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66 lines
2.5 KiB
66 lines
2.5 KiB
5 years ago
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// MinIO Cloud Storage, (C) 2020 MinIO, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package crypto
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import (
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"math/rand"
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"time"
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)
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// default retry configuration
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const (
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retryWaitMin = 500 * time.Millisecond // minimum retry limit.
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retryWaitMax = 3 * time.Second // 3 secs worth of max retry.
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retryMax = 2
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)
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// LinearJitterBackoff provides the time.Duration for a caller to
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// perform linear backoff based on the attempt number and with jitter to
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// prevent a thundering herd.
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//
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// min and max here are *not* absolute values. The number to be multiplied by
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// the attempt number will be chosen at random from between them, thus they are
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// bounding the jitter.
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//
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// For instance:
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// * To get strictly linear backoff of one second increasing each retry, set
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// both to one second (1s, 2s, 3s, 4s, ...)
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// * To get a small amount of jitter centered around one second increasing each
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// retry, set to around one second, such as a min of 800ms and max of 1200ms
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// (892ms, 2102ms, 2945ms, 4312ms, ...)
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// * To get extreme jitter, set to a very wide spread, such as a min of 100ms
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// and a max of 20s (15382ms, 292ms, 51321ms, 35234ms, ...)
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func LinearJitterBackoff(min, max time.Duration, attemptNum int) time.Duration {
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// attemptNum always starts at zero but we want to start at 1 for multiplication
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attemptNum++
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if max <= min {
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// Unclear what to do here, or they are the same, so return min *
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// attemptNum
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return min * time.Duration(attemptNum)
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}
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// Seed rand; doing this every time is fine
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rand := rand.New(rand.NewSource(int64(time.Now().Nanosecond())))
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// Pick a random number that lies somewhere between the min and max and
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// multiply by the attemptNum. attemptNum starts at zero so we always
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// increment here. We first get a random percentage, then apply that to the
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// difference between min and max, and add to min.
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jitter := rand.Float64() * float64(max-min)
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jitterMin := int64(jitter) + int64(min)
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return time.Duration(jitterMin * int64(attemptNum))
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}
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