minio/cmd/crypto/retry.go at dev · dominiklessel/minio

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// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

// http://www.apache.org/licenses/LICENSE-2.0

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

package crypto

import (

"math/rand"

"time"

)

// default retry configuration

const (

retryWaitMin = 100 * time.Millisecond // minimum retry limit.

retryWaitMax = 1500 * time.Millisecond // 1.5 secs worth of max retry.

)

// LinearJitterBackoff provides the time.Duration for a caller to

// perform linear backoff based on the attempt number and with jitter to

// prevent a thundering herd.

// min and max here are *not* absolute values. The number to be multiplied by

// the attempt number will be chosen at random from between them, thus they are

// bounding the jitter.

// For instance:

// * To get strictly linear backoff of one second increasing each retry, set

// both to one second (1s, 2s, 3s, 4s, ...)

// * To get a small amount of jitter centered around one second increasing each

// retry, set to around one second, such as a min of 800ms and max of 1200ms

// (892ms, 2102ms, 2945ms, 4312ms, ...)

// * To get extreme jitter, set to a very wide spread, such as a min of 100ms

// and a max of 20s (15382ms, 292ms, 51321ms, 35234ms, ...)

func LinearJitterBackoff(min, max time.Duration, attemptNum int) time.Duration {

// attemptNum always starts at zero but we want to start at 1 for multiplication

attemptNum++

if max <= min {

// Unclear what to do here, or they are the same, so return min *

// attemptNum

return min * time.Duration(attemptNum)

}

// Seed rand; doing this every time is fine

rand := rand.New(rand.NewSource(int64(time.Now().Nanosecond())))

// Pick a random number that lies somewhere between the min and max and

// multiply by the attemptNum. attemptNum starts at zero so we always

// increment here. We first get a random percentage, then apply that to the

// difference between min and max, and add to min.

jitter := rand.Float64() * float64(max-min)

jitterMin := int64(jitter) + int64(min)

return time.Duration(jitterMin * int64(attemptNum))

}

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