statistics: do not load unnecessary index statistics (#54060)

close #54022

pkg/statistics/handle/handle_hist.go

@@ -368,9 +368,9 @@ func (*Handle) readStatsForOneItem(sctx sessionctx.Context, item model.TableItem
 		return nil, errors.Trace(err)
 	}
 	if len(rows) == 0 {
-		logutil.BgLogger().Error("fail to get stats version for this histogram", zap.Int64("table_id", item.TableID),
+		logutil.BgLogger().Error("fail to get stats version for this histogram, normally this wouldn't happen, please check if this column or index has a histogram record in `mysql.stats_histogram`", zap.Int64("table_id", item.TableID),
 			zap.Int64("hist_id", item.ID), zap.Bool("is_index", item.IsIndex))
-		return nil, errors.Trace(fmt.Errorf("fail to get stats version for this histogram, table_id:%v, hist_id:%v, is_index:%v", item.TableID, item.ID, item.IsIndex))
+		return nil, errors.Trace(fmt.Errorf("fail to get stats version for this histogram, normally this wouldn't happen, please check if this column or index has a histogram record in `mysql.stats_histogram`, table_id:%v, hist_id:%v, is_index:%v", item.TableID, item.ID, item.IsIndex))
 	}
 	statsVer := rows[0].GetInt64(0)
 	if item.IsIndex {

pkg/statistics/handle/storage/read.go

@@ -540,8 +540,8 @@ func loadNeededColumnHistograms(sctx sessionctx.Context, statsCache util.StatsCa
 		return errors.Trace(err)
 	}
 	if len(rows) == 0 {
-		logutil.BgLogger().Error("fail to get stats version for this histogram", zap.Int64("table_id", col.TableID), zap.Int64("hist_id", col.ID))
-		return errors.Trace(fmt.Errorf("fail to get stats version for this histogram, table_id:%v, hist_id:%v", col.TableID, col.ID))
+		logutil.BgLogger().Error("fail to get stats version for this histogram, normally this wouldn't happen, please check if this column or index has a histogram record in `mysql.stats_histogram`", zap.Int64("table_id", col.TableID), zap.Int64("column_id", col.ID))
+		return errors.Trace(fmt.Errorf("fail to get stats version for this histogram, normally this wouldn't happen, please check if this column or index has a histogram record in `mysql.stats_histogram`, table_id:%v, column_id:%v", col.TableID, col.ID))
 	}
 	statsVer := rows[0].GetInt64(0)
 	colHist := &statistics.Column{
@@ -576,7 +576,16 @@ func loadNeededIndexHistograms(sctx sessionctx.Context, statsCache util.StatsCac
 		return nil
 	}
 	index, ok := tbl.Indices[idx.ID]
-	if !ok {
+	// Double check if the index is really needed to load.
+	// If we don't do this it might cause a memory leak.
+	// See: https://github.com/pingcap/tidb/issues/54022
+	if !ok || !index.IsLoadNeeded() {
+		if !index.IsLoadNeeded() {
+			logutil.BgLogger().Warn(
+				"Although the index stats is not required to load, an attempt is still made to load it, skip it",
+				zap.Int64("table_id", idx.TableID), zap.Int64("hist_id", idx.ID),
+			)
+		}
 		statistics.HistogramNeededItems.Delete(idx)
 		return nil
 	}
@@ -600,8 +609,8 @@ func loadNeededIndexHistograms(sctx sessionctx.Context, statsCache util.StatsCac
 		return errors.Trace(err)
 	}
 	if len(rows) == 0 {
-		logutil.BgLogger().Error("fail to get stats version for this histogram", zap.Int64("table_id", idx.TableID), zap.Int64("hist_id", idx.ID))
-		return errors.Trace(fmt.Errorf("fail to get stats version for this histogram, table_id:%v, hist_id:%v", idx.TableID, idx.ID))
+		logutil.BgLogger().Error("fail to get stats version for this histogram, normally this wouldn't happen, please check if this column or index has a histogram record in `mysql.stats_histogram`", zap.Int64("table_id", idx.TableID), zap.Int64("index_id", idx.ID))
+		return errors.Trace(fmt.Errorf("fail to get stats version for this histogram, normally this wouldn't happen, please check if this column or index has a histogram record in `mysql.stats_histogram`, table_id:%v, index_id:%v", idx.TableID, idx.ID))
 	}
 	idxHist := &statistics.Index{Histogram: *hg, CMSketch: cms, TopN: topN, FMSketch: fms,
 		Info: index.Info, StatsVer: rows[0].GetInt64(0),

tests/realtikvtest/statisticstest/BUILD.bazel

@@ -10,6 +10,8 @@ go_test(
     flaky = True,
     race = "on",
     deps = [
+        "//pkg/parser/model",
+        "//pkg/statistics",
         "//pkg/testkit",
         "//tests/realtikvtest",
         "@com_github_stretchr_testify//require",

tests/realtikvtest/statisticstest/statistics_test.go

@@ -15,9 +15,13 @@
 package statisticstest
 
 import (
+	"context"
 	"fmt"
 	"testing"
+	"time"
 
+	"github.com/pingcap/tidb/pkg/parser/model"
+	"github.com/pingcap/tidb/pkg/statistics"
 	"github.com/pingcap/tidb/pkg/testkit"
 	"github.com/pingcap/tidb/tests/realtikvtest"
 	"github.com/stretchr/testify/require"
@@ -232,3 +236,74 @@ func checkFMSketch(tk *testkit.TestKit) {
 	tk.MustQuery(`SHOW STATS_HISTOGRAMS WHERE TABLE_NAME='employees' and partition_name="global"  and column_name="id"`).CheckAt([]int{6}, [][]any{
 		{"14"}})
 }
+
+func TestNoNeedIndexStatsLoading(t *testing.T) {
+	store, dom := realtikvtest.CreateMockStoreAndDomainAndSetup(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test;")
+	tk.MustExec("drop table if exists t;")
+	// 1. Create a table and the statsHandle.Update(do.InfoSchema()) will load this table into the stats cache.
+	tk.MustExec("create table if not exists t(a int, b int, index ia(a));")
+	// 2. Drop the stats of the stats, it will clean up all system table records for this table.
+	tk.MustExec("drop stats t;")
+	// 3. Insert some data and wait for the modify_count and the count is not null in the mysql.stats_meta.
+	tk.MustExec("insert into t value(1,1), (2,2);")
+	h := dom.StatsHandle()
+	require.NoError(t, h.DumpStatsDeltaToKV(true))
+	require.Eventually(t, func() bool {
+		rows := tk.MustQuery("show stats_meta").Rows()
+		return len(rows) > 0
+	}, 1*time.Minute, 2*time.Millisecond)
+	require.NoError(t, h.Update(dom.InfoSchema()))
+	// 4. Try to select some data from this table by ID, it would trigger an async load.
+	tk.MustExec("set tidb_opt_objective='determinate';")
+	tk.MustQuery("select * from t where a = 1 and b = 1;").Check(testkit.Rows("1 1"))
+	table, err := dom.InfoSchema().TableByName(model.NewCIStr("test"), model.NewCIStr("t"))
+	require.NoError(t, err)
+	checkTableIDInItems(t, table.Meta().ID)
+}
+
+func checkTableIDInItems(t *testing.T, tableID int64) {
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Minute)
+	defer cancel()
+
+	ticker := time.NewTicker(2 * time.Millisecond)
+	defer ticker.Stop()
+
+	done := make(chan bool)
+
+	// First, confirm that the table ID is in the items.
+	items := statistics.HistogramNeededItems.AllItems()
+	for _, item := range items {
+		if item.TableID == tableID {
+			// Then, continuously check until it no longer exists or timeout.
+			go func() {
+				for {
+					select {
+					case <-ticker.C:
+						items := statistics.HistogramNeededItems.AllItems()
+						found := false
+						for _, item := range items {
+							if item.TableID == tableID {
+								found = true
+							}
+						}
+						if !found {
+							done <- true
+						}
+					case <-ctx.Done():
+						return
+					}
+				}
+			}()
+			break
+		}
+	}
+
+	select {
+	case <-done:
+		t.Log("Table ID has been removed from items")
+	case <-ctx.Done():
+		t.Fatal("Timeout: Table ID was not removed from items within the time limit")
+	}
+}