forked from influxdata/influxdb
/
batch_timestamp.go
296 lines (245 loc) · 7.11 KB
/
batch_timestamp.go
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package tsm1
import (
"encoding/binary"
"fmt"
"math"
"unsafe"
"github.com/influxdata/influxdb/pkg/encoding/simple8b"
)
// TimeArrayEncodeAll encodes src into b, returning b and any error encountered.
// The returned slice may be of a different length and capacity to b.
//
// TimeArrayEncodeAll implements batch oriented versions of the three integer
// encoding types we support: uncompressed, simple8b and RLE.
//
// Timestamp values to be encoded should be sorted before encoding. When encoded,
// the values are first delta-encoded. The first value is the starting timestamp,
// subsequent values are the difference from the prior value.
//
// Important: TimeArrayEncodeAll modifies the contents of src by using it as
// scratch space for delta encoded values. It is NOT SAFE to use src after
// passing it into TimeArrayEncodeAll.
func TimeArrayEncodeAll(src []int64, b []byte) ([]byte, error) {
if len(src) == 0 {
return nil, nil // Nothing to do
}
var max, div = uint64(0), uint64(1e12)
// To prevent an allocation of the entire block we're encoding reuse the
// src slice to store the encoded deltas.
deltas := reintepretInt64ToUint64Slice(src)
if len(deltas) > 1 {
for i := len(deltas) - 1; i > 0; i-- {
deltas[i] = deltas[i] - deltas[i-1]
if deltas[i] > max {
max = deltas[i]
}
}
var rle = true
for i := 2; i < len(deltas); i++ {
if deltas[1] != deltas[i] {
rle = false
break
}
}
// Deltas are the same - encode with RLE
if rle {
// Large varints can take up to 10 bytes. We're storing 3 + 1
// type byte.
if len(b) < 31 && cap(b) >= 31 {
b = b[:31]
} else if len(b) < 31 {
b = append(b, make([]byte, 31-len(b))...)
}
// 4 high bits used for the encoding type
b[0] = byte(timeCompressedRLE) << 4
i := 1
// The first value
binary.BigEndian.PutUint64(b[i:], deltas[0])
i += 8
// The first delta, checking the divisor
// given all deltas are the same, we can do a single check for the divisor
v := deltas[1]
for div > 1 && v%div != 0 {
div /= 10
}
if div > 1 {
// 4 low bits are the log10 divisor
b[0] |= byte(math.Log10(float64(div)))
i += binary.PutUvarint(b[i:], deltas[1]/div)
} else {
i += binary.PutUvarint(b[i:], deltas[1])
}
// The number of times the delta is repeated
i += binary.PutUvarint(b[i:], uint64(len(deltas)))
return b[:i], nil
}
}
// We can't compress this time-range, the deltas exceed 1 << 60
if max > simple8b.MaxValue {
// Encode uncompressed.
sz := 1 + len(deltas)*8
if len(b) < sz && cap(b) >= sz {
b = b[:sz]
} else if len(b) < sz {
b = append(b, make([]byte, sz-len(b))...)
}
// 4 high bits of first byte store the encoding type for the block
b[0] = byte(timeUncompressed) << 4
for i, v := range deltas {
binary.BigEndian.PutUint64(b[1+i*8:1+i*8+8], v)
}
return b[:sz], nil
}
// find divisor only if we're compressing with simple8b
for i := 1; i < len(deltas) && div > 1; i++ {
// If our value is divisible by 10, break. Otherwise, try the next smallest divisor.
v := deltas[i]
for div > 1 && v%div != 0 {
div /= 10
}
}
// Only apply the divisor if it's greater than 1 since division is expensive.
if div > 1 {
for i := 1; i < len(deltas); i++ {
deltas[i] /= div
}
}
// Encode with simple8b - fist value is written unencoded using 8 bytes.
encoded, err := simple8b.EncodeAll(deltas[1:])
if err != nil {
return nil, err
}
sz := 1 + (len(encoded)+1)*8
if len(b) < sz && cap(b) >= sz {
b = b[:sz]
} else if len(b) < sz {
b = append(b, make([]byte, sz-len(b))...)
}
// 4 high bits of first byte store the encoding type for the block
b[0] = byte(timeCompressedPackedSimple) << 4
// 4 low bits are the log10 divisor
b[0] |= byte(math.Log10(float64(div)))
// Write the first value since it's not part of the encoded values
binary.BigEndian.PutUint64(b[1:9], deltas[0])
// Write the encoded values
for i, v := range encoded {
binary.BigEndian.PutUint64(b[9+i*8:9+i*8+8], v)
}
return b[:sz], nil
}
var (
timeBatchDecoderFunc = [...]func(b []byte, dst []int64) ([]int64, error){
timeBatchDecodeAllUncompressed,
timeBatchDecodeAllSimple,
timeBatchDecodeAllRLE,
timeBatchDecodeAllInvalid,
}
)
func TimeArrayDecodeAll(b []byte, dst []int64) ([]int64, error) {
if len(b) == 0 {
return []int64{}, nil
}
encoding := b[0] >> 4
if encoding > timeCompressedRLE {
encoding = 3 // timeBatchDecodeAllInvalid
}
return timeBatchDecoderFunc[encoding&3](b, dst)
}
func timeBatchDecodeAllUncompressed(b []byte, dst []int64) ([]int64, error) {
b = b[1:]
if len(b)&0x7 != 0 {
return []int64{}, fmt.Errorf("TimeArrayDecodeAll: expected multiple of 8 bytes")
}
count := len(b) / 8
if cap(dst) < count {
dst = make([]int64, count)
} else {
dst = dst[:count]
}
prev := uint64(0)
for i := range dst {
prev += binary.BigEndian.Uint64(b[i*8:])
dst[i] = int64(prev)
}
return dst, nil
}
func timeBatchDecodeAllSimple(b []byte, dst []int64) ([]int64, error) {
if len(b) < 9 {
return []int64{}, fmt.Errorf("TimeArrayDecodeAll: not enough data to decode packed timestamps")
}
div := uint64(math.Pow10(int(b[0] & 0xF))) // multiplier
count, err := simple8b.CountBytes(b[9:])
if err != nil {
return []int64{}, err
}
count += 1
if cap(dst) < count {
dst = make([]int64, count)
} else {
dst = dst[:count]
}
buf := *(*[]uint64)(unsafe.Pointer(&dst))
// first value
buf[0] = binary.BigEndian.Uint64(b[1:9])
n, err := simple8b.DecodeBytesBigEndian(buf[1:], b[9:])
if err != nil {
return []int64{}, err
}
if n != count-1 {
return []int64{}, fmt.Errorf("TimeArrayDecodeAll: unexpected number of values decoded; got=%d, exp=%d", n, count-1)
}
// Compute the prefix sum and scale the deltas back up
last := buf[0]
if div > 1 {
for i := 1; i < len(buf); i++ {
dgap := buf[i] * div
buf[i] = last + dgap
last = buf[i]
}
} else {
for i := 1; i < len(buf); i++ {
buf[i] += last
last = buf[i]
}
}
return dst, nil
}
func timeBatchDecodeAllRLE(b []byte, dst []int64) ([]int64, error) {
if len(b) < 9 {
return []int64{}, fmt.Errorf("TimeArrayDecodeAll: not enough data to decode RLE starting value")
}
var k, n int
// Lower 4 bits hold the 10 based exponent so we can scale the values back up
mod := int64(math.Pow10(int(b[k] & 0xF)))
k++
// Next 8 bytes is the starting timestamp
first := binary.BigEndian.Uint64(b[k:])
k += 8
// Next 1-10 bytes is our (scaled down by factor of 10) run length delta
delta, n := binary.Uvarint(b[k:])
if n <= 0 {
return []int64{}, fmt.Errorf("TimeArrayDecodeAll: invalid run length in decodeRLE")
}
k += n
// Scale the delta back up
delta *= uint64(mod)
// Last 1-10 bytes is how many times the value repeats
count, n := binary.Uvarint(b[k:])
if n <= 0 {
return []int64{}, fmt.Errorf("TimeDecoder: invalid repeat value in decodeRLE")
}
if cap(dst) < int(count) {
dst = make([]int64, count)
} else {
dst = dst[:count]
}
acc := first
for i := range dst {
dst[i] = int64(acc)
acc += delta
}
return dst, nil
}
func timeBatchDecodeAllInvalid(b []byte, _ []int64) ([]int64, error) {
return []int64{}, fmt.Errorf("unknown encoding %v", b[0]>>4)
}