etcdserver/api/v3compactor/periodic.go
func (pc *Periodic) Run() {
	compactInterval := pc.getCompactInterval()
	retryInterval := pc.getRetryInterval()
	retentions := pc.getRetentions()

	go func() {
		lastSuccess := pc.clock.Now()
		baseInterval := pc.period
		for {
			pc.revs = append(pc.revs, pc.rg.Rev())
			if len(pc.revs) > retentions {
				pc.revs = pc.revs[1:] // pc.revs[0] is always the rev at pc.period ago
			}

			select {
			case <-pc.ctx.Done():
				return
			case <-pc.clock.After(retryInterval):
				pc.mu.Lock()
				p := pc.paused
				pc.mu.Unlock()
				if p {
					continue
				}
			}

			if pc.clock.Now().Sub(lastSuccess) < baseInterval {
				continue
			}

			// wait up to initial given period
			if baseInterval == pc.period {
				baseInterval = compactInterval
			}
			rev := pc.revs[0]

			if pc.lg != nil {
				pc.lg.Info(
					"starting auto periodic compaction",
					zap.Int64("revision", rev),
					zap.Duration("compact-period", pc.period),
				)
			} else {
				plog.Noticef("Starting auto-compaction at revision %d (retention: %v)", rev, pc.period)
			}
			_, err := pc.c.Compact(pc.ctx, &pb.CompactionRequest{Revision: rev})
			if err == nil || err == mvcc.ErrCompacted {
				if pc.lg != nil {
					pc.lg.Info(
						"completed auto periodic compaction",
						zap.Int64("revision", rev),
						zap.Duration("compact-period", pc.period),
						zap.Duration("took", time.Since(lastSuccess)),
					)
				} else {
					plog.Noticef("Finished auto-compaction at revision %d", rev)
				}
				lastSuccess = pc.clock.Now()
			} else {
				if pc.lg != nil {
					pc.lg.Warn(
						"failed auto periodic compaction",
						zap.Int64("revision", rev),
						zap.Duration("compact-period", pc.period),
						zap.Duration("retry-interval", retryInterval),
						zap.Error(err),
					)
				} else {
					plog.Noticef("Failed auto-compaction at revision %d (%v)", rev, err)
					plog.Noticef("Retry after %v", retryInterval)
				}
			}
		}
	}()
}
func (pc *Periodic) Run() {
	compactInterval := pc.getCompactInterval()
	retryInterval := pc.getRetryInterval()
	retentions := pc.getRetentions()

	go func() {
		lastSuccess := pc.clock.Now()
		baseInterval := pc.period
		for {
			pc.revs = append(pc.revs, pc.rg.Rev())
			if len(pc.revs) > retentions {
				pc.revs = pc.revs[1:] // pc.revs[0] is always the rev at pc.period ago
			}

			select {
			case <-pc.ctx.Done():
				return
			case <-pc.clock.After(retryInterval):
				pc.mu.Lock()
				p := pc.paused
				pc.mu.Unlock()
				if p {
					continue
				}
			}

			if pc.clock.Now().Sub(lastSuccess) < baseInterval {
				continue
			}

			// wait up to initial given period
			if baseInterval == pc.period {
				baseInterval = compactInterval
			}
			rev := pc.revs[0]

			if pc.lg != nil {
				pc.lg.Info(
					"starting auto periodic compaction",
					zap.Int64("revision", rev),
					zap.Duration("compact-period", pc.period),
				)
			} else {
				plog.Noticef("Starting auto-compaction at revision %d (retention: %v)", rev, pc.period)
			}
			_, err := pc.c.Compact(pc.ctx, &pb.CompactionRequest{Revision: rev})
			if err == nil || err == mvcc.ErrCompacted {
				if pc.lg != nil {
					pc.lg.Info(
						"completed auto periodic compaction",
						zap.Int64("revision", rev),
						zap.Duration("compact-period", pc.period),
						zap.Duration("took", time.Since(lastSuccess)),
					)
				} else {
					plog.Noticef("Finished auto-compaction at revision %d", rev)
				}
				lastSuccess = pc.clock.Now()
			} else {
				if pc.lg != nil {
					pc.lg.Warn(
						"failed auto periodic compaction",
						zap.Int64("revision", rev),
						zap.Duration("compact-period", pc.period),
						zap.Duration("retry-interval", retryInterval),
						zap.Error(err),
					)
				} else {
					plog.Noticef("Failed auto-compaction at revision %d (%v)", rev, err)
					plog.Noticef("Retry after %v", retryInterval)
				}
			}
		}
	}()
}
/*
Compaction period 1-hour:
  1. compute compaction period, which is 1-hour
  2. record revisions for every 1/10 of 1-hour (6-minute)
  3. keep recording revisions with no compaction for first 1-hour
  4. do compact with revs[0]
	- success? contiue on for-loop and move sliding window; revs = revs[1:]
	- failure? update revs, and retry after 1/10 of 1-hour (6-minute)

Compaction period 24-hour:
  1. compute compaction period, which is 1-hour
  2. record revisions for every 1/10 of 1-hour (6-minute)
  3. keep recording revisions with no compaction for first 24-hour
  4. do compact with revs[0]
	- success? contiue on for-loop and move sliding window; revs = revs[1:]
	- failure? update revs, and retry after 1/10 of 1-hour (6-minute)

Compaction period 59-min:
  1. compute compaction period, which is 59-min
  2. record revisions for every 1/10 of 59-min (5.9-min)
  3. keep recording revisions with no compaction for first 59-min
  4. do compact with revs[0]
	- success? contiue on for-loop and move sliding window; revs = revs[1:]
	- failure? update revs, and retry after 1/10 of 59-min (5.9-min)

Compaction period 5-sec:
  1. compute compaction period, which is 5-sec
  2. record revisions for every 1/10 of 5-sec (0.5-sec)
  3. keep recording revisions with no compaction for first 5-sec
  4. do compact with revs[0]
	- success? contiue on for-loop and move sliding window; revs = revs[1:]
	- failure? update revs, and retry after 1/10 of 5-sec (0.5-sec)
*/
// Run runs periodic compactor.