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Fix reusing float histograms 

In https://github.com/prometheus/prometheus/pull/13276 we started reusing float histogram objects to reduce allocations in PromQL.
That PR introduces a bug where histogram pointers gets copied to the beginning of the histograms slice,
but are still kept in the end of the slice. When a new histogram is read into the last element,
it can overwrite a previous element because the pointer is the same.

This commit fixes the issue by moving outdated points to the end of the slice
so that we don't end up with duplicate pointers in the same buffer. In other words,
the slice gets rotated so that old objects can get reused.

Signed-off-by: Filip Petkovski <filip.petkovsky@gmail.com>
This commit is contained in:
Filip Petkovski 2023-12-14 11:28:15 +01:00
parent 69abd6d9f6
commit 1f69dcfa6b
No known key found for this signature in database
GPG Key ID: 431B0F2E85E42402
3 changed files with 82 additions and 22 deletions
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5
promql/engine.go
View File

@ -2052,7 +2052,12 @@ func (ev *evaluator) matrixIterSlice(
var drop int
for drop = 0; histograms[drop].T < mint; drop++ {
}
// Rotate the buffer around the drop index so that points before mint can be
// reused to store new histograms.
tail := make([]HPoint, drop)
copy(tail, histograms[:drop])
copy(histograms, histograms[drop:])
copy(histograms[len(histograms)-drop:], tail)
histograms = histograms[:len(histograms)-drop]
ev.currentSamples -= totalHPointSize(histograms)
// Only append points with timestamps after the last timestamp we have.

91
promql/engine_test.go
View File

@ -3169,28 +3169,75 @@ func TestNativeHistogramRate(t *testing.T) {
}
require.NoError(t, app.Commit())
queryString := fmt.Sprintf("rate(%s[1m])", seriesName)
qry, err := engine.NewInstantQuery(context.Background(), storage, nil, queryString, timestamp.Time(int64(5*time.Minute/time.Millisecond)))
require.NoError(t, err)
res := qry.Exec(context.Background())
require.NoError(t, res.Err)
vector, err := res.Vector()
require.NoError(t, err)
require.Len(t, vector, 1)
actualHistogram := vector[0].H
expectedHistogram := &histogram.FloatHistogram{
CounterResetHint: histogram.GaugeType,
Schema: 1,
ZeroThreshold: 0.001,
ZeroCount: 1. / 15.,
Count: 9. / 15.,
Sum: 1.226666666666667,
PositiveSpans: []histogram.Span{{Offset: 0, Length: 2}, {Offset: 1, Length: 2}},
PositiveBuckets: []float64{1. / 15., 1. / 15., 1. / 15., 1. / 15.},
NegativeSpans: []histogram.Span{{Offset: 0, Length: 2}, {Offset: 1, Length: 2}},
NegativeBuckets: []float64{1. / 15., 1. / 15., 1. / 15., 1. / 15.},
}
require.Equal(t, expectedHistogram, actualHistogram)
queryString := fmt.Sprintf("rate(%s[45s])", seriesName)
t.Run("instant_query", func(t *testing.T) {
qry, err := engine.NewInstantQuery(context.Background(), storage, nil, queryString, timestamp.Time(int64(5*time.Minute/time.Millisecond)))
require.NoError(t, err)
res := qry.Exec(context.Background())
require.NoError(t, res.Err)
vector, err := res.Vector()
require.NoError(t, err)
require.Len(t, vector, 1)
actualHistogram := vector[0].H
expectedHistogram := &histogram.FloatHistogram{
CounterResetHint: histogram.GaugeType,
Schema: 1,
ZeroThreshold: 0.001,
ZeroCount: 1. / 15.,
Count: 9. / 15.,
Sum: 1.2266666666666663,
PositiveSpans: []histogram.Span{{Offset: 0, Length: 2}, {Offset: 1, Length: 2}},
PositiveBuckets: []float64{1. / 15., 1. / 15., 1. / 15., 1. / 15.},
NegativeSpans: []histogram.Span{{Offset: 0, Length: 2}, {Offset: 1, Length: 2}},
NegativeBuckets: []float64{1. / 15., 1. / 15., 1. / 15., 1. / 15.},
}
require.Equal(t, expectedHistogram, actualHistogram)
})
t.Run("range_query", func(t *testing.T) {
step := 30 * time.Second
start := timestamp.Time(int64(5 * time.Minute / time.Millisecond))
end := start.Add(step)
qry, err := engine.NewRangeQuery(context.Background(), storage, nil, queryString, start, end, step)
require.NoError(t, err)
res := qry.Exec(context.Background())
require.NoError(t, res.Err)
matrix, err := res.Matrix()
require.NoError(t, err)
require.Len(t, matrix, 1)
require.Len(t, matrix[0].Histograms, 2)
actualHistograms := matrix[0].Histograms
expectedHistograms := []HPoint{{
T: 300000,
H: &histogram.FloatHistogram{
CounterResetHint: histogram.GaugeType,
Schema: 1,
ZeroThreshold: 0.001,
ZeroCount: 1. / 15.,
Count: 9. / 15.,
Sum: 1.2266666666666663,
PositiveSpans: []histogram.Span{{Offset: 0, Length: 2}, {Offset: 1, Length: 2}},
PositiveBuckets: []float64{1. / 15., 1. / 15., 1. / 15., 1. / 15.},
NegativeSpans: []histogram.Span{{Offset: 0, Length: 2}, {Offset: 1, Length: 2}},
NegativeBuckets: []float64{1. / 15., 1. / 15., 1. / 15., 1. / 15.},
},
}, {
T: 330000,
H: &histogram.FloatHistogram{
CounterResetHint: histogram.GaugeType,
Schema: 1,
ZeroThreshold: 0.001,
ZeroCount: 1. / 15.,
Count: 9. / 15.,
Sum: 1.2266666666666663,
PositiveSpans: []histogram.Span{{Offset: 0, Length: 2}, {Offset: 1, Length: 2}},
PositiveBuckets: []float64{1. / 15., 1. / 15., 1. / 15., 1. / 15.},
NegativeSpans: []histogram.Span{{Offset: 0, Length: 2}, {Offset: 1, Length: 2}},
NegativeBuckets: []float64{1. / 15., 1. / 15., 1. / 15., 1. / 15.},
},
}}
require.Equal(t, expectedHistograms, actualHistograms)
})
}
func TestNativeFloatHistogramRate(t *testing.T) {

8
tsdb/tsdbutil/histogram.go
View File

@ -30,6 +30,14 @@ func GenerateTestHistograms(n int) (r []*histogram.Histogram) {
return r
}
func GenerateTestHistogramsWithUnknownResetHint(n int) []*histogram.Histogram {
hs := GenerateTestHistograms(n)
for i := range hs {
hs[i].CounterResetHint = histogram.UnknownCounterReset
}
return hs
}
// GenerateTestHistogram but it is up to the user to set any known counter reset hint.
func GenerateTestHistogram(i int) *histogram.Histogram {
return &histogram.Histogram{