promql: fix smoothed interpolation across counter resets#17988
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roidelapluie merged 1 commit intoprometheus:mainfrom Feb 2, 2026
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promql: fix smoothed interpolation across counter resets#17988roidelapluie merged 1 commit intoprometheus:mainfrom
roidelapluie merged 1 commit intoprometheus:mainfrom
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Fix incorrect interpolation when counter resets occur in smoothed range selector evaluation. Previously, the asymmetric handling of counter resets (y1=0 on left edge, y2+=y1 on right edge) produced wrong values. Now uniformly set y1=0 when a counter reset is detected, correctly modeling the counter as starting from 0 post-reset. This fixes rate calculations across counter resets. For example, rate(metric[10s] smoothed) where metric goes from 100 to 10 (a reset) now correctly computes 0.666... by treating the counter as resetting to 0 rather than producing inflated values from the old behavior. Signed-off-by: Julien Pivotto <291750+roidelapluie@users.noreply.github.com>
krajorama
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LGTM. Seems obvious in hindsight.
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The upstream Prometheus change (prometheus/prometheus#17988) fixed incorrect interpolation when counter resets occur in smoothed range selector evaluation. The old behavior asymmetrically handled counter resets (y1=0 on left edge, y2+=y1 on right edge) which produced wrong values. The fix uniformly sets y1=0 when a counter reset is detected, correctly modeling the counter as starting from 0 post-reset. This updates our interpolate function to match the new behavior by removing the leftEdge parameter and adjusting test expectations accordingly. Signed-off-by: Julien Pivotto <291750+roidelapluie@users.noreply.github.com>
roidelapluie
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The upstream Prometheus change (prometheus/prometheus#17988) fixed incorrect interpolation when counter resets occur in smoothed range selector evaluation. The old behavior asymmetrically handled counter resets (y1=0 on left edge, y2+=y1 on right edge) which produced wrong values. The fix uniformly sets y1=0 when a counter reset is detected, correctly modeling the counter as starting from 0 post-reset. This updates our interpolate function to match the new behavior by removing the leftEdge parameter and adjusting test expectations accordingly. Signed-off-by: Julien Pivotto <291750+roidelapluie@users.noreply.github.com>
roidelapluie
added a commit
to grafana/mimir
that referenced
this pull request
Feb 5, 2026
The upstream Prometheus change (prometheus/prometheus#17988) fixed incorrect interpolation when counter resets occur in smoothed range selector evaluation. The old behavior asymmetrically handled counter resets (y1=0 on left edge, y2+=y1 on right edge) which produced wrong values. The fix uniformly sets y1=0 when a counter reset is detected, correctly modeling the counter as starting from 0 post-reset. This updates our interpolate function to match the new behavior by removing the leftEdge parameter and adjusting test expectations accordingly. Signed-off-by: Julien Pivotto <291750+roidelapluie@users.noreply.github.com>
roidelapluie
added a commit
to grafana/mimir
that referenced
this pull request
Feb 5, 2026
The upstream Prometheus change (prometheus/prometheus#17988) fixed incorrect interpolation when counter resets occur in smoothed range selector evaluation. The old behavior asymmetrically handled counter resets (y1=0 on left edge, y2+=y1 on right edge) which produced wrong values. The fix uniformly sets y1=0 when a counter reset is detected, correctly modeling the counter as starting from 0 post-reset. This updates our interpolate function to match the new behavior by removing the leftEdge parameter and adjusting test expectations accordingly. Signed-off-by: Julien Pivotto <291750+roidelapluie@users.noreply.github.com>
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Fix incorrect interpolation when counter resets occur in smoothed range selector evaluation. Previously, the asymmetric handling of counter resets (y1=0 on left edge, y2+=y1 on right edge) produced wrong values.
Now uniformly set y1=0 when a counter reset is detected, correctly modeling the counter as starting from 0 post-reset.
This fixes rate calculations across counter resets. For example, rate(metric[10s] smoothed) where metric goes from 100 to 10 (a reset) now correctly computes 0.666... by treating the counter as resetting to 0 rather than producing inflated values from the old behavior.
Which issue(s) does the PR fix:
Does this PR introduce a user-facing change?