MQE: fix issue where group_left / group_right could return series with incorrect labels
#10558
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… with incorrect labels
jhesketh
approved these changes
Feb 3, 2025
| @@ -416,7 +416,9 @@ func (g *GroupedVectorVectorBinaryOperation) manySideGroupKeyFunc() func(manySid | |||
| labelsToRemove := g.VectorMatching.Include | |||
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| if g.shouldRemoveMetricNameFromManySide() { | |||
| labelsToRemove = make([]string, 0, len(g.VectorMatching.Include)+1) | |||
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Not for this change, but should we consider using a string pool?
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Would be interesting to try, but I suspect the impact will be small given we tend to only use string slices for things that are created once per query (eg. this list of label names).
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What this PR does
This PR fixes a bug where MQE's implementation of
group_left/group_rightcould sometimes return incorrect labels for a series.In particular, this could happen if the number of additional labels in the
group_left(...)orgroup_right(...)modifier was not a power of two.VectorMatching.Includewas effectively being mutated inmanySideGroupKeyFuncto include__name__and drop the last label (rather than being copied to a new slice with__name__appended), and so the incorrect set of additional label names was used inoutputSeriesLabelsFunc.If the list of additional labels had a length that was a power of two, then the
appendinmanySideGroupKeyFunccaused a new underlying array to be created and so the bug was not triggered.Which issue(s) this PR fixes or relates to
(none)
Checklist
CHANGELOG.mdupdated - the order of entries should be[CHANGE],[FEATURE],[ENHANCEMENT],[BUGFIX].about-versioning.mdupdated with experimental features.