.NDV = int64(hist.totalRowCount())
+	}
+	err = h.dumpStatsUpdateToKV(tableID, isIndex, q, hist, cms)
 	return errors.Trace(err)
 }
 
-func (h *Handle) dumpStatsUpdateToKV(tableID int64, isIndex int, q *QueryFeedback, hist *Histogram, cms *CMSketch) (err error) {
-	defer func() {
-		if err != nil {
-			metrics.UpdateStatsCounter.WithLabelValues(metrics.LblError).Inc()
-		} else {
-			metrics.UpdateStatsCounter.WithLabelValues(metrics.LblOK).Inc()
-		}
-	}()
-	hist = UpdateHistogram(hist, q)
-	err = SaveStatsToStorage(h.ctx, tableID, -1, isIndex, hist, cms)
-	if err != nil {
-		return errors.Trace(err)
-	}
+func (h *Handle) deleteOutdatedFeedback(tableID, histID, isIndex int64) error {
 	h.ctx.GetSessionVars().BatchDelete = true
-	sql := fmt.Sprintf("delete from mysql.stats_feedback where table_id = %d and hist_id = %d and is_index = %d", tableID, hist.ID, isIndex)
-	_, err = h.ctx.(sqlexec.SQLExecutor).Execute(context.TODO(), sql)
-	q.feedback = q.feedback[:0]
+	sql := fmt.Sprintf("delete from mysql.stats_feedback where table_id = %d and hist_id = %d and is_index = %d", tableID, histID, isIndex)
+	_, err := h.ctx.(sqlexec.SQLExecutor).Execute(context.TODO(), sql)
+	h.ctx.GetSessionVars().BatchDelete = false
+	return errors.Trace(err)
+}
+
+func (h *Handle) dumpStatsUpdateToKV(tableID, isIndex int64, q *QueryFeedback, hist *Histogram, cms *CMSketch) error {
+	hist = UpdateHistogram(hist, q)
+	err := SaveStatsToStorage(h.ctx, tableID, -1, int(isIndex), hist, cms)
+	metrics.UpdateStatsCounter.WithLabelValues(metrics.RetLabel(err)).Inc()
 	return errors.Trace(err)
 }
 

statistics/update_test.go

@@ -542,6 +542,16 @@ func (s *testStatsUpdateSuite) TestQueryFeedback(c *C) {
 		feedback := h.GetQueryFeedback()
 		c.Assert(len(feedback), Equals, 0)
 	}
+
+	// Test that the outdated feedback won't cause panic.
+	statistics.FeedbackProbability = 1
+	for _, t := range tests {
+		testKit.MustQuery(t.sql)
+	}
+	c.Assert(h.DumpStatsDeltaToKV(), IsNil)
+	c.Assert(h.DumpStatsFeedbackToKV(), IsNil)
+	testKit.MustExec("drop table t")
+	c.Assert(h.HandleUpdateStats(s.do.InfoSchema()), IsNil)
 }
 
 func (s *testStatsUpdateSuite) TestUpdateSystemTable(c *C) {