minio/cmd/crypto/retry.go

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// MinIO Cloud Storage, (C) 2020 MinIO, Inc.
//
// 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 = 500 * time.Millisecond // minimum retry limit.
retryWaitMax = 3 * time.Second // 3 secs worth of max retry.
retryMax = 2
)
// 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))
}