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sampler: Support thereafter of zero (#1033)
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The Zap sampling logger accepts three configuration parameters:
interval, first, and thereafter.

After we see `first` log with the same message in `interval`,
the sampler kicks in.
Following that, we let through every `thereafter`-th log.

So for example,

    NewSamplerWithOptions(core, time.Second, 100, 50)

This will allow 100 logs with the same message in a second,
and following that, every 50th message with that message.

In #1032, the user wanted the sampler to reject *all* duplicate messages
once the limit was reached, but our sampler panics
if `thereafter = 0`.

This change adds support for setting `thereafter` to 0,
dropping all messages in that interval once the limit is reached.
It also adds further explanation to the documentation to address the
misuse in #1032.

Resolves #1032
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abhinav authored Dec 8, 2021
1 parent 10b1fe4 commit 9367581
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Showing 2 changed files with 52 additions and 2 deletions.
15 changes: 13 additions & 2 deletions zapcore/sampler.go
Original file line number Diff line number Diff line change
Expand Up @@ -133,10 +133,21 @@ func SamplerHook(hook func(entry Entry, dec SamplingDecision)) SamplerOption {
// each tick. If more Entries with the same level and message are seen during
// the same interval, every Mth message is logged and the rest are dropped.
//
// For example,
//
// core = NewSamplerWithOptions(core, time.Second, 10, 5)
//
// This will log the first 10 log entries with the same level and message
// in a one second interval as-is. Following that, it will allow through
// every 5th log entry with the same level and message in that interval.
//
// If thereafter is zero, the Core will drop all log entries after the first N
// in that interval.
//
// Sampler can be configured to report sampling decisions with the SamplerHook
// option.
//
// Keep in mind that zap's sampling implementation is optimized for speed over
// Keep in mind that Zap's sampling implementation is optimized for speed over
// absolute precision; under load, each tick may be slightly over- or
// under-sampled.
func NewSamplerWithOptions(core Core, tick time.Duration, first, thereafter int, opts ...SamplerOption) Core {
Expand Down Expand Up @@ -200,7 +211,7 @@ func (s *sampler) Check(ent Entry, ce *CheckedEntry) *CheckedEntry {
if ent.Level >= _minLevel && ent.Level <= _maxLevel {
counter := s.counts.get(ent.Level, ent.Message)
n := counter.IncCheckReset(ent.Time, s.tick)
if n > s.first && (n-s.first)%s.thereafter != 0 {
if n > s.first && (s.thereafter == 0 || (n-s.first)%s.thereafter != 0) {
s.hook(ent, LogDropped)
return ce
}
Expand Down
39 changes: 39 additions & 0 deletions zapcore/sampler_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -275,3 +275,42 @@ func TestSamplerUnknownLevels(t *testing.T) {
})
}
}

func TestSamplerWithZeroThereafter(t *testing.T) {
var counter countingCore

// Logs two messages per second.
sampler := NewSamplerWithOptions(&counter, time.Second, 2, 0)

now := time.Now()

for i := 0; i < 1000; i++ {
ent := Entry{
Level: InfoLevel,
Message: "msg",
Time: now,
}
if ce := sampler.Check(ent, nil); ce != nil {
ce.Write()
}
}

assert.Equal(t, 2, int(counter.logs.Load()),
"Unexpected number of logs")

now = now.Add(time.Second)

for i := 0; i < 1000; i++ {
ent := Entry{
Level: InfoLevel,
Message: "msg",
Time: now,
}
if ce := sampler.Check(ent, nil); ce != nil {
ce.Write()
}
}

assert.Equal(t, 4, int(counter.logs.Load()),
"Unexpected number of logs")
}

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