*: remove useless cache in the MergePartitionStats2GlobalStats (#47217)

ref #47219

statistics/handle/globalstats/global_stats.go

@@ -84,7 +84,6 @@ func MergePartitionStats2GlobalStats(
 	loadTablePartitionStatsFn loadTablePartitionStatsFunc,
 ) (globalStats *GlobalStats, err error) {
 	partitionNum := len(globalTableInfo.Partition.Definitions)
-	allPartitionStats := make(map[int64]*statistics.Table)
 	if len(histIDs) == 0 {
 		for _, col := range globalTableInfo.Columns {
 			// The virtual generated column stats can not be merged to the global stats.
@@ -122,27 +121,21 @@ func MergePartitionStats2GlobalStats(
 			err = errors.Errorf("unknown physical ID %d in stats meta table, maybe it has been dropped", partitionID)
 			return
 		}
-
 		tableInfo := partitionTable.Meta()
 		var partitionStats *statistics.Table
-
-		partitionStats, ok = allPartitionStats[partitionID]
-		// If pre-load partition stats isn't provided, then we load partition stats directly and set it into allPartitionStats
-		if !ok {
-			var err1 error
-			partitionStats, err1 = loadTablePartitionStatsFn(tableInfo, &def)
-			if err1 != nil {
-				if skipMissingPartitionStats && types.ErrPartitionStatsMissing.Equal(err) {
-					globalStats.MissingPartitionStats = append(globalStats.MissingPartitionStats, fmt.Sprintf("partition `%s`", def.Name.L))
-					continue
-				}
-				err = err1
-				return
+		partitionStats, err1 := loadTablePartitionStatsFn(tableInfo, &def)
+		if err1 != nil {
+			if skipMissingPartitionStats && types.ErrPartitionStatsMissing.Equal(err) {
+				globalStats.MissingPartitionStats = append(globalStats.MissingPartitionStats, fmt.Sprintf("partition `%s`", def.Name.L))
+				continue
 			}
-			allPartitionStats[partitionID] = partitionStats
+			err = err1
+			return
 		}
 
 		for i := 0; i < globalStats.Num; i++ {
+			// GetStatsInfo will return the copy of the statsInfo, so we don't need to worry about the data race.
+			// partitionStats will be released after the for loop.
 			hg, cms, topN, fms, analyzed := partitionStats.GetStatsInfo(histIDs[i], isIndex)
 			skipPartition := false
 			if !analyzed {
@@ -189,6 +182,7 @@ func MergePartitionStats2GlobalStats(
 				allFms[i] = append(allFms[i], fms)
 			}
 		}
+		partitionStats.ReleaseAndPutToPool()
 	}
 
 	// After collect all the statistics from the partition-level stats,
@@ -249,9 +243,6 @@ func MergePartitionStats2GlobalStats(
 
 		globalStats.Hg[i].NDV = globalStatsNDV
 	}
-	for _, value := range allPartitionStats {
-		value.ReleaseAndPutToPool()
-	}
 	return
 }