forked from cockroachdb/cockroach
/
replica_stats.go
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/
replica_stats.go
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// Copyright 2017 The Cockroach Authors.
//
// 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 storage
import (
"math"
"time"
"github.com/cockroachdb/cockroach/pkg/roachpb"
"github.com/cockroachdb/cockroach/pkg/util/hlc"
"github.com/cockroachdb/cockroach/pkg/util/syncutil"
)
const (
replStatsRotateInterval = 5 * time.Minute
decayFactor = 0.8
)
type localityOracle func(roachpb.NodeID) string
// perLocalityCounts maps from the string representation of a locality to count.
type perLocalityCounts map[string]float64
// replicaStats maintains statistics about the work done by a replica. Its
// initial use is tracking the number of requests received from each
// cluster locality in order to inform lease transfer decisions.
type replicaStats struct {
clock *hlc.Clock
getNodeLocality localityOracle
// We use a set of time windows in order to age out old stats without having
// to do hard resets. The `requests` array is a circular buffer of the last
// N windows of stats. We rotate through the circular buffer every so often
// as determined by `replStatsRotateInterval`.
//
// We could alternatively use a forward decay approach here, but it would
// require more memory than this slightly less precise windowing method:
// http://dimacs.rutgers.edu/~graham/pubs/papers/fwddecay.pdf
mu struct {
syncutil.Mutex
idx int
requests [6]perLocalityCounts
lastRotate time.Time
lastReset time.Time
}
}
func newReplicaStats(clock *hlc.Clock, getNodeLocality localityOracle) *replicaStats {
rs := &replicaStats{
clock: clock,
getNodeLocality: getNodeLocality,
}
rs.mu.requests[rs.mu.idx] = make(perLocalityCounts)
rs.mu.lastRotate = time.Unix(0, rs.clock.PhysicalNow())
rs.mu.lastReset = rs.mu.lastRotate
return rs
}
func (rs *replicaStats) record(nodeID roachpb.NodeID) {
rs.recordCount(1, nodeID)
}
func (rs *replicaStats) recordCount(count float64, nodeID roachpb.NodeID) {
var locality string
if rs.getNodeLocality != nil {
locality = rs.getNodeLocality(nodeID)
}
now := time.Unix(0, rs.clock.PhysicalNow())
rs.mu.Lock()
defer rs.mu.Unlock()
rs.maybeRotateLocked(now)
rs.mu.requests[rs.mu.idx][locality] += count
}
func (rs *replicaStats) maybeRotateLocked(now time.Time) {
if now.Sub(rs.mu.lastRotate) >= replStatsRotateInterval {
rs.rotateLocked()
rs.mu.lastRotate = now
}
}
func (rs *replicaStats) rotateLocked() {
rs.mu.idx = (rs.mu.idx + 1) % len(rs.mu.requests)
rs.mu.requests[rs.mu.idx] = make(perLocalityCounts)
}
// perLocalityDecayingQPS returns the per-locality QPS and the amount of time
// over which the stats were accumulated.
// Note that the QPS stats are exponentially decayed such that newer requests
// are weighted more heavily than older requests.
func (rs *replicaStats) perLocalityDecayingQPS() (perLocalityCounts, time.Duration) {
now := time.Unix(0, rs.clock.PhysicalNow())
rs.mu.Lock()
defer rs.mu.Unlock()
rs.maybeRotateLocked(now)
// Use the fraction of time since the last rotation as a smoothing factor to
// avoid jarring changes in request count immediately before/after a rotation.
timeSinceRotate := now.Sub(rs.mu.lastRotate)
fractionOfRotation := float64(timeSinceRotate) / float64(replStatsRotateInterval)
counts := make(perLocalityCounts)
var duration time.Duration
for i := range rs.mu.requests {
// We have to add len(rs.mu.requests) to the numerator to avoid getting a
// negative result from the modulus operation when rs.mu.idx is small.
requestsIdx := (rs.mu.idx + len(rs.mu.requests) - i) % len(rs.mu.requests)
if cur := rs.mu.requests[requestsIdx]; cur != nil {
decay := math.Pow(decayFactor, float64(i)+fractionOfRotation)
if i == 0 {
duration += time.Duration(float64(timeSinceRotate) * decay)
} else {
duration += time.Duration(float64(replStatsRotateInterval) * decay)
}
for k, v := range cur {
counts[k] += v * decay
}
}
}
if duration.Seconds() > 0 {
for k := range counts {
counts[k] = counts[k] / duration.Seconds()
}
}
return counts, now.Sub(rs.mu.lastReset)
}
// avgQPS returns the average requests-per-second and the amount of time
// over which the stat was accumulated. Note that these averages are exact,
// not exponentially decayed (there isn't a ton of justification for going
// one way or the the other, but not decaying makes the average more stable,
// which is probably better for avoiding rebalance thrashing).
func (rs *replicaStats) avgQPS() (float64, time.Duration) {
now := time.Unix(0, rs.clock.PhysicalNow())
rs.mu.Lock()
defer rs.mu.Unlock()
rs.maybeRotateLocked(now)
// First accumulate the counts, then divide by the total number of seconds.
var sum float64
var windowsUsed int
for i := range rs.mu.requests {
// We have to add len(rs.mu.requests) to the numerator to avoid getting a
// negative result from the modulus operation when rs.mu.idx is small.
requestsIdx := (rs.mu.idx + len(rs.mu.requests) - i) % len(rs.mu.requests)
if cur := rs.mu.requests[requestsIdx]; cur != nil {
windowsUsed++
for _, v := range cur {
sum += v
}
}
}
if windowsUsed <= 0 {
return 0, 0
}
duration := now.Sub(rs.mu.lastRotate) + time.Duration(windowsUsed-1)*replStatsRotateInterval
if duration == 0 {
return 0, 0
}
return sum / duration.Seconds(), duration
}
func (rs *replicaStats) resetRequestCounts() {
rs.mu.Lock()
defer rs.mu.Unlock()
for i := range rs.mu.requests {
rs.mu.requests[i] = nil
}
rs.mu.requests[rs.mu.idx] = make(perLocalityCounts)
rs.mu.lastRotate = time.Unix(0, rs.clock.PhysicalNow())
rs.mu.lastReset = rs.mu.lastRotate
}