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feat(model): add jitter to next_check_at scheduling to avoid thundering herd #3821

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feat(model): add jitter to next_check_at scheduling to avoid thundering herd #3821

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51e826e
add jitter to next_check_at scheduling to avoid thundering herd
Oct 8, 2025
796802f
feat: add config variable for polling jitter
gabrielecabrini Oct 8, 2025
98512b0
Merge pull request #2 from gabrielecabrini/main
vvzvlad Oct 14, 2025
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12 changes: 12 additions & 0 deletions internal/config/options.go
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Original file line number Diff line number Diff line change
Expand Up @@ -504,6 +504,14 @@ func NewConfigOptions() *configOptions {
return validateChoices(rawValue, []string{"round_robin", "entry_frequency"})
},
},
"POLLING_JITTER": {
ParsedDuration: 10 * time.Minute,
RawValue: "10",
ValueType: minuteType,
Validator: func(rawValue string) error {
return validateGreaterOrEqualThan(rawValue, 1)
},
},
"PORT": {
ParsedStringValue: "",
RawValue: "",
Expand Down Expand Up @@ -902,6 +910,10 @@ func (c *configOptions) PollingScheduler() string {
return c.options["POLLING_SCHEDULER"].ParsedStringValue
}

func (c *configOptions) PollingJitter() time.Duration {
return c.options["POLLING_JITTER"].ParsedDuration
}

func (c *configOptions) Port() string {
return c.options["PORT"].ParsedStringValue
}
Expand Down
15 changes: 15 additions & 0 deletions internal/model/feed.go
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ package model // import "miniflux.app/v2/internal/model"
import (
"fmt"
"io"
"math/rand"
"time"

"miniflux.app/v2/internal/config"
Expand Down Expand Up @@ -143,6 +144,20 @@ func (f *Feed) ScheduleNextCheck(weeklyCount int, refreshDelay time.Duration) ti
interval = min(interval, config.Opts.SchedulerEntryFrequencyMaxInterval())
}

// Apply a small random jitter to spread next checks and reduce thundering herds.
jitterMax := config.Opts.PollingJitter()

randomJitter := time.Duration(rand.Int63n(int64(jitterMax + 1)))
interval += randomJitter

// Re-apply max clamping after randomJitter to avoid exceeding configured caps.
switch config.Opts.PollingScheduler() {
case SchedulerRoundRobin:
interval = min(interval, config.Opts.SchedulerRoundRobinMaxInterval())
case SchedulerEntryFrequency:
interval = min(interval, config.Opts.SchedulerEntryFrequencyMaxInterval())
}

f.NextCheckAt = time.Now().Add(interval)
return interval
}
Expand Down
15 changes: 9 additions & 6 deletions internal/model/feed_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -68,12 +68,15 @@ func TestFeedCheckedNow(t *testing.T) {
}

func checkTargetInterval(t *testing.T, feed *Feed, targetInterval time.Duration, timeBefore time.Time, message string) {
if feed.NextCheckAt.Before(timeBefore.Add(targetInterval)) {
t.Errorf(`The next_check_at should be after timeBefore + %s`, message)
}
if feed.NextCheckAt.After(time.Now().Add(targetInterval)) {
t.Errorf(`The next_check_at should be before now + %s`, message)
}
// Allow a positive jitter up to 10 minutes added by the scheduler.
jitterMax := 10 * time.Minute

if feed.NextCheckAt.Before(timeBefore.Add(targetInterval)) {
t.Errorf(`The next_check_at should be after timeBefore + %s`, message)
}
if feed.NextCheckAt.After(time.Now().Add(targetInterval + jitterMax)) {
t.Errorf(`The next_check_at should be before now + %s (with jitter)`, message)
}
}

func TestFeedScheduleNextCheckRoundRobinDefault(t *testing.T) {
Expand Down