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inhibit: preserve source-only matches in equal-label index #5449

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inhibit: preserve source-only matches in equal-label index #5449

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inhibit: preserve source-only matches in equal-label index
sueun-dev Aug 14, 2026
8067c18
inhibit: keep equal-label source index complete
sueun-dev Aug 28, 2026
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24 changes: 23 additions & 1 deletion inhibit/inhibit.go
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Original file line number Diff line number Diff line change
Expand Up @@ -397,6 +397,24 @@ func (r *InhibitRule) findEqualSourceAlert(lset model.LabelSet, now time.Time) (
return nil, false
}

func (r *InhibitRule) findEqualSourceAlertFromCache(lset model.LabelSet, excludeTwoSidedMatch bool, now time.Time) (*types.Alert, bool) {
equalsFP := r.fingerprintEquals(lset)
for _, alert := range r.scache.List() {
if alert.ResolvedAt(now) {
continue
}
if r.fingerprintEquals(alert.Labels) != equalsFP {
continue
}
if excludeTwoSidedMatch && r.TargetMatchers.Matches(alert.Labels) {
continue
}
return alert, true
}

return nil, false
}

@siavashs siavashs Aug 28, 2026

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This scans the whole cache whenever the indexed source is two-sided which is O(number of source alerts), allocates a copy, locks the shared cache mutex, etc.
This is basically skipping the optimisations #4607 introduced.
Also the current benchmark matrix does not cover this case.


func (r *InhibitRule) gcCallback(alerts []*types.Alert) {
for _, a := range alerts {
fp := r.fingerprintEquals(a.Labels)
Expand All @@ -412,7 +430,11 @@ func (r *InhibitRule) hasEqual(lset model.LabelSet, excludeTwoSidedMatch bool, n
equal, found := r.findEqualSourceAlert(lset, now)
if found {
if excludeTwoSidedMatch && r.TargetMatchers.Matches(equal.Labels) {
return model.Fingerprint(0), false
equal, found = r.findEqualSourceAlertFromCache(lset, excludeTwoSidedMatch, now)

@siavashs siavashs Aug 28, 2026

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The new method is only called when a source alert is found in cache initially but is disqualified.
The index can be absent while same-equal active sources remain.
gcCallback deletes the whole equal-label key when any alert in that bucket is collected.
So we need a regression test where GC removes a non-indexed same-equal alert while a source-only alert remains active. Ideally the index should remove a specific source fingerprint rather than deleting the bucket.

if !found {
return model.Fingerprint(0), false
}
return equal.Fingerprint(), true
}
return equal.Fingerprint(), found
}
Expand Down
47 changes: 38 additions & 9 deletions inhibit/inhibit_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -57,11 +57,13 @@ func TestInhibitRuleHasEqual(t *testing.T) {

now := time.Now()
cases := []struct {
name string
initial map[model.Fingerprint]*alert.Alert
equal model.LabelNames
input model.LabelSet
result bool
name string
initial map[model.Fingerprint]*alert.Alert
equal model.LabelNames
targetMatchers labels.Matchers
input model.LabelSet
excludeTwoSidedMatch bool
result bool
}{
{
name: "no source alerts",
Expand Down Expand Up @@ -141,14 +143,41 @@ func TestInhibitRuleHasEqual(t *testing.T) {
input: model.LabelSet{"a": "b"},
result: false,
},
{
name: "matching source-only alert still inhibits when newest equal source is two-sided",
initial: map[model.Fingerprint]*alert.Alert{
1: {
Alert: model.Alert{
Labels: model.LabelSet{"s": "1", "e": "1"},
StartsAt: now.Add(-time.Minute),
EndsAt: now.Add(time.Hour),
},
},
2: {
Alert: model.Alert{
Labels: model.LabelSet{"s": "1", "t": "1", "e": "1"},
StartsAt: now.Add(-time.Minute),
EndsAt: now.Add(2 * time.Hour),
},
},
},
equal: model.LabelNames{"e"},
targetMatchers: labels.Matchers{{Type: labels.MatchEqual, Name: "t", Value: "1"}},
input: model.LabelSet{"s": "1", "t": "1", "e": "1"},
// The indexed two-sided source must be ignored, but the source-only
// alert with the same equal labels should still inhibit the target.
excludeTwoSidedMatch: true,
result: true,
},
}

for _, c := range cases {
t.Run(c.name, func(t *testing.T) {
r := &InhibitRule{
Equal: map[model.LabelName]struct{}{},
scache: store.NewAlerts(),
sindex: newIndex(),
Equal: map[model.LabelName]struct{}{},
TargetMatchers: c.targetMatchers,
scache: store.NewAlerts(),
sindex: newIndex(),
}
for _, ln := range c.equal {
r.Equal[ln] = struct{}{}
Expand All @@ -158,7 +187,7 @@ func TestInhibitRuleHasEqual(t *testing.T) {
r.updateIndex(v)
}

if _, have := r.hasEqual(c.input, false, time.Now()); have != c.result {
if _, have := r.hasEqual(c.input, c.excludeTwoSidedMatch, time.Now()); have != c.result {
t.Errorf("Unexpected result %t, expected %t", have, c.result)
}
})
Expand Down
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