executor: fix data race in nullmap in hash join v2 (#57451)

ref #53127, close #57450

Author: windtalker

pkg/executor/join/join_table_meta.go

@@ -211,14 +211,12 @@ func newTableMeta(buildKeyIndex []int, buildTypes, buildKeyTypes, probeKeyTypes
 	keyIndexMap := make(map[int]struct{})
 	meta.serializeModes = make([]codec.SerializeMode, 0, len(buildKeyIndex))
 	isAllKeyInteger := true
-	hasFixedSizeKeyColumn := false
 	varLengthKeyNumber := 0
 	for index, keyIndex := range buildKeyIndex {
 		keyType := buildKeyTypes[index]
 		prop := getKeyProp(keyType)
 		if prop.keyLength != chunk.VarElemLen {
 			meta.joinKeysLength += prop.keyLength
-			hasFixedSizeKeyColumn = true
 		} else {
 			meta.isJoinKeysFixedLength = false
 			varLengthKeyNumber++
@@ -327,20 +325,10 @@ func newTableMeta(buildKeyIndex []int, buildTypes, buildKeyTypes, probeKeyTypes
 	}
 	if needUsedFlag {
 		meta.colOffsetInNullMap = 1
-		// the total row length should be larger than 4 byte since the smallest unit of atomic.LoadXXX is UInt32
-		if len(columnsNeedToBeSaved) > 0 {
-			// the smallest length of a column is 4 byte, so the total row length is enough
-			meta.nullMapLength = (len(columnsNeedToBeSaved) + 1 + 7) / 8
-		} else {
-			// if no columns need to be converted to row format, then the key is not inlined
-			// 1. if any of the key columns is fixed length, then the row length is larger than 4 bytes(since the smallest length of a fixed length column is 4 bytes)
-			// 2. if all the key columns are variable length, there is no guarantee that the row length is larger than 4 byte, the nullmap should be 4 bytes alignment
-			if hasFixedSizeKeyColumn {
-				meta.nullMapLength = (len(columnsNeedToBeSaved) + 1 + 7) / 8
-			} else {
-				meta.nullMapLength = ((len(columnsNeedToBeSaved) + 1 + 31) / 32) * 4
-			}
-		}
+		// If needUsedFlag == true, during probe stage, the usedFlag will be accessed by both read/write operator,
+		// so atomic read/write is required. We want to keep this atomic operator inside the access of nullmap,
+		// then the nullMapLength should be 4 bytes alignment since the smallest unit of atomic.LoadUint32 is UInt32
+		meta.nullMapLength = ((len(columnsNeedToBeSaved) + 1 + 31) / 32) * 4
 	} else {
 		meta.colOffsetInNullMap = 0
 		meta.nullMapLength = (len(columnsNeedToBeSaved) + 7) / 8

pkg/executor/join/join_table_meta_test.go

@@ -297,14 +297,12 @@ func TestJoinTableMetaNullMapLength(t *testing.T) {
 		// nullmap only used for columns that needed to be converted to rows
 		{[]int{0}, []*types.FieldType{stringTp}, []*types.FieldType{stringTp}, []*types.FieldType{stringTp}, []int{}, false, 0},
 		{[]int{0}, []*types.FieldType{stringTp, intTp, intTp, intTp}, []*types.FieldType{stringTp}, []*types.FieldType{stringTp}, []int{}, false, 0},
-		// usedFlag is true
-		// the row length is at least 4 bytes, so nullmap is 1 byte alignment
-		{[]int{0}, []*types.FieldType{intTp}, []*types.FieldType{intTp}, []*types.FieldType{intTp}, nil, true, 1},
-		{[]int{0}, []*types.FieldType{stringTp, intTp}, []*types.FieldType{stringTp}, []*types.FieldType{stringTp}, []int{1}, true, 1},
-		{[]int{0}, []*types.FieldType{stringTp, intTp}, []*types.FieldType{stringTp}, []*types.FieldType{stringTp}, []int{0}, true, 1},
-		{[]int{0, 1}, []*types.FieldType{stringTp, intTp}, []*types.FieldType{stringTp, intTp}, []*types.FieldType{stringTp, intTp}, []int{}, true, 1},
-		{[]int{0}, []*types.FieldType{intTp}, []*types.FieldType{intTp}, []*types.FieldType{uintTp}, []int{}, true, 1},
-		// the row length is not guaranteed to be at least 4 bytes, nullmap is 4 bytes alignment
+		// usedFlag is true, nullmap is 4 byte alignment
+		{[]int{0}, []*types.FieldType{intTp}, []*types.FieldType{intTp}, []*types.FieldType{intTp}, nil, true, 4},
+		{[]int{0}, []*types.FieldType{stringTp, intTp}, []*types.FieldType{stringTp}, []*types.FieldType{stringTp}, []int{1}, true, 4},
+		{[]int{0}, []*types.FieldType{stringTp, intTp}, []*types.FieldType{stringTp}, []*types.FieldType{stringTp}, []int{0}, true, 4},
+		{[]int{0, 1}, []*types.FieldType{stringTp, intTp}, []*types.FieldType{stringTp, intTp}, []*types.FieldType{stringTp, intTp}, []int{}, true, 4},
+		{[]int{0}, []*types.FieldType{intTp}, []*types.FieldType{intTp}, []*types.FieldType{uintTp}, []int{}, true, 4},
 		{[]int{0}, []*types.FieldType{stringTp}, []*types.FieldType{stringTp}, []*types.FieldType{stringTp}, []int{}, true, 4},
 		{[]int{0, 1}, []*types.FieldType{stringTp, stringTp}, []*types.FieldType{stringTp, stringTp}, []*types.FieldType{stringTp, stringTp}, []int{}, true, 4},
 	}