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labels: shrink by making internals a single string

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This commit adds an alternate implementation for `labels.Labels`, behind
a build tag `stringlabels`.

Instead of storing label names and values as individual strings, they
are all concatenated into one string in this format:

    [len][name0][len][value0][len][name1][len][value1]...

The lengths are varint encoded so usually a single byte.

The previous `[]string` had 24 bytes of overhead for the slice and 16
for each label name and value; this one has 16 bytes overhead plus 1
for each name and value.

In `ScratchBuilder.Overwrite` and `Labels.Hash` we use an unsafe
conversion from string to byte slice. `Overwrite` is explicitly unsafe,
but for `Hash` this is a pure performance hack.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
pull/10991/head
Bryan Boreham 3 years ago
parent 3f7ba22bde
commit 6136ae67e0
2 changed files with 789 additions and 0 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
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  1. 2
      model/labels/labels.go
  2. 787
      model/labels/labels_string.go

2
model/labels/labels.go
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@ -11,6 +11,8 @@
// See the License for the specific language governing permissions and // See the License for the specific language governing permissions and
// limitations under the License. // limitations under the License.
//go:build !stringlabels
package labels package labels
import ( import (

787
model/labels/labels_string.go
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@ -0,0 +1,787 @@
// Copyright 2017 The Prometheus Authors
// 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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//go:build stringlabels
package labels
import (
"bytes"
"encoding/json"
"reflect"
"sort"
"strconv"
"unsafe"
"github.com/cespare/xxhash/v2"
"github.com/prometheus/common/model"
)
// Well-known label names used by Prometheus components.
const (
MetricName = "__name__"
AlertName = "alertname"
BucketLabel = "le"
InstanceName = "instance"
)
var seps = []byte{'\xff'}
// Label is a key/value pair of strings.
type Label struct {
Name, Value string
}
// Labels is implemented by a single flat string holding name/value pairs.
// Each name and value is preceded by its length in varint encoding.
// Names are in order.
type Labels struct {
data string
}
type labelSlice []Label
func (ls labelSlice) Len() int { return len(ls) }
func (ls labelSlice) Swap(i, j int) { ls[i], ls[j] = ls[j], ls[i] }
func (ls labelSlice) Less(i, j int) bool { return ls[i].Name < ls[j].Name }
func decodeSize(data string, index int) (int, int) {
var size int
for shift := uint(0); ; shift += 7 {
// Just panic if we go of the end of data, since all Labels strings are constructed internally and
// malformed data indicates a bug, or memory corruption.
b := data[index]
index++
size |= int(b&0x7F) << shift
if b < 0x80 {
break
}
}
return size, index
}
func decodeString(data string, index int) (string, int) {
var size int
size, index = decodeSize(data, index)
return data[index : index+size], index + size
}
func (ls Labels) String() string {
var b bytes.Buffer
b.WriteByte('{')
for i := 0; i < len(ls.data); {
if i > 0 {
b.WriteByte(',')
b.WriteByte(' ')
}
var name, value string
name, i = decodeString(ls.data, i)
value, i = decodeString(ls.data, i)
b.WriteString(name)
b.WriteByte('=')
b.WriteString(strconv.Quote(value))
}
b.WriteByte('}')
return b.String()
}
// Bytes returns ls as a byte slice.
// It uses non-printing characters and so should not be used for printing.
func (ls Labels) Bytes(buf []byte) []byte {
if cap(buf) < len(ls.data) {
buf = make([]byte, len(ls.data))
} else {
buf = buf[:len(ls.data)]
}
copy(buf, ls.data)
return buf
}
// MarshalJSON implements json.Marshaler.
func (ls Labels) MarshalJSON() ([]byte, error) {
return json.Marshal(ls.Map())
}
// UnmarshalJSON implements json.Unmarshaler.
func (ls *Labels) UnmarshalJSON(b []byte) error {
var m map[string]string
if err := json.Unmarshal(b, &m); err != nil {
return err
}
*ls = FromMap(m)
return nil
}
// MarshalYAML implements yaml.Marshaler.
func (ls Labels) MarshalYAML() (interface{}, error) {
return ls.Map(), nil
}
// IsZero implements yaml.IsZeroer - if we don't have this then 'omitempty' fields are always omitted.
func (ls Labels) IsZero() bool {
return len(ls.data) == 0
}
// UnmarshalYAML implements yaml.Unmarshaler.
func (ls *Labels) UnmarshalYAML(unmarshal func(interface{}) error) error {
var m map[string]string
if err := unmarshal(&m); err != nil {
return err
}
*ls = FromMap(m)
return nil
}
// MatchLabels returns a subset of Labels that matches/does not match with the provided label names based on the 'on' boolean.
// If on is set to true, it returns the subset of labels that match with the provided label names and its inverse when 'on' is set to false.
// TODO: This is only used in printing an error message
func (ls Labels) MatchLabels(on bool, names ...string) Labels {
b := NewBuilder(ls)
if on {
b.Keep(names...)
} else {
b.Del(MetricName)
b.Del(names...)
}
return b.Labels(EmptyLabels())
}
// Hash returns a hash value for the label set.
// Note: the result is not guaranteed to be consistent across different runs of Prometheus.
func (ls Labels) Hash() uint64 {
return xxhash.Sum64(yoloBytes(ls.data))
}
// HashForLabels returns a hash value for the labels matching the provided names.
// 'names' have to be sorted in ascending order.
func (ls Labels) HashForLabels(b []byte, names ...string) (uint64, []byte) {
b = b[:0]
j := 0
for i := 0; i < len(ls.data); {
var name, value string
name, i = decodeString(ls.data, i)
value, i = decodeString(ls.data, i)
for j < len(names) && names[j] < name {
j++
}
if j == len(names) {
break
}
if name == names[j] {
b = append(b, name...)
b = append(b, seps[0])
b = append(b, value...)
b = append(b, seps[0])
}
}
return xxhash.Sum64(b), b
}
// HashWithoutLabels returns a hash value for all labels except those matching
// the provided names.
// 'names' have to be sorted in ascending order.
func (ls Labels) HashWithoutLabels(b []byte, names ...string) (uint64, []byte) {
b = b[:0]
j := 0
for i := 0; i < len(ls.data); {
var name, value string
name, i = decodeString(ls.data, i)
value, i = decodeString(ls.data, i)
for j < len(names) && names[j] < name {
j++
}
if name == MetricName || (j < len(names) && name == names[j]) {
continue
}
b = append(b, name...)
b = append(b, seps[0])
b = append(b, value...)
b = append(b, seps[0])
}
return xxhash.Sum64(b), b
}
// BytesWithLabels is just as Bytes(), but only for labels matching names.
// 'names' have to be sorted in ascending order.
func (ls Labels) BytesWithLabels(buf []byte, names ...string) []byte {
b := buf[:0]
j := 0
for pos := 0; pos < len(ls.data); {
lName, newPos := decodeString(ls.data, pos)
_, newPos = decodeString(ls.data, newPos)
for j < len(names) && names[j] < lName {
j++
}
if j == len(names) {
break
}
if lName == names[j] {
b = append(b, ls.data[pos:newPos]...)
}
pos = newPos
}
return b
}
// BytesWithoutLabels is just as Bytes(), but only for labels not matching names.
// 'names' have to be sorted in ascending order.
func (ls Labels) BytesWithoutLabels(buf []byte, names ...string) []byte {
b := buf[:0]
j := 0
for pos := 0; pos < len(ls.data); {
lName, newPos := decodeString(ls.data, pos)
_, newPos = decodeString(ls.data, newPos)
for j < len(names) && names[j] < lName {
j++
}
if j == len(names) || lName != names[j] {
b = append(b, ls.data[pos:newPos]...)
}
pos = newPos
}
return b
}
// Copy returns a copy of the labels.
func (ls Labels) Copy() Labels {
buf := append([]byte{}, ls.data...)
return Labels{data: yoloString(buf)}
}
// Get returns the value for the label with the given name.
// Returns an empty string if the label doesn't exist.
func (ls Labels) Get(name string) string {
for i := 0; i < len(ls.data); {
var lName, lValue string
lName, i = decodeString(ls.data, i)
lValue, i = decodeString(ls.data, i)
if lName == name {
return lValue
}
}
return ""
}
// Has returns true if the label with the given name is present.
func (ls Labels) Has(name string) bool {
for i := 0; i < len(ls.data); {
var lName string
lName, i = decodeString(ls.data, i)
_, i = decodeString(ls.data, i)
if lName == name {
return true
}
}
return false
}
// HasDuplicateLabelNames returns whether ls has duplicate label names.
// It assumes that the labelset is sorted.
func (ls Labels) HasDuplicateLabelNames() (string, bool) {
var lName, prevName string
for i := 0; i < len(ls.data); {
lName, i = decodeString(ls.data, i)
_, i = decodeString(ls.data, i)
if lName == prevName {
return lName, true
}
prevName = lName
}
return "", false
}
// WithoutEmpty returns the labelset without empty labels.
// May return the same labelset.
func (ls Labels) WithoutEmpty() Labels {
for pos := 0; pos < len(ls.data); {
_, newPos := decodeString(ls.data, pos)
lValue, newPos := decodeString(ls.data, newPos)
if lValue != "" {
pos = newPos
continue
}
// Do not copy the slice until it's necessary.
// TODO: could optimise the case where all blanks are at the end.
// Note: we size the new buffer on the assumption there is exactly one blank value.
buf := make([]byte, pos, pos+(len(ls.data)-newPos))
copy(buf, ls.data[:pos]) // copy the initial non-blank labels
pos = newPos // move past the first blank value
for pos < len(ls.data) {
var newPos int
_, newPos = decodeString(ls.data, pos)
lValue, newPos = decodeString(ls.data, newPos)
if lValue != "" {
buf = append(buf, ls.data[pos:newPos]...)
}
pos = newPos
}
return Labels{data: yoloString(buf)}
}
return ls
}
// IsValid checks if the metric name or label names are valid.
func (ls Labels) IsValid() bool {
err := ls.Validate(func(l Label) error {
if l.Name == model.MetricNameLabel && !model.IsValidMetricName(model.LabelValue(l.Value)) {
return strconv.ErrSyntax
}
if !model.LabelName(l.Name).IsValid() || !model.LabelValue(l.Value).IsValid() {
return strconv.ErrSyntax
}
return nil
})
return err == nil
}
// Equal returns whether the two label sets are equal.
func Equal(ls, o Labels) bool {
return ls.data == o.data
}
// Map returns a string map of the labels.
func (ls Labels) Map() map[string]string {
m := make(map[string]string, len(ls.data)/10)
for i := 0; i < len(ls.data); {
var lName, lValue string
lName, i = decodeString(ls.data, i)
lValue, i = decodeString(ls.data, i)
m[lName] = lValue
}
return m
}
// EmptyLabels returns an empty Labels value, for convenience.
func EmptyLabels() Labels {
return Labels{}
}
func yoloString(b []byte) string {
return *((*string)(unsafe.Pointer(&b)))
}
func yoloBytes(s string) (b []byte) {
*(*string)(unsafe.Pointer(&b)) = s
(*reflect.SliceHeader)(unsafe.Pointer(&b)).Cap = len(s)
return
}
// New returns a sorted Labels from the given labels.
// The caller has to guarantee that all label names are unique.
func New(ls ...Label) Labels {
sort.Sort(labelSlice(ls))
size := labelsSize(ls)
buf := make([]byte, size)
marshalLabelsToSizedBuffer(ls, buf)
return Labels{data: yoloString(buf)}
}
// FromMap returns new sorted Labels from the given map.
func FromMap(m map[string]string) Labels {
l := make([]Label, 0, len(m))
for k, v := range m {
l = append(l, Label{Name: k, Value: v})
}
return New(l...)
}
// FromStrings creates new labels from pairs of strings.
func FromStrings(ss ...string) Labels {
if len(ss)%2 != 0 {
panic("invalid number of strings")
}
ls := make([]Label, 0, len(ss)/2)
for i := 0; i < len(ss); i += 2 {
ls = append(ls, Label{Name: ss[i], Value: ss[i+1]})
}
sort.Sort(labelSlice(ls))
return New(ls...)
}
// Compare compares the two label sets.
// The result will be 0 if a==b, <0 if a < b, and >0 if a > b.
// TODO: replace with Less function - Compare is never needed.
// TODO: just compare the underlying strings when we don't need alphanumeric sorting.
func Compare(a, b Labels) int {
l := len(a.data)
if len(b.data) < l {
l = len(b.data)
}
ia, ib := 0, 0
for ia < l {
var aName, bName string
aName, ia = decodeString(a.data, ia)
bName, ib = decodeString(b.data, ib)
if aName != bName {
if aName < bName {
return -1
}
return 1
}
var aValue, bValue string
aValue, ia = decodeString(a.data, ia)
bValue, ib = decodeString(b.data, ib)
if aValue != bValue {
if aValue < bValue {
return -1
}
return 1
}
}
// If all labels so far were in common, the set with fewer labels comes first.
return len(a.data) - len(b.data)
}
// Copy labels from b on top of whatever was in ls previously, reusing memory or expanding if needed.
func (ls *Labels) CopyFrom(b Labels) {
ls.data = b.data // strings are immutable
}
// IsEmpty returns true if ls represents an empty set of labels.
func (ls Labels) IsEmpty() bool {
return len(ls.data) == 0
}
// Len returns the number of labels; it is relatively slow.
func (ls Labels) Len() int {
count := 0
for i := 0; i < len(ls.data); {
var size int
size, i = decodeSize(ls.data, i)
i += size
size, i = decodeSize(ls.data, i)
i += size
count++
}
return count
}
// Range calls f on each label.
func (ls Labels) Range(f func(l Label)) {
for i := 0; i < len(ls.data); {
var lName, lValue string
lName, i = decodeString(ls.data, i)
lValue, i = decodeString(ls.data, i)
f(Label{Name: lName, Value: lValue})
}
}
// Validate calls f on each label. If f returns a non-nil error, then it returns that error cancelling the iteration.
func (ls Labels) Validate(f func(l Label) error) error {
for i := 0; i < len(ls.data); {
var lName, lValue string
lName, i = decodeString(ls.data, i)
lValue, i = decodeString(ls.data, i)
err := f(Label{Name: lName, Value: lValue})
if err != nil {
return err
}
}
return nil
}
// InternStrings calls intern on every string value inside ls, replacing them with what it returns.
func (ls *Labels) InternStrings(intern func(string) string) {
ls.data = intern(ls.data)
}
// ReleaseStrings calls release on every string value inside ls.
func (ls Labels) ReleaseStrings(release func(string)) {
release(ls.data)
}
// Builder allows modifying Labels.
type Builder struct {
base Labels
del []string
add []Label
}
// NewBuilder returns a new LabelsBuilder.
func NewBuilder(base Labels) *Builder {
b := &Builder{
del: make([]string, 0, 5),
add: make([]Label, 0, 5),
}
b.Reset(base)
return b
}
// Reset clears all current state for the builder.
func (b *Builder) Reset(base Labels) {
b.base = base
b.del = b.del[:0]
b.add = b.add[:0]
for i := 0; i < len(base.data); {
var lName, lValue string
lName, i = decodeString(base.data, i)
lValue, i = decodeString(base.data, i)
if lValue == "" {
b.del = append(b.del, lName)
}
}
}
// Del deletes the label of the given name.
func (b *Builder) Del(ns ...string) *Builder {
for _, n := range ns {
for i, a := range b.add {
if a.Name == n {
b.add = append(b.add[:i], b.add[i+1:]...)
}
}
b.del = append(b.del, n)
}
return b
}
// Keep removes all labels from the base except those with the given names.
func (b *Builder) Keep(ns ...string) *Builder {
Outer:
for i := 0; i < len(b.base.data); {
var lName string
lName, i = decodeString(b.base.data, i)
_, i = decodeString(b.base.data, i)
for _, n := range ns {
if lName == n {
continue Outer
}
}
b.del = append(b.del, lName)
}
return b
}
// Set the name/value pair as a label. A value of "" means delete that label.
func (b *Builder) Set(n, v string) *Builder {
if v == "" {
// Empty labels are the same as missing labels.
return b.Del(n)
}
for i, a := range b.add {
if a.Name == n {
b.add[i].Value = v
return b
}
}
b.add = append(b.add, Label{Name: n, Value: v})
return b
}
// Labels returns the labels from the builder, adding them to res if non-nil.
// Argument res can be the same as b.base, if caller wants to overwrite that slice.
// If no modifications were made, the original labels are returned.
func (b *Builder) Labels(res Labels) Labels {
if len(b.del) == 0 && len(b.add) == 0 {
return b.base
}
sort.Sort(labelSlice(b.add))
sort.Strings(b.del)
a, d := 0, 0
buf := make([]byte, 0, len(b.base.data)) // TODO: see if we can re-use the buffer from res.
for pos := 0; pos < len(b.base.data); {
oldPos := pos
var lName string
lName, pos = decodeString(b.base.data, pos)
_, pos = decodeString(b.base.data, pos)
for d < len(b.del) && b.del[d] < lName {
d++
}
if d < len(b.del) && b.del[d] == lName {
continue // This label has been deleted.
}
for ; a < len(b.add) && b.add[a].Name < lName; a++ {
buf = appendLabelTo(buf, &b.add[a]) // Insert label that was not in the base set.
}
if a < len(b.add) && b.add[a].Name == lName {
buf = appendLabelTo(buf, &b.add[a])
a++
continue // This label has been replaced.
}
buf = append(buf, b.base.data[oldPos:pos]...)
}
// We have come to the end of the base set; add any remaining labels.
for ; a < len(b.add); a++ {
buf = appendLabelTo(buf, &b.add[a])
}
return Labels{data: yoloString(buf)}
}
func marshalLabelsToSizedBuffer(lbls []Label, data []byte) int {
i := len(data)
for index := len(lbls) - 1; index >= 0; index-- {
size := marshalLabelToSizedBuffer(&lbls[index], data[:i])
i -= size
}
return len(data) - i
}
func marshalLabelToSizedBuffer(m *Label, data []byte) int {
i := len(data)
i -= len(m.Value)
copy(data[i:], m.Value)
i = encodeSize(data, i, len(m.Value))
i -= len(m.Name)
copy(data[i:], m.Name)
i = encodeSize(data, i, len(m.Name))
return len(data) - i
}
func sizeVarint(x uint64) (n int) {
// Most common case first
if x < 1<<7 {
return 1
}
if x >= 1<<56 {
return 9
}
if x >= 1<<28 {
x >>= 28
n = 4
}
if x >= 1<<14 {
x >>= 14
n += 2
}
if x >= 1<<7 {
n++
}
return n + 1
}
func encodeVarint(data []byte, offset int, v uint64) int {
offset -= sizeVarint(v)
base := offset
for v >= 1<<7 {
data[offset] = uint8(v&0x7f | 0x80)
v >>= 7
offset++
}
data[offset] = uint8(v)
return base
}
// Special code for the common case that a size is less than 128
func encodeSize(data []byte, offset, v int) int {
if v < 1<<7 {
offset--
data[offset] = uint8(v)
return offset
}
return encodeVarint(data, offset, uint64(v))
}
func labelsSize(lbls []Label) (n int) {
// we just encode name/value/name/value, without any extra tags or length bytes
for _, e := range lbls {
n += labelSize(&e)
}
return n
}
func labelSize(m *Label) (n int) {
// strings are encoded as length followed by contents.
l := len(m.Name)
n += l + sizeVarint(uint64(l))
l = len(m.Value)
n += l + sizeVarint(uint64(l))
return n
}
func appendLabelTo(buf []byte, m *Label) []byte {
size := labelSize(m)
sizeRequired := len(buf) + size
if cap(buf) >= sizeRequired {
buf = buf[:sizeRequired]
} else {
bufSize := cap(buf)
// Double size of buffer each time it needs to grow, to amortise copying cost.
for bufSize < sizeRequired {
bufSize = bufSize*2 + 1
}
newBuf := make([]byte, sizeRequired, bufSize)
copy(newBuf, buf)
buf = newBuf
}
marshalLabelToSizedBuffer(m, buf)
return buf
}
// ScratchBuilder allows efficient construction of a Labels from scratch.
type ScratchBuilder struct {
add []Label
output Labels
overwriteBuffer []byte
}
// NewScratchBuilder creates a ScratchBuilder initialized for Labels with n entries.
func NewScratchBuilder(n int) ScratchBuilder {
return ScratchBuilder{add: make([]Label, 0, n)}
}
func (b *ScratchBuilder) Reset() {
b.add = b.add[:0]
b.output = EmptyLabels()
}
// Add a name/value pair.
// Note if you Add the same name twice you will get a duplicate label, which is invalid.
func (b *ScratchBuilder) Add(name, value string) {
b.add = append(b.add, Label{Name: name, Value: value})
}
// Sort the labels added so far by name.
func (b *ScratchBuilder) Sort() {
sort.Sort(labelSlice(b.add))
}
// Asssign is for when you already have a Labels which you want this ScratchBuilder to return.
func (b *ScratchBuilder) Assign(l Labels) {
b.output = l
}
// Labels returns the name/value pairs added as a Labels object. Calling Add() after Labels() has no effect.
// Note: if you want them sorted, call Sort() first.
func (b *ScratchBuilder) Labels() Labels {
if b.output.IsEmpty() {
size := labelsSize(b.add)
buf := make([]byte, size)
marshalLabelsToSizedBuffer(b.add, buf)
b.output = Labels{data: yoloString(buf)}
}
return b.output
}
// Write the newly-built Labels out to ls, reusing an internal buffer.
// Callers must ensure that there are no other references to ls.
func (b *ScratchBuilder) Overwrite(ls *Labels) {
size := labelsSize(b.add)
if size <= cap(b.overwriteBuffer) {
b.overwriteBuffer = b.overwriteBuffer[:size]
} else {
b.overwriteBuffer = make([]byte, size)
}
marshalLabelsToSizedBuffer(b.add, b.overwriteBuffer)
ls.data = yoloString(b.overwriteBuffer)
}
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