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promql: Fix wrongly scoped range vectors

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Fixes #11708.

If a range vector is fixen in time with the @ modifier, it gets still
moved around for different steps in a range query. Since no additional
points are retrieved from the TSDB, this leads to steadily emptying
the range, leading to the weird behavior described in isse #11708.

This only happens for functions listed in `AtModifierUnsafeFunctions`,
and the only of those that takes a range vector is `predict_linear`,
which is the reason why we see it only for this particular function.

Signed-off-by: beorn7 <beorn@grafana.com>
This commit is contained in:
beorn7 2024-02-07 18:07:51 +01:00
parent 384ab025e0
commit 86d7618d84
1 changed files with 8 additions and 4 deletions
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12
promql/engine.go
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@ -1494,10 +1494,14 @@ func (ev *evaluator) eval(expr parser.Expr) (parser.Value, annotations.Annotatio
otherInArgs[j][0].F = otherArgs[j][0].Floats[step].F
}
}
maxt := ts - offset
mint := maxt - selRange
// Evaluate the matrix selector for this series for this step.
floats, histograms = ev.matrixIterSlice(it, mint, maxt, floats, histograms)
// Evaluate the matrix selector for this series
// for this step, but only if this is the 1st
// iteration or no @ modifier has been used.
if ts == ev.startTimestamp || selVS.Timestamp == nil {
maxt := ts - offset
mint := maxt - selRange
floats, histograms = ev.matrixIterSlice(it, mint, maxt, floats, histograms)
}
if len(floats)+len(histograms) == 0 {
continue
}