This repository has been archived by the owner on May 26, 2022. It is now read-only.
-
Notifications
You must be signed in to change notification settings - Fork 13
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
added initial backoff cache discovery
- Loading branch information
1 parent
d248d63
commit 393cf50
Showing
5 changed files
with
861 additions
and
0 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,181 @@ | ||
package discovery | ||
|
||
import ( | ||
"math" | ||
"math/rand" | ||
"time" | ||
) | ||
|
||
type BackoffFactory func() BackoffStrategy | ||
|
||
type BackoffStrategy interface { | ||
Delay() time.Duration | ||
Reset() | ||
} | ||
|
||
// Jitter implementations taken roughly from https://aws.amazon.com/blogs/architecture/exponential-backoff-and-jitter/ | ||
|
||
// Jitter must return a duration between min and max. Min must be lower than, or equal to, max. | ||
type Jitter func(duration time.Duration, min time.Duration, max time.Duration, rng *rand.Rand) time.Duration | ||
|
||
func FullJitter(duration time.Duration, min time.Duration, max time.Duration, rng *rand.Rand) time.Duration { | ||
if duration <= min { | ||
return min | ||
} | ||
|
||
normalizedDur := boundedDuration(duration, min, max) - min | ||
|
||
return boundedDuration(time.Duration(rng.Int63n(int64(normalizedDur)))+min, min, max) | ||
} | ||
|
||
func NoJitter(duration time.Duration, min time.Duration, max time.Duration, rng *rand.Rand) time.Duration { | ||
return boundedDuration(duration, min, max) | ||
} | ||
|
||
type randomizedBackoff struct { | ||
min time.Duration | ||
max time.Duration | ||
rng *rand.Rand | ||
} | ||
|
||
func (b *randomizedBackoff) BoundedDelay(duration time.Duration) time.Duration { | ||
return boundedDuration(duration, b.min, b.max) | ||
} | ||
|
||
func boundedDuration(d time.Duration, min time.Duration, max time.Duration) time.Duration { | ||
if d < min { | ||
return min | ||
} | ||
if d > max { | ||
return max | ||
} | ||
return d | ||
} | ||
|
||
type attemptBackoff struct { | ||
attempt int | ||
jitter Jitter | ||
randomizedBackoff | ||
} | ||
|
||
func (b *attemptBackoff) Reset() { | ||
b.attempt = 0 | ||
} | ||
|
||
func NewFixedBackoffFactory(delay time.Duration) BackoffFactory { | ||
return func() BackoffStrategy { | ||
return &fixedBackoff{delay: delay} | ||
} | ||
} | ||
|
||
type fixedBackoff struct { | ||
delay time.Duration | ||
} | ||
|
||
func (b *fixedBackoff) Delay() time.Duration { | ||
return b.delay | ||
} | ||
|
||
func (b *fixedBackoff) Reset() {} | ||
|
||
func NewPolynomialBackoffFactory(min, max time.Duration, jitter Jitter, | ||
timeUnits time.Duration, polyCoefs []float64, rng *rand.Rand) BackoffFactory { | ||
return func() BackoffStrategy { | ||
return &polynomialBackoff{ | ||
attemptBackoff: attemptBackoff{ | ||
randomizedBackoff: randomizedBackoff{ | ||
min: min, | ||
max: max, | ||
rng: rng, | ||
}, | ||
jitter: jitter, | ||
}, | ||
timeUnits: timeUnits, | ||
poly: polyCoefs, | ||
} | ||
} | ||
} | ||
|
||
type polynomialBackoff struct { | ||
attemptBackoff | ||
timeUnits time.Duration | ||
poly []float64 | ||
} | ||
|
||
func (b *polynomialBackoff) Delay() time.Duration { | ||
polySum := b.poly[0] | ||
exp := 1 | ||
attempt := b.attempt | ||
b.attempt++ | ||
|
||
for _, c := range b.poly[1:] { | ||
exp *= attempt | ||
polySum += float64(exp) * c | ||
} | ||
return b.jitter(time.Duration(float64(b.timeUnits)*polySum), b.min, b.max, b.rng) | ||
} | ||
|
||
func NewExponentialBackoffFactory(min, max time.Duration, jitter Jitter, | ||
timeUnits time.Duration, base float64, offset time.Duration, rng *rand.Rand) BackoffFactory { | ||
return func() BackoffStrategy { | ||
return &exponentialBackoff{ | ||
attemptBackoff: attemptBackoff{ | ||
randomizedBackoff: randomizedBackoff{ | ||
min: min, | ||
max: max, | ||
rng: rng, | ||
}, | ||
jitter: jitter, | ||
}, | ||
timeUnits: timeUnits, | ||
base: base, | ||
offset: offset, | ||
} | ||
} | ||
} | ||
|
||
type exponentialBackoff struct { | ||
attemptBackoff | ||
timeUnits time.Duration | ||
base float64 | ||
offset time.Duration | ||
} | ||
|
||
func (b *exponentialBackoff) Delay() time.Duration { | ||
attempt := b.attempt | ||
b.attempt++ | ||
return b.jitter( | ||
time.Duration(math.Pow(b.base, float64(attempt))*float64(b.timeUnits))+b.offset, b.min, b.max, b.rng) | ||
} | ||
|
||
func NewExponentialDecorrelatedJitterFactory(min, max time.Duration, base float64, rng *rand.Rand) BackoffFactory { | ||
return func() BackoffStrategy { | ||
return &exponentialDecorrelatedJitter{ | ||
randomizedBackoff: randomizedBackoff{ | ||
min: min, | ||
max: max, | ||
rng: rng, | ||
}, | ||
base: base, | ||
} | ||
} | ||
} | ||
|
||
type exponentialDecorrelatedJitter struct { | ||
randomizedBackoff | ||
base float64 | ||
lastDelay time.Duration | ||
} | ||
|
||
func (b *exponentialDecorrelatedJitter) Delay() time.Duration { | ||
if b.lastDelay < b.min { | ||
b.lastDelay = b.min | ||
return b.lastDelay | ||
} | ||
|
||
nextMax := int64(float64(b.lastDelay) * b.base) | ||
b.lastDelay = boundedDuration(time.Duration(b.rng.Int63n(nextMax-int64(b.min)))+b.min, b.min, b.max) | ||
return b.lastDelay | ||
} | ||
|
||
func (b *exponentialDecorrelatedJitter) Reset() { b.lastDelay = 0 } |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,125 @@ | ||
package discovery | ||
|
||
import ( | ||
"math/rand" | ||
"testing" | ||
"time" | ||
) | ||
|
||
func checkDelay(bkf BackoffStrategy, expected time.Duration, t *testing.T) { | ||
t.Helper() | ||
if calculated := bkf.Delay(); calculated != expected { | ||
t.Fatalf("expected %v, got %v", expected, calculated) | ||
} | ||
} | ||
|
||
func TestFixedBackoff(t *testing.T) { | ||
startDelay := time.Second | ||
delay := startDelay | ||
|
||
bkf := NewFixedBackoffFactory(delay) | ||
delay *= 2 | ||
b1 := bkf() | ||
delay *= 2 | ||
b2 := bkf() | ||
|
||
if b1.Delay() != startDelay || b2.Delay() != startDelay { | ||
t.Fatal("incorrect delay time") | ||
} | ||
|
||
if b1.Delay() != startDelay { | ||
t.Fatal("backoff is stateful") | ||
} | ||
|
||
if b1.Reset(); b1.Delay() != startDelay { | ||
t.Fatalf("Reset does something") | ||
} | ||
} | ||
|
||
func TestPolynomialBackoff(t *testing.T) { | ||
rng := rand.New(rand.NewSource(0)) | ||
bkf := NewPolynomialBackoffFactory(time.Second, time.Second*33, NoJitter, time.Second, []float64{0.5, 2, 3}, rng) | ||
b1 := bkf() | ||
b2 := bkf() | ||
|
||
if b1.Delay() != time.Second || b2.Delay() != time.Second { | ||
t.Fatal("incorrect delay time") | ||
} | ||
|
||
checkDelay(b1, time.Millisecond*5500, t) | ||
checkDelay(b1, time.Millisecond*16500, t) | ||
checkDelay(b1, time.Millisecond*33000, t) | ||
checkDelay(b2, time.Millisecond*5500, t) | ||
|
||
b1.Reset() | ||
b1.Delay() | ||
checkDelay(b1, time.Millisecond*5500, t) | ||
} | ||
|
||
func TestExponentialBackoff(t *testing.T) { | ||
rng := rand.New(rand.NewSource(0)) | ||
bkf := NewExponentialBackoffFactory(time.Millisecond*650, time.Second*7, NoJitter, time.Second, 1.5, -time.Millisecond*400, rng) | ||
b1 := bkf() | ||
b2 := bkf() | ||
|
||
if b1.Delay() != time.Millisecond*650 || b2.Delay() != time.Millisecond*650 { | ||
t.Fatal("incorrect delay time") | ||
} | ||
|
||
checkDelay(b1, time.Millisecond*1100, t) | ||
checkDelay(b1, time.Millisecond*1850, t) | ||
checkDelay(b1, time.Millisecond*2975, t) | ||
checkDelay(b1, time.Microsecond*4662500, t) | ||
checkDelay(b1, time.Second*7, t) | ||
checkDelay(b2, time.Millisecond*1100, t) | ||
|
||
b1.Reset() | ||
b1.Delay() | ||
checkDelay(b1, time.Millisecond*1100, t) | ||
} | ||
|
||
func minMaxJitterTest(jitter Jitter, t *testing.T) { | ||
rng := rand.New(rand.NewSource(0)) | ||
if jitter(time.Nanosecond, time.Hour*10, time.Hour*20, rng) < time.Hour*10 { | ||
t.Fatal("Min not working") | ||
} | ||
if jitter(time.Hour, time.Nanosecond, time.Nanosecond*10, rng) > time.Nanosecond*10 { | ||
t.Fatal("Max not working") | ||
} | ||
} | ||
|
||
func TestNoJitter(t *testing.T) { | ||
minMaxJitterTest(NoJitter, t) | ||
for i := 0; i < 10; i++ { | ||
expected := time.Second * time.Duration(i) | ||
if calculated := NoJitter(expected, time.Duration(0), time.Second*100, nil); calculated != expected { | ||
t.Fatalf("expected %v, got %v", expected, calculated) | ||
} | ||
} | ||
} | ||
|
||
func TestFullJitter(t *testing.T) { | ||
rng := rand.New(rand.NewSource(0)) | ||
minMaxJitterTest(FullJitter, t) | ||
const numBuckets = 51 | ||
const multiplier = 10 | ||
const threshold = 20 | ||
|
||
histogram := make([]int, numBuckets) | ||
|
||
for i := 0; i < (numBuckets-1)*multiplier; i++ { | ||
started := time.Nanosecond * 50 | ||
calculated := FullJitter(started, 0, 100, rng) | ||
histogram[calculated]++ | ||
} | ||
|
||
for _, count := range histogram { | ||
if count > threshold { | ||
t.Fatal("jitter is not close to evenly spread") | ||
} | ||
} | ||
|
||
if histogram[numBuckets-1] > 0 { | ||
t.Fatal("jitter increased overall time") | ||
} | ||
} |
Oops, something went wrong.