mirror of https://github.com/octoleo/restic.git
99 lines
3.0 KiB
Go
99 lines
3.0 KiB
Go
package backup
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import (
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"container/list"
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"time"
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)
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// rateBucket represents a one second window of recorded progress.
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type rateBucket struct {
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totalBytes uint64
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end time.Time // the end of the time window, exclusive
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}
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// rateEstimator represents an estimate of the time to complete an operation.
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type rateEstimator struct {
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buckets *list.List
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start time.Time
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totalBytes uint64
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}
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// newRateEstimator returns an estimator initialized to a presumed start time.
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func newRateEstimator(start time.Time) *rateEstimator {
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return &rateEstimator{buckets: list.New(), start: start}
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}
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// See trim(), below.
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const (
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bucketWidth = time.Second
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minRateEstimatorBytes = 100 * 1000 * 1000
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minRateEstimatorBuckets = 20
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minRateEstimatorMinutes = 2
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)
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// trim removes the oldest history from the estimator assuming a given
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// current time.
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func (r *rateEstimator) trim(now time.Time) {
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// The estimator retains byte transfer counts over a two minute window.
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// However, to avoid removing too much history when transfer rates are
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// low, the estimator also retains a minimum number of processed bytes
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// across a minimum number of buckets. An operation that is processing a
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// significant number of bytes per second will typically retain only a
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// two minute window's worth of information. One that is making slow
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// progress, such as one being over a rate limited connection, typically
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// observes bursts of updates as infrequently as every ten or twenty
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// seconds, in which case the other limiters will kick in. This heuristic
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// avoids wildly fluctuating estimates over rate limited connections.
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start := now.Add(-minRateEstimatorMinutes * time.Minute)
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for e := r.buckets.Front(); e != nil; e = r.buckets.Front() {
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if r.buckets.Len() <= minRateEstimatorBuckets {
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break
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}
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b := e.Value.(*rateBucket)
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if b.end.After(start) {
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break
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}
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total := r.totalBytes - b.totalBytes
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if total < minRateEstimatorBytes {
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break
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}
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r.start = b.end
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r.totalBytes = total
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r.buckets.Remove(e)
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}
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}
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// recordBytes records the transfer of a number of bytes at a given
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// time. Times passed in successive calls should advance monotonically (as
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// is the case with time.Now().
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func (r *rateEstimator) recordBytes(now time.Time, bytes uint64) {
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if bytes == 0 {
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return
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}
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var tail *rateBucket
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if r.buckets.Len() > 0 {
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tail = r.buckets.Back().Value.(*rateBucket)
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}
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if tail == nil || !tail.end.After(now) {
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// The new bucket holds measurements in the time range [now .. now+1sec).
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tail = &rateBucket{end: now.Add(bucketWidth)}
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r.buckets.PushBack(tail)
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}
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tail.totalBytes += bytes
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r.totalBytes += bytes
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r.trim(now)
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}
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// rate returns an estimated bytes per second rate at a given time, or zero
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// if there is not enough data to compute a rate.
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func (r *rateEstimator) rate(now time.Time) float64 {
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r.trim(now)
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if !r.start.Before(now) {
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return 0
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}
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elapsed := float64(now.Sub(r.start)) / float64(time.Second)
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rate := float64(r.totalBytes) / elapsed
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return rate
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}
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