table/index存储编码

RowKey

Rowkey形式如下

{tablePrefix}{tableID}{recordPrefixSep}{handle.Encode()}

prefix 常量值如下:

var (
	tablePrefix     = []byte{'t'}
	recordPrefixSep = []byte("_r")
	indexPrefixSep  = []byte("_i")
	metaPrefix      = []byte{'m'}
)

Handle

Handle is the ID of a row, 主要类型有：CommonHandle, IntHandle, PartitionHandle

CommonHandle 指非整形的handle 比如string等, IntHandle是int64的handle PartitionHandle 增加了一个PartitionID 字段

// Handle is the ID of a row.
type Handle interface {
	// IsInt returns if the handle type is int64.
	IsInt() bool
	// IntValue returns the int64 value if IsInt is true, it panics if IsInt returns false.
	IntValue() int64
	// Next returns the minimum handle that is greater than this handle.
	Next() Handle
	// Equal returns if the handle equals to another handle, it panics if the types are different.
	Equal(h Handle) bool
	// Compare returns the comparison result of the two handles, it panics if the types are different.
	Compare(h Handle) int
	// Encoded returns the encoded bytes.
	Encoded() []byte
	// Len returns the length of the encoded bytes.
	Len() int
	// NumCols returns the number of columns of the handle,
	NumCols() int
	// EncodedCol returns the encoded column value at the given column index.
	EncodedCol(idx int) []byte
	// Data returns the data of all columns of a handle.
	Data() ([]types.Datum, error)
	// String implements the fmt.Stringer interface.
	String() string
}

CommanHandle

// CommonHandle implements the Handle interface for non-int64 type handle.
type CommonHandle struct {
	encoded       []byte
	colEndOffsets []uint16
}

PartitionHandle

PartitionHandle 用于GlobalIndex

type PartitionHandle struct {
	Handle
	PartitionID int64
}

IntHandle

type IntHandle int64

Index

IndexKey

indexKey形式如下:

{tablePrefix}{phyTblID}{indexPrefixSep}{idxInfo.ID}{indexedValues}

一般的local index phyTblID用的是分区table对应的Physical table ID

Global Index

如果是GlobalIndex，phyTblID 则用的是tablInfo.ID, 真实的ParitionID会被编码到IndexKey的value中.

// GenIndexKey generates storage key for index values. Returned distinct indicates whether the
// indexed values should be distinct in storage (i.e. whether handle is encoded in the key).
func (c *index) GenIndexKey(sc *stmtctx.StatementContext, indexedValues []types.Datum, h kv.Handle, buf []byte) (key []byte, distinct bool, err error) {
	idxTblID := c.phyTblID
	if c.idxInfo.Global {
		idxTblID = c.tblInfo.ID
	}
	return tablecodec.GenIndexKey(sc, c.tblInfo, c.idxInfo, idxTblID, indexedValues, h, buf)
}

在PartitionHandlesToKVRanges中则会使用partitionID来计算handle的RowKey

Index Value Layout

DecodeIndexKV

IndexType

TiDB 中IndexType是为了兼容MySQL语法而设置的，在实际起到什么作用。

	IndexTypeBtree
	IndexTypeHash
	IndexTypeRtree

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