Ignore stale histograms for counter reset detection #14514
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The histogram stats decoder keeps track of the last seen histogram sample in order to properly detect counter resets. We are seeing an issue where a histogram with UnknownResetHint gets treated as a counter reset when it follows a stale histogram sample. I believe that this is incorrect since stale samples should be completely ignored in PromQL. As a result, they should not be stored in the histogram stats iterator and the counter reset detection needs to be done against the last non-stale sample. Signed-off-by: Filip Petkovski <[email protected]>
krajorama
reviewed
Jul 29, 2024
krajorama
reviewed
Jul 29, 2024
| expectedHints []histogram.CounterResetHint | ||
| }{ | ||
| { | ||
| name: "unknown counter reset triggers detection", |
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nit: you almost have 100% coverage, let's add the missing cases (this is for integer histograms):
{
name: "unknown counter reset at the beginning",
histograms: []*histogram.Histogram{
tsdbutil.GenerateTestHistogramWithHint(1, histogram.UnknownCounterReset),
},
expectedHints: []histogram.CounterResetHint{
histogram.NotCounterReset,
},
},
{
name: "detect real counter reset",
histograms: []*histogram.Histogram{
tsdbutil.GenerateTestHistogramWithHint(2, histogram.UnknownCounterReset),
tsdbutil.GenerateTestHistogramWithHint(1, histogram.UnknownCounterReset),
},
expectedHints: []histogram.CounterResetHint{
histogram.NotCounterReset,
histogram.CounterReset,
},
},
{
name: "detect real counter reset after stale NaN",
histograms: []*histogram.Histogram{
tsdbutil.GenerateTestHistogramWithHint(2, histogram.UnknownCounterReset),
{Sum: math.Float64frombits(value.StaleNaN)},
tsdbutil.GenerateTestHistogramWithHint(1, histogram.UnknownCounterReset),
},
expectedHints: []histogram.CounterResetHint{
histogram.NotCounterReset,
histogram.UnknownCounterReset,
histogram.CounterReset,
},
},
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Thanks for the suggestions, I added all these test cases and they seem to pass.
Signed-off-by: Filip Petkovski <[email protected]>
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The histogram stats decoder keeps track of the last seen histogram sample in order to properly detect counter resets. We are seeing an issue where a histogram with UnknownResetHint gets treated as a counter reset when it follows a stale histogram sample.
I believe that this is incorrect since stale samples should be completely ignored in PromQL. As a result, they should not be stored in the histogram stats iterator and the counter reset detection needs to be done against the last non-stale sample.