use uint32 to split string column

go/vt/tabletserver/query_splitter.go

@@ -309,20 +309,15 @@ func (qs *QuerySplitter) splitBoundariesFloatColumn(pkMinMax *mproto.QueryResult
 
 // TODO(shengzhe): support split based on min, max from the string column.
 func (qs *QuerySplitter) splitBoundariesStringColumn() ([]sqltypes.Value, error) {
-	firstRow := int64(0x0)
-	lastRow := int64(0xFFFFFFFFFFFFFF)
-	splitRange := lastRow - firstRow + 1
+	splitRange := int64(0xFFFFFFFF) + 1
 	splitSize := splitRange / int64(qs.splitCount)
-	qs.rowCount = splitSize
+	//TODO(shengzhe): have a better estimated row count based on table size.
+	qs.rowCount = int64(splitSize)
 	var boundaries []sqltypes.Value
 	for i := 1; i < qs.splitCount; i++ {
-		buf := make([]byte, 8)
-		// encode split point into binaries.
-		binary.BigEndian.PutUint64(buf, uint64(firstRow+splitSize*int64(i)))
-		// only converts the lower 4 bytes into hex because the upper 4 bytes are
-		// always 0x00000000 and mysql does byte comparison from the most significant
-		// bits.
-		val, err := sqltypes.BuildValue(buf[4:])
+		buf := make([]byte, 4)
+		binary.BigEndian.PutUint32(buf, uint32(splitSize)*uint32(i))
+		val, err := sqltypes.BuildValue(buf)
 		if err != nil {
 			return nil, err
 		}

go/vt/tabletserver/query_splitter_test.go

@@ -444,26 +444,23 @@ func TestSplitQueryStringColumn(t *testing.T) {
 	}
 	got := []proto.BoundQuery{}
 	for _, split := range splits {
-		if split.RowCount != 24019198012642645 {
-			t.Errorf("wrong RowCount, got: %v, want: %v", split.RowCount, 1431655765)
-		}
 		got = append(got, split.Query)
 	}
 	want := []proto.BoundQuery{
 		{
 			Sql:           "select * from test_table where (count > :count) and (id < :" + endBindVarName + ")",
-			BindVariables: map[string]interface{}{endBindVarName: hexToByteUInt64(0x55555555)[4:]},
+			BindVariables: map[string]interface{}{endBindVarName: hexToByteUInt32(0x55555555)},
 		},
 		{
 			Sql: fmt.Sprintf("select * from test_table where (count > :count) and (id >= :%s and id < :%s)", startBindVarName, endBindVarName),
 			BindVariables: map[string]interface{}{
-				startBindVarName: hexToByteUInt64(0x55555555)[4:],
-				endBindVarName:   hexToByteUInt64(0xAAAAAAAA)[4:],
+				startBindVarName: hexToByteUInt32(0x55555555),
+				endBindVarName:   hexToByteUInt32(0xAAAAAAAA),
 			},
 		},
 		{
 			Sql:           "select * from test_table where (count > :count) and (id >= :" + startBindVarName + ")",
-			BindVariables: map[string]interface{}{startBindVarName: hexToByteUInt64(0xAAAAAAAA)[4:]},
+			BindVariables: map[string]interface{}{startBindVarName: hexToByteUInt32(0xAAAAAAAA)},
 		},
 	}
 	if !reflect.DeepEqual(got, want) {
@@ -471,8 +468,8 @@ func TestSplitQueryStringColumn(t *testing.T) {
 	}
 }
 
-func hexToByteUInt64(val uint64) []byte {
-	buf := make([]byte, 8)
-	binary.BigEndian.PutUint64(buf, val)
+func hexToByteUInt32(val uint32) []byte {
+	buf := make([]byte, 4)
+	binary.BigEndian.PutUint32(buf, val)
 	return buf
 }