TiDB 基本数据类型

Datum

// Datum is a data box holds different kind of data.
// It has better performance and is easier to use than `interface{}`.
type Datum struct {
	k         byte        // datum kind.
	decimal   uint16      // decimal can hold uint16 values.
	length    uint32      // length can hold uint32 values.
	i         int64       // i can hold int64 uint64 float64 values.
	collation string      // collation hold the collation information for string value.
	b         []byte      // b can hold string or []byte values.
	x         interface{} // x hold all other types.
}

const (
	KindNull          byte = 0
	KindInt64         byte = 1
	KindUint64        byte = 2
	KindFloat32       byte = 3
	KindFloat64       byte = 4
	KindString        byte = 5
	KindBytes         byte = 6
	KindBinaryLiteral byte = 7 // Used for BIT / HEX literals.
	KindMysqlDecimal  byte = 8
	KindMysqlDuration byte = 9
	KindMysqlEnum     byte = 10
	KindMysqlBit      byte = 11 // Used for BIT table column values.
	KindMysqlSet      byte = 12
	KindMysqlTime     byte = 13
	KindInterface     byte = 14
	KindMinNotNull    byte = 15
	KindMaxValue      byte = 16
	KindRaw           byte = 17
	KindMysqlJSON     byte = 18
)

Chunk

// Chunk stores multiple rows of data in Apache Arrow format.
// See https://arrow.apache.org/docs/format/Columnar.html#physical-memory-layout
// Values are appended in compact format and can be directly accessed without decoding.
// When the chunk is done processing, we can reuse the allocated memory by resetting it.
type Chunk struct {
	// sel indicates which rows are selected.
	// If it is nil, all rows are selected.
	sel []int

	columns []*Column
	// numVirtualRows indicates the number of virtual rows, which have zero Column.
	// It is used only when this Chunk doesn't hold any data, i.e. "len(columns)==0".
	numVirtualRows int
	// capacity indicates the max number of rows this chunk can hold.
	// TODO: replace all usages of capacity to requiredRows and remove this field
	capacity int

	// requiredRows indicates how many rows the parent executor want.
	requiredRows int
}

Column

Column offsets[i]表示第i个元素在data中的偏移, data和elmBuf分别作用是啥？ elmBuf用来临时append value,将value转为[]byte，然后再append到data上 fixed sized的offsfet数组就不用了，可以直接算出来，这样就省下了offset这个数组.

// Column stores one column of data in Apache Arrow format.
// See https://arrow.apache.org/docs/memory_layout.html
type Column struct {
	length     int
	nullBitmap []byte // bit 0 is null, 1 is not null
	offsets    []int64
	data       []byte
	elemBuf    []byte
}

Row

// Row represents a row of data, can be used to access values.
type Row struct {
	c   *Chunk
	idx int
}

Range

// Range represents a range generated in physical plan building phase.
type Range struct {
	LowVal  []types.Datum
	HighVal []types.Datum

	LowExclude  bool // Low value is exclusive.
	HighExclude bool // High value is exclusive.
}

RowContainer

// RowContainer provides a place for many rows, so many that we might want to spill them into disk.
type RowContainer struct {
	m struct {
		// RWMutex guarantees spill and get operator for rowContainer is mutually exclusive.
		sync.RWMutex
		// records stores the chunks in memory.
		records *List
		// recordsInDisk stores the chunks in disk.
		recordsInDisk *ListInDisk
		// spillError stores the error when spilling.
		spillError error
	}

	fieldType []*types.FieldType
	chunkSize int
	numRow    int

	memTracker  *memory.Tracker
	diskTracker *disk.Tracker
	actionSpill *SpillDiskAction
}