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chunk.go
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// Copyright 2017 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package chunk
import (
"encoding/binary"
"unsafe"
"github.com/cznic/mathutil"
"github.com/pingcap/tidb/types"
"github.com/pingcap/tidb/types/json"
)
// Chunk stores multiple rows of data in Apache Arrow format.
// See https://arrow.apache.org/docs/memory_layout.html
// 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 {
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.
capacity int
}
// Capacity constants.
const (
InitialCapacity = 32
ZeroCapacity = 0
)
// NewChunkWithCapacity creates a new chunk with field types and capacity.
func NewChunkWithCapacity(fields []*types.FieldType, cap int) *Chunk {
return New(fields, cap, cap) //FIXME: in following PR.
}
// New creates a new chunk.
// cap: the limit for the max number of rows.
// maxChunkSize: the max limit for the number of rows.
func New(fields []*types.FieldType, cap, maxChunkSize int) *Chunk {
chk := new(Chunk)
chk.columns = make([]*column, 0, len(fields))
chk.capacity = mathutil.Min(cap, maxChunkSize)
for _, f := range fields {
elemLen := getFixedLen(f)
if elemLen == varElemLen {
chk.columns = append(chk.columns, newVarLenColumn(chk.capacity, nil))
} else {
chk.columns = append(chk.columns, newFixedLenColumn(elemLen, chk.capacity))
}
}
chk.numVirtualRows = 0
return chk
}
// Renew creates a new Chunk based on an existing Chunk. The newly created Chunk
// has the same data schema with the old Chunk. The capacity of the new Chunk
// might be doubled based on the capacity of the old Chunk and the maxChunkSize.
// chk: old chunk(often used in previous call).
// maxChunkSize: the limit for the max number of rows.
func Renew(chk *Chunk, maxChunkSize int) *Chunk {
newChk := new(Chunk)
if chk.columns == nil {
return newChk
}
newCap := reCalcCapacity(chk, maxChunkSize)
newChk.columns = renewColumns(chk.columns, newCap)
newChk.numVirtualRows = 0
newChk.capacity = newCap
return newChk
}
// renewColumns creates the columns of a Chunk. The capacity of the newly
// created columns is equal to cap.
func renewColumns(oldCol []*column, cap int) []*column {
columns := make([]*column, 0, len(oldCol))
for _, col := range oldCol {
if col.isFixed() {
columns = append(columns, newFixedLenColumn(len(col.elemBuf), cap))
} else {
columns = append(columns, newVarLenColumn(cap, col))
}
}
return columns
}
// MemoryUsage returns the total memory usage of a Chunk in B.
// We ignore the size of column.length and column.nullCount
// since they have little effect of the total memory usage.
func (c *Chunk) MemoryUsage() (sum int64) {
for _, col := range c.columns {
curColMemUsage := int64(unsafe.Sizeof(*col)) + int64(cap(col.nullBitmap)) + int64(cap(col.offsets)*4) + int64(cap(col.data)) + int64(cap(col.elemBuf))
sum += curColMemUsage
}
return
}
// newFixedLenColumn creates a fixed length column with elemLen and initial data capacity.
func newFixedLenColumn(elemLen, cap int) *column {
return &column{
elemBuf: make([]byte, elemLen),
data: make([]byte, 0, cap*elemLen),
nullBitmap: make([]byte, 0, cap>>3),
}
}
// newVarLenColumn creates a variable length column with initial data capacity.
func newVarLenColumn(cap int, old *column) *column {
estimatedElemLen := 8
// For varLenColumn (e.g. varchar), the accurate length of an element is unknown.
// Therefore, in the first executor.Next we use an experience value -- 8 (so it may make runtime.growslice)
// but in the following Next call we estimate the length as AVG x 1.125 elemLen of the previous call.
if old != nil && old.length != 0 {
estimatedElemLen = (len(old.data) + len(old.data)/8) / old.length
}
return &column{
offsets: make([]int32, 1, cap+1),
data: make([]byte, 0, cap*estimatedElemLen),
nullBitmap: make([]byte, 0, cap>>3),
}
}
// MakeRef makes column in "dstColIdx" reference to column in "srcColIdx".
func (c *Chunk) MakeRef(srcColIdx, dstColIdx int) {
c.columns[dstColIdx] = c.columns[srcColIdx]
}
// SwapColumn swaps column "c.columns[colIdx]" with column
// "other.columns[otherIdx]". If there exists columns refer to the column to be
// swapped, we need to re-build the reference.
func (c *Chunk) SwapColumn(colIdx int, other *Chunk, otherIdx int) {
// Find the leftmost column of the reference which is the actual column to
// be swapped.
for i := 0; i < colIdx; i++ {
if c.columns[i] == c.columns[colIdx] {
colIdx = i
}
}
for i := 0; i < otherIdx; i++ {
if other.columns[i] == other.columns[otherIdx] {
otherIdx = i
}
}
// Find the columns which refer to the actual column to be swapped.
refColsIdx := make([]int, 0, len(c.columns)-colIdx)
for i := colIdx; i < len(c.columns); i++ {
if c.columns[i] == c.columns[colIdx] {
refColsIdx = append(refColsIdx, i)
}
}
refColsIdx4Other := make([]int, 0, len(other.columns)-otherIdx)
for i := otherIdx; i < len(other.columns); i++ {
if other.columns[i] == other.columns[otherIdx] {
refColsIdx4Other = append(refColsIdx4Other, i)
}
}
// Swap columns from two chunks.
c.columns[colIdx], other.columns[otherIdx] = other.columns[otherIdx], c.columns[colIdx]
// Rebuild the reference.
for _, i := range refColsIdx {
c.MakeRef(colIdx, i)
}
for _, i := range refColsIdx4Other {
other.MakeRef(otherIdx, i)
}
}
// SwapColumns swaps columns with another Chunk.
func (c *Chunk) SwapColumns(other *Chunk) {
c.columns, other.columns = other.columns, c.columns
c.numVirtualRows, other.numVirtualRows = other.numVirtualRows, c.numVirtualRows
}
// SetNumVirtualRows sets the virtual row number for a Chunk.
// It should only be used when there exists no column in the Chunk.
func (c *Chunk) SetNumVirtualRows(numVirtualRows int) {
c.numVirtualRows = numVirtualRows
}
// Reset resets the chunk, so the memory it allocated can be reused.
// Make sure all the data in the chunk is not used anymore before you reuse this chunk.
func (c *Chunk) Reset() {
if c.columns == nil {
return
}
for _, col := range c.columns {
col.reset()
}
c.numVirtualRows = 0
}
// GrowAndReset resets the Chunk and doubles the capacity of the Chunk.
// The doubled capacity should not be larger than maxChunkSize.
// TODO: this method will be used in following PR.
func (c *Chunk) GrowAndReset(maxChunkSize int) {
if c.columns == nil {
return
}
newCap := reCalcCapacity(c, maxChunkSize)
if newCap <= c.capacity {
c.Reset()
return
}
c.capacity = newCap
c.columns = renewColumns(c.columns, newCap)
c.numVirtualRows = 0
}
// reCalcCapacity calculates the capacity for another Chunk based on the current
// Chunk. The new capacity is doubled only when the current Chunk is full.
func reCalcCapacity(c *Chunk, maxChunkSize int) int {
if c.NumRows() < c.capacity {
return c.capacity
}
return mathutil.Min(c.capacity*2, maxChunkSize)
}
// Capacity returns the capacity of the Chunk.
func (c *Chunk) Capacity() int {
return c.capacity
}
// NumCols returns the number of columns in the chunk.
func (c *Chunk) NumCols() int {
return len(c.columns)
}
// NumRows returns the number of rows in the chunk.
func (c *Chunk) NumRows() int {
if c.NumCols() == 0 {
return c.numVirtualRows
}
return c.columns[0].length
}
// GetRow gets the Row in the chunk with the row index.
func (c *Chunk) GetRow(idx int) Row {
return Row{c: c, idx: idx}
}
// AppendRow appends a row to the chunk.
func (c *Chunk) AppendRow(row Row) {
c.AppendPartialRow(0, row)
c.numVirtualRows++
}
// AppendPartialRow appends a row to the chunk.
func (c *Chunk) AppendPartialRow(colIdx int, row Row) {
for i, rowCol := range row.c.columns {
chkCol := c.columns[colIdx+i]
chkCol.appendNullBitmap(!rowCol.isNull(row.idx))
if rowCol.isFixed() {
elemLen := len(rowCol.elemBuf)
offset := row.idx * elemLen
chkCol.data = append(chkCol.data, rowCol.data[offset:offset+elemLen]...)
} else {
start, end := rowCol.offsets[row.idx], rowCol.offsets[row.idx+1]
chkCol.data = append(chkCol.data, rowCol.data[start:end]...)
chkCol.offsets = append(chkCol.offsets, int32(len(chkCol.data)))
}
chkCol.length++
}
}
// Append appends rows in [begin, end) in another Chunk to a Chunk.
func (c *Chunk) Append(other *Chunk, begin, end int) {
for colID, src := range other.columns {
dst := c.columns[colID]
if src.isFixed() {
elemLen := len(src.elemBuf)
dst.data = append(dst.data, src.data[begin*elemLen:end*elemLen]...)
} else {
beginOffset, endOffset := src.offsets[begin], src.offsets[end]
dst.data = append(dst.data, src.data[beginOffset:endOffset]...)
for i := begin; i < end; i++ {
dst.offsets = append(dst.offsets, dst.offsets[len(dst.offsets)-1]+src.offsets[i+1]-src.offsets[i])
}
}
for i := begin; i < end; i++ {
dst.appendNullBitmap(!src.isNull(i))
dst.length++
}
}
c.numVirtualRows += end - begin
}
// TruncateTo truncates rows from tail to head in a Chunk to "numRows" rows.
func (c *Chunk) TruncateTo(numRows int) {
for _, col := range c.columns {
if col.isFixed() {
elemLen := len(col.elemBuf)
col.data = col.data[:numRows*elemLen]
} else {
col.data = col.data[:col.offsets[numRows]]
col.offsets = col.offsets[:numRows+1]
}
for i := numRows; i < col.length; i++ {
if col.isNull(i) {
col.nullCount--
}
}
col.length = numRows
bitmapLen := (col.length + 7) / 8
col.nullBitmap = col.nullBitmap[:bitmapLen]
if col.length%8 != 0 {
// When we append null, we simply increment the nullCount,
// so we need to clear the unused bits in the last bitmap byte.
lastByte := col.nullBitmap[bitmapLen-1]
unusedBitsLen := 8 - uint(col.length%8)
lastByte <<= unusedBitsLen
lastByte >>= unusedBitsLen
col.nullBitmap[bitmapLen-1] = lastByte
}
}
c.numVirtualRows = numRows
}
// AppendNull appends a null value to the chunk.
func (c *Chunk) AppendNull(colIdx int) {
c.columns[colIdx].appendNull()
}
// AppendInt64 appends a int64 value to the chunk.
func (c *Chunk) AppendInt64(colIdx int, i int64) {
c.columns[colIdx].appendInt64(i)
}
// AppendUint64 appends a uint64 value to the chunk.
func (c *Chunk) AppendUint64(colIdx int, u uint64) {
c.columns[colIdx].appendUint64(u)
}
// AppendFloat32 appends a float32 value to the chunk.
func (c *Chunk) AppendFloat32(colIdx int, f float32) {
c.columns[colIdx].appendFloat32(f)
}
// AppendFloat64 appends a float64 value to the chunk.
func (c *Chunk) AppendFloat64(colIdx int, f float64) {
c.columns[colIdx].appendFloat64(f)
}
// AppendString appends a string value to the chunk.
func (c *Chunk) AppendString(colIdx int, str string) {
c.columns[colIdx].appendString(str)
}
// AppendBytes appends a bytes value to the chunk.
func (c *Chunk) AppendBytes(colIdx int, b []byte) {
c.columns[colIdx].appendBytes(b)
}
// AppendTime appends a Time value to the chunk.
// TODO: change the time structure so it can be directly written to memory.
func (c *Chunk) AppendTime(colIdx int, t types.Time) {
c.columns[colIdx].appendTime(t)
}
// AppendDuration appends a Duration value to the chunk.
func (c *Chunk) AppendDuration(colIdx int, dur types.Duration) {
c.columns[colIdx].appendDuration(dur)
}
// AppendMyDecimal appends a MyDecimal value to the chunk.
func (c *Chunk) AppendMyDecimal(colIdx int, dec *types.MyDecimal) {
c.columns[colIdx].appendMyDecimal(dec)
}
// AppendEnum appends an Enum value to the chunk.
func (c *Chunk) AppendEnum(colIdx int, enum types.Enum) {
c.columns[colIdx].appendNameValue(enum.Name, enum.Value)
}
// AppendSet appends a Set value to the chunk.
func (c *Chunk) AppendSet(colIdx int, set types.Set) {
c.columns[colIdx].appendNameValue(set.Name, set.Value)
}
// AppendJSON appends a JSON value to the chunk.
func (c *Chunk) AppendJSON(colIdx int, j json.BinaryJSON) {
c.columns[colIdx].appendJSON(j)
}
// AppendDatum appends a datum into the chunk.
func (c *Chunk) AppendDatum(colIdx int, d *types.Datum) {
switch d.Kind() {
case types.KindNull:
c.AppendNull(colIdx)
case types.KindInt64:
c.AppendInt64(colIdx, d.GetInt64())
case types.KindUint64:
c.AppendUint64(colIdx, d.GetUint64())
case types.KindFloat32:
c.AppendFloat32(colIdx, d.GetFloat32())
case types.KindFloat64:
c.AppendFloat64(colIdx, d.GetFloat64())
case types.KindString, types.KindBytes, types.KindBinaryLiteral, types.KindRaw, types.KindMysqlBit:
c.AppendBytes(colIdx, d.GetBytes())
case types.KindMysqlDecimal:
c.AppendMyDecimal(colIdx, d.GetMysqlDecimal())
case types.KindMysqlDuration:
c.AppendDuration(colIdx, d.GetMysqlDuration())
case types.KindMysqlEnum:
c.AppendEnum(colIdx, d.GetMysqlEnum())
case types.KindMysqlSet:
c.AppendSet(colIdx, d.GetMysqlSet())
case types.KindMysqlTime:
c.AppendTime(colIdx, d.GetMysqlTime())
case types.KindMysqlJSON:
c.AppendJSON(colIdx, d.GetMysqlJSON())
}
}
func writeTime(buf []byte, t types.Time) {
binary.BigEndian.PutUint16(buf, uint16(t.Time.Year()))
buf[2] = uint8(t.Time.Month())
buf[3] = uint8(t.Time.Day())
buf[4] = uint8(t.Time.Hour())
buf[5] = uint8(t.Time.Minute())
buf[6] = uint8(t.Time.Second())
binary.BigEndian.PutUint32(buf[8:], uint32(t.Time.Microsecond()))
buf[12] = t.Type
buf[13] = uint8(t.Fsp)
}
func readTime(buf []byte) types.Time {
year := int(binary.BigEndian.Uint16(buf))
month := int(buf[2])
day := int(buf[3])
hour := int(buf[4])
minute := int(buf[5])
second := int(buf[6])
microseconds := int(binary.BigEndian.Uint32(buf[8:]))
tp := buf[12]
fsp := int(buf[13])
return types.Time{
Time: types.FromDate(year, month, day, hour, minute, second, microseconds),
Type: tp,
Fsp: fsp,
}
}