Merge pull request #1627 from prometheus/release-1.20

Merge Release 1.20 back to main
This commit is contained in:
Arthur Silva Sens 2024-09-17 10:39:34 +02:00 committed by GitHub
commit 39e7c23b95
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3 changed files with 81 additions and 29 deletions

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@ -1,5 +1,11 @@
## Unreleased ## Unreleased
* [BUGFIX] histograms: Fix possible data race when appending exemplars vs metrics gather. #1623
## 1.20.3 / 2024-09-05
* [BUGFIX] histograms: Fix possible data race when appending exemplars. #1608
## 1.20.2 / 2024-08-23 ## 1.20.2 / 2024-08-23
* [BUGFIX] promhttp: Unset Content-Encoding header when data is uncompressed. #1596 * [BUGFIX] promhttp: Unset Content-Encoding header when data is uncompressed. #1596

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@ -844,9 +844,7 @@ func (h *histogram) Write(out *dto.Metric) error {
}} }}
} }
// If exemplars are not configured, the cap will be 0. if h.nativeExemplars.isEnabled() {
// So append is not needed in this case.
if cap(h.nativeExemplars.exemplars) > 0 {
h.nativeExemplars.Lock() h.nativeExemplars.Lock()
his.Exemplars = append(his.Exemplars, h.nativeExemplars.exemplars...) his.Exemplars = append(his.Exemplars, h.nativeExemplars.exemplars...)
h.nativeExemplars.Unlock() h.nativeExemplars.Unlock()
@ -1658,10 +1656,17 @@ func addAndResetCounts(hot, cold *histogramCounts) {
type nativeExemplars struct { type nativeExemplars struct {
sync.Mutex sync.Mutex
// Time-to-live for exemplars, it is set to -1 if exemplars are disabled, that is NativeHistogramMaxExemplars is below 0.
// The ttl is used on insertion to remove an exemplar that is older than ttl, if present.
ttl time.Duration ttl time.Duration
exemplars []*dto.Exemplar exemplars []*dto.Exemplar
} }
func (n *nativeExemplars) isEnabled() bool {
return n.ttl != -1
}
func makeNativeExemplars(ttl time.Duration, maxCount int) nativeExemplars { func makeNativeExemplars(ttl time.Duration, maxCount int) nativeExemplars {
if ttl == 0 { if ttl == 0 {
ttl = 5 * time.Minute ttl = 5 * time.Minute
@ -1673,6 +1678,7 @@ func makeNativeExemplars(ttl time.Duration, maxCount int) nativeExemplars {
if maxCount < 0 { if maxCount < 0 {
maxCount = 0 maxCount = 0
ttl = -1
} }
return nativeExemplars{ return nativeExemplars{
@ -1682,20 +1688,18 @@ func makeNativeExemplars(ttl time.Duration, maxCount int) nativeExemplars {
} }
func (n *nativeExemplars) addExemplar(e *dto.Exemplar) { func (n *nativeExemplars) addExemplar(e *dto.Exemplar) {
if cap(n.exemplars) == 0 { if !n.isEnabled() {
return return
} }
n.Lock() n.Lock()
defer n.Unlock() defer n.Unlock()
// The index where to insert the new exemplar.
var nIdx int = -1
// When the number of exemplars has not yet exceeded or // When the number of exemplars has not yet exceeded or
// is equal to cap(n.exemplars), then // is equal to cap(n.exemplars), then
// insert the new exemplar directly. // insert the new exemplar directly.
if len(n.exemplars) < cap(n.exemplars) { if len(n.exemplars) < cap(n.exemplars) {
var nIdx int
for nIdx = 0; nIdx < len(n.exemplars); nIdx++ { for nIdx = 0; nIdx < len(n.exemplars); nIdx++ {
if *e.Value < *n.exemplars[nIdx].Value { if *e.Value < *n.exemplars[nIdx].Value {
break break
@ -1705,15 +1709,44 @@ func (n *nativeExemplars) addExemplar(e *dto.Exemplar) {
return return
} }
if len(n.exemplars) == 1 {
// When the number of exemplars is 1, then
// replace the existing exemplar with the new exemplar.
n.exemplars[0] = e
return
}
// From this point on, the number of exemplars is greater than 1.
// When the number of exemplars exceeds the limit, remove one exemplar. // When the number of exemplars exceeds the limit, remove one exemplar.
var ( var (
rIdx int // The index where to remove the old exemplar. ot = time.Time{} // Oldest timestamp seen. Initial value doesn't matter as we replace it due to otIdx == -1 in the loop.
ot = time.Now() // Oldest timestamp seen.
otIdx = -1 // Index of the exemplar with the oldest timestamp. otIdx = -1 // Index of the exemplar with the oldest timestamp.
md = -1.0 // Logarithm of the delta of the closest pair of exemplars. md = -1.0 // Logarithm of the delta of the closest pair of exemplars.
mdIdx = -1 // Index of the older exemplar within the closest pair.
// The insertion point of the new exemplar in the exemplars slice after insertion.
// This is calculated purely based on the order of the exemplars by value.
// nIdx == len(n.exemplars) means the new exemplar is to be inserted after the end.
nIdx = -1
// rIdx is ultimately the index for the exemplar that we are replacing with the new exemplar.
// The aim is to keep a good spread of exemplars by value and not let them bunch up too much.
// It is calculated in 3 steps:
// 1. First we set rIdx to the index of the older exemplar within the closest pair by value.
// That is the following will be true (on log scale):
// either the exemplar pair on index (rIdx-1, rIdx) or (rIdx, rIdx+1) will have
// the closest values to each other from all pairs.
// For example, suppose the values are distributed like this:
// |-----------x-------------x----------------x----x-----|
// ^--rIdx as this is older.
// Or like this:
// |-----------x-------------x----------------x----x-----|
// ^--rIdx as this is older.
// 2. If there is an exemplar that expired, then we simple reset rIdx to that index.
// 3. We check if by inserting the new exemplar we would create a closer pair at
// (nIdx-1, nIdx) or (nIdx, nIdx+1) and set rIdx to nIdx-1 or nIdx accordingly to
// keep the spread of exemplars by value; otherwise we keep rIdx as it is.
rIdx = -1
cLog float64 // Logarithm of the current exemplar. cLog float64 // Logarithm of the current exemplar.
pLog float64 // Logarithm of the previous exemplar. pLog float64 // Logarithm of the previous exemplar.
) )
@ -1726,7 +1759,7 @@ func (n *nativeExemplars) addExemplar(e *dto.Exemplar) {
} }
// Find the index at which to insert new the exemplar. // Find the index at which to insert new the exemplar.
if *e.Value <= *exemplar.Value && nIdx == -1 { if nIdx == -1 && *e.Value <= *exemplar.Value {
nIdx = i nIdx = i
} }
@ -1738,11 +1771,13 @@ func (n *nativeExemplars) addExemplar(e *dto.Exemplar) {
} }
diff := math.Abs(cLog - pLog) diff := math.Abs(cLog - pLog)
if md == -1 || diff < md { if md == -1 || diff < md {
// The closest exemplar pair is at index: i-1, i.
// Choose the exemplar with the older timestamp for replacement.
md = diff md = diff
if n.exemplars[i].Timestamp.AsTime().Before(n.exemplars[i-1].Timestamp.AsTime()) { if n.exemplars[i].Timestamp.AsTime().Before(n.exemplars[i-1].Timestamp.AsTime()) {
mdIdx = i rIdx = i
} else { } else {
mdIdx = i - 1 rIdx = i - 1
} }
} }
@ -1753,8 +1788,12 @@ func (n *nativeExemplars) addExemplar(e *dto.Exemplar) {
if nIdx == -1 { if nIdx == -1 {
nIdx = len(n.exemplars) nIdx = len(n.exemplars)
} }
// Here, we have the following relationships:
// n.exemplars[nIdx-1].Value < e.Value (if nIdx > 0)
// e.Value <= n.exemplars[nIdx].Value (if nIdx < len(n.exemplars))
if otIdx != -1 && e.Timestamp.AsTime().Sub(ot) > n.ttl { if otIdx != -1 && e.Timestamp.AsTime().Sub(ot) > n.ttl {
// If the oldest exemplar has expired, then replace it with the new exemplar.
rIdx = otIdx rIdx = otIdx
} else { } else {
// In the previous for loop, when calculating the closest pair of exemplars, // In the previous for loop, when calculating the closest pair of exemplars,
@ -1764,24 +1803,27 @@ func (n *nativeExemplars) addExemplar(e *dto.Exemplar) {
if nIdx > 0 { if nIdx > 0 {
diff := math.Abs(elog - math.Log(n.exemplars[nIdx-1].GetValue())) diff := math.Abs(elog - math.Log(n.exemplars[nIdx-1].GetValue()))
if diff < md { if diff < md {
// The value we are about to insert is closer to the previous exemplar at the insertion point than what we calculated before in rIdx.
// v--rIdx
// |-----------x-n-----------x----------------x----x-----|
// nIdx-1--^ ^--new exemplar value
// Do not make the spread worse, replace nIdx-1 and not rIdx.
md = diff md = diff
mdIdx = nIdx rIdx = nIdx - 1
if n.exemplars[nIdx-1].Timestamp.AsTime().Before(e.Timestamp.AsTime()) {
mdIdx = nIdx - 1
}
} }
} }
if nIdx < len(n.exemplars) { if nIdx < len(n.exemplars) {
diff := math.Abs(math.Log(n.exemplars[nIdx].GetValue()) - elog) diff := math.Abs(math.Log(n.exemplars[nIdx].GetValue()) - elog)
if diff < md { if diff < md {
mdIdx = nIdx // The value we are about to insert is closer to the next exemplar at the insertion point than what we calculated before in rIdx.
if n.exemplars[nIdx].Timestamp.AsTime().Before(e.Timestamp.AsTime()) { // v--rIdx
mdIdx = nIdx // |-----------x-----------n-x----------------x----x-----|
// new exemplar value--^ ^--nIdx
// Do not make the spread worse, replace nIdx-1 and not rIdx.
rIdx = nIdx
} }
} }
} }
rIdx = mdIdx
}
// Adjust the slice according to rIdx and nIdx. // Adjust the slice according to rIdx and nIdx.
switch { switch {

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@ -1049,10 +1049,14 @@ func TestNativeHistogramConcurrency(t *testing.T) {
go func(vals []float64) { go func(vals []float64) {
start.Wait() start.Wait()
for _, v := range vals { for i, v := range vals {
// An observation every 1 to 10 seconds. // An observation every 1 to 10 seconds.
atomic.AddInt64(&ts, rand.Int63n(10)+1) atomic.AddInt64(&ts, rand.Int63n(10)+1)
if i%2 == 0 {
his.Observe(v) his.Observe(v)
} else {
his.(ExemplarObserver).ObserveWithExemplar(v, Labels{"foo": "bar"})
}
} }
end.Done() end.Done()
}(vals) }(vals)