mirror of https://github.com/prometheus/prometheus
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
335 lines
9.9 KiB
335 lines
9.9 KiB
// Copyright 2021 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.
|
|
|
|
package chunkenc
|
|
|
|
import (
|
|
"math"
|
|
|
|
"github.com/prometheus/prometheus/model/histogram"
|
|
)
|
|
|
|
func writeHistogramChunkLayout(b *bstream, schema int32, zeroThreshold float64, positiveSpans, negativeSpans []histogram.Span) {
|
|
putZeroThreshold(b, zeroThreshold)
|
|
putVarbitInt(b, int64(schema))
|
|
putHistogramChunkLayoutSpans(b, positiveSpans)
|
|
putHistogramChunkLayoutSpans(b, negativeSpans)
|
|
}
|
|
|
|
func readHistogramChunkLayout(b *bstreamReader) (
|
|
schema int32, zeroThreshold float64,
|
|
positiveSpans, negativeSpans []histogram.Span,
|
|
err error,
|
|
) {
|
|
zeroThreshold, err = readZeroThreshold(b)
|
|
if err != nil {
|
|
return
|
|
}
|
|
|
|
v, err := readVarbitInt(b)
|
|
if err != nil {
|
|
return
|
|
}
|
|
schema = int32(v)
|
|
|
|
positiveSpans, err = readHistogramChunkLayoutSpans(b)
|
|
if err != nil {
|
|
return
|
|
}
|
|
|
|
negativeSpans, err = readHistogramChunkLayoutSpans(b)
|
|
if err != nil {
|
|
return
|
|
}
|
|
|
|
return
|
|
}
|
|
|
|
func putHistogramChunkLayoutSpans(b *bstream, spans []histogram.Span) {
|
|
putVarbitUint(b, uint64(len(spans)))
|
|
for _, s := range spans {
|
|
putVarbitUint(b, uint64(s.Length))
|
|
putVarbitInt(b, int64(s.Offset))
|
|
}
|
|
}
|
|
|
|
func readHistogramChunkLayoutSpans(b *bstreamReader) ([]histogram.Span, error) {
|
|
var spans []histogram.Span
|
|
num, err := readVarbitUint(b)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
for i := 0; i < int(num); i++ {
|
|
|
|
length, err := readVarbitUint(b)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
|
|
offset, err := readVarbitInt(b)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
|
|
spans = append(spans, histogram.Span{
|
|
Length: uint32(length),
|
|
Offset: int32(offset),
|
|
})
|
|
}
|
|
return spans, nil
|
|
}
|
|
|
|
// putZeroThreshold writes the zero threshold to the bstream. It stores typical
|
|
// values in just one byte, but needs 9 bytes for other values. In detail:
|
|
//
|
|
// * If the threshold is 0, store a single zero byte.
|
|
//
|
|
// * If the threshold is a power of 2 between (and including) 2^-243 and 2^10,
|
|
// take the exponent from the IEEE 754 representation of the threshold, which
|
|
// covers a range between (and including) -242 and 11. (2^-243 is 0.5*2^-242
|
|
// in IEEE 754 representation, and 2^10 is 0.5*2^11.) Add 243 to the exponent
|
|
// and store the result (which will be between 1 and 254) as a single
|
|
// byte. Note that small powers of two are preferred values for the zero
|
|
// threshold. The default value for the zero threshold is 2^-128 (or
|
|
// 0.5*2^-127 in IEEE 754 representation) and will therefore be encoded as a
|
|
// single byte (with value 116).
|
|
//
|
|
// * In all other cases, store 255 as a single byte, followed by the 8 bytes of
|
|
// the threshold as a float64, i.e. taking 9 bytes in total.
|
|
func putZeroThreshold(b *bstream, threshold float64) {
|
|
if threshold == 0 {
|
|
b.writeByte(0)
|
|
return
|
|
}
|
|
frac, exp := math.Frexp(threshold)
|
|
if frac != 0.5 || exp < -242 || exp > 11 {
|
|
b.writeByte(255)
|
|
b.writeBits(math.Float64bits(threshold), 64)
|
|
return
|
|
}
|
|
b.writeByte(byte(exp + 243))
|
|
}
|
|
|
|
// readZeroThreshold reads the zero threshold written with putZeroThreshold.
|
|
func readZeroThreshold(br *bstreamReader) (float64, error) {
|
|
b, err := br.ReadByte()
|
|
if err != nil {
|
|
return 0, err
|
|
}
|
|
switch b {
|
|
case 0:
|
|
return 0, nil
|
|
case 255:
|
|
v, err := br.readBits(64)
|
|
if err != nil {
|
|
return 0, err
|
|
}
|
|
return math.Float64frombits(v), nil
|
|
default:
|
|
return math.Ldexp(0.5, int(b)-243), nil
|
|
}
|
|
}
|
|
|
|
type bucketIterator struct {
|
|
spans []histogram.Span
|
|
span int // Span position of last yielded bucket.
|
|
bucket int // Bucket position within span of last yielded bucket.
|
|
idx int // Bucket index (globally across all spans) of last yielded bucket.
|
|
}
|
|
|
|
func newBucketIterator(spans []histogram.Span) *bucketIterator {
|
|
b := bucketIterator{
|
|
spans: spans,
|
|
span: 0,
|
|
bucket: -1,
|
|
idx: -1,
|
|
}
|
|
if len(spans) > 0 {
|
|
b.idx += int(spans[0].Offset)
|
|
}
|
|
return &b
|
|
}
|
|
|
|
func (b *bucketIterator) Next() (int, bool) {
|
|
// We're already out of bounds.
|
|
if b.span >= len(b.spans) {
|
|
return 0, false
|
|
}
|
|
try:
|
|
if b.bucket < int(b.spans[b.span].Length-1) { // Try to move within same span.
|
|
b.bucket++
|
|
b.idx++
|
|
return b.idx, true
|
|
} else if b.span < len(b.spans)-1 { // Try to move from one span to the next.
|
|
b.span++
|
|
b.idx += int(b.spans[b.span].Offset + 1)
|
|
b.bucket = 0
|
|
if b.spans[b.span].Length == 0 {
|
|
// Pathological case that should never happen. We can't use this span, let's try again.
|
|
goto try
|
|
}
|
|
return b.idx, true
|
|
}
|
|
// We're out of options.
|
|
return 0, false
|
|
}
|
|
|
|
// An Interjection describes how many new buckets have to be introduced before
|
|
// processing the pos'th delta from the original slice.
|
|
type Interjection struct {
|
|
pos int
|
|
num int
|
|
}
|
|
|
|
// compareSpans returns the interjections to convert a slice of deltas to a new
|
|
// slice representing an expanded set of buckets, or false if incompatible
|
|
// (e.g. if buckets were removed).
|
|
//
|
|
// Example:
|
|
//
|
|
// Let's say the old buckets look like this:
|
|
//
|
|
// span syntax: [offset, length]
|
|
// spans : [ 0 , 2 ] [2,1] [ 3 , 2 ] [3,1] [1,1]
|
|
// bucket idx : [0] [1] 2 3 [4] 5 6 7 [8] [9] 10 11 12 [13] 14 [15]
|
|
// raw values 6 3 3 2 4 5 1
|
|
// deltas 6 -3 0 -1 2 1 -4
|
|
//
|
|
// But now we introduce a new bucket layout. (Carefully chosen example where we
|
|
// have a span appended, one unchanged[*], one prepended, and two merge - in
|
|
// that order.)
|
|
//
|
|
// [*] unchanged in terms of which bucket indices they represent. but to achieve
|
|
// that, their offset needs to change if "disrupted" by spans changing ahead of
|
|
// them
|
|
//
|
|
// \/ this one is "unchanged"
|
|
// spans : [ 0 , 3 ] [1,1] [ 1 , 4 ] [ 3 , 3 ]
|
|
// bucket idx : [0] [1] [2] 3 [4] 5 [6] [7] [8] [9] 10 11 12 [13] [14] [15]
|
|
// raw values 6 3 0 3 0 0 2 4 5 0 1
|
|
// deltas 6 -3 -3 3 -3 0 2 2 1 -5 1
|
|
// delta mods: / \ / \ / \
|
|
//
|
|
// Note that whenever any new buckets are introduced, the subsequent "old"
|
|
// bucket needs to readjust its delta to the new base of 0. Thus, for the caller
|
|
// who wants to transform the set of original deltas to a new set of deltas to
|
|
// match a new span layout that adds buckets, we simply need to generate a list
|
|
// of interjections.
|
|
//
|
|
// Note: Within compareSpans we don't have to worry about the changes to the
|
|
// spans themselves, thanks to the iterators we get to work with the more useful
|
|
// bucket indices (which of course directly correspond to the buckets we have to
|
|
// adjust).
|
|
func compareSpans(a, b []histogram.Span) ([]Interjection, bool) {
|
|
ai := newBucketIterator(a)
|
|
bi := newBucketIterator(b)
|
|
|
|
var interjections []Interjection
|
|
|
|
// When inter.num becomes > 0, this becomes a valid interjection that
|
|
// should be yielded when we finish a streak of new buckets.
|
|
var inter Interjection
|
|
|
|
av, aOK := ai.Next()
|
|
bv, bOK := bi.Next()
|
|
loop:
|
|
for {
|
|
switch {
|
|
case aOK && bOK:
|
|
switch {
|
|
case av == bv: // Both have an identical value. move on!
|
|
// Finish WIP interjection and reset.
|
|
if inter.num > 0 {
|
|
interjections = append(interjections, inter)
|
|
}
|
|
inter.num = 0
|
|
av, aOK = ai.Next()
|
|
bv, bOK = bi.Next()
|
|
inter.pos++
|
|
case av < bv: // b misses a value that is in a.
|
|
return interjections, false
|
|
case av > bv: // a misses a value that is in b. Forward b and recompare.
|
|
inter.num++
|
|
bv, bOK = bi.Next()
|
|
}
|
|
case aOK && !bOK: // b misses a value that is in a.
|
|
return interjections, false
|
|
case !aOK && bOK: // a misses a value that is in b. Forward b and recompare.
|
|
inter.num++
|
|
bv, bOK = bi.Next()
|
|
default: // Both iterators ran out. We're done.
|
|
if inter.num > 0 {
|
|
interjections = append(interjections, inter)
|
|
}
|
|
break loop
|
|
}
|
|
}
|
|
|
|
return interjections, true
|
|
}
|
|
|
|
// interject merges 'in' with the provided interjections and writes them into
|
|
// 'out', which must already have the appropriate length.
|
|
func interject(in, out []int64, interjections []Interjection) []int64 {
|
|
var (
|
|
j int // Position in out.
|
|
v int64 // The last value seen.
|
|
interj int // The next interjection to process.
|
|
)
|
|
for i, d := range in {
|
|
if interj < len(interjections) && i == interjections[interj].pos {
|
|
|
|
// We have an interjection!
|
|
// Add interjection.num new delta values such that their
|
|
// bucket values equate 0.
|
|
out[j] = int64(-v)
|
|
j++
|
|
for x := 1; x < interjections[interj].num; x++ {
|
|
out[j] = 0
|
|
j++
|
|
}
|
|
interj++
|
|
|
|
// Now save the value from the input. The delta value we
|
|
// should save is the original delta value + the last
|
|
// value of the point before the interjection (to undo
|
|
// the delta that was introduced by the interjection).
|
|
out[j] = d + v
|
|
j++
|
|
v = d + v
|
|
continue
|
|
}
|
|
|
|
// If there was no interjection, the original delta is still
|
|
// valid.
|
|
out[j] = d
|
|
j++
|
|
v += d
|
|
}
|
|
switch interj {
|
|
case len(interjections):
|
|
// All interjections processed. Nothing more to do.
|
|
case len(interjections) - 1:
|
|
// One more interjection to process at the end.
|
|
out[j] = int64(-v)
|
|
j++
|
|
for x := 1; x < interjections[interj].num; x++ {
|
|
out[j] = 0
|
|
j++
|
|
}
|
|
default:
|
|
panic("unprocessed interjections left")
|
|
}
|
|
return out
|
|
}
|