From 8b7944cba66e4cbc126238d3cd62b738d58775e4 Mon Sep 17 00:00:00 2001 From: Tobias Grieger Date: Mon, 9 May 2022 14:13:44 +0200 Subject: [PATCH] metric: add prometheus-based histogram Our current histogram is based on `hdrhistogram`. This tends to create lots of buckets and is inflexible w.r.t the bucket layout. In hindsight, it was a poor choice of default implementation (I can say that since I introduced it) and its cost is disincentivizing the introduction of histograms that would be useful. This commit introduces a histogram that is based on a completely vanilla `prometheus.Histogram`. The only reason we need to wrap it is because we want to export quantiles to CockraochDB's internal timeseries (it does not support histograms) and this requires maintaining an internal windowed histogram (on top of the cumulative histogram). With this done, we can now introduce metrics with any kind of buckets we want. Helpfully, we introduce two common kinds of buckets, suitable for IO-type and RPC-type latencies. These are defined in a human-readable format by explicitly listing out the buckets. We can move existing metrics to HistogramV2 easily, assuming we are not concerned with existing prometheus scrapers getting tripped up by the changes in bucket boundaries. I assume this is not a big deal in practice as long as it doesn't happen "all the time". In fact, I would strongly suggest we move all metrics wholesale and remove the hdrhistogram-based implementation. If this is not acceptable for some reason, we ought to at least deprecated it. We also slightly improve the existing `Histogram` code by unifying how the windowed histograms are ticked and by making explicit where their quantiles are recorded (this dependency was previously hidden via a local interface assertion). Resolves https://github.com/cockroachdb/cockroach/issues/10015. Resolves https://github.com/cockroachdb/cockroach/issues/64962. Alternative to https://github.com/dhartunian/cockroach/commit/eac3d066de2703f75207a2c3b80ac42c4f4074c5 TODO - export quantiles (how to do this? Not clear, don't see the code laying around in prometheus, might have to hand-roll it but should be easy enough) Release note: None --- pkg/kv/kvserver/BUILD.bazel | 1 + pkg/kv/kvserver/metrics.go | 9 +- pkg/kv/kvserver/scheduler.go | 2 +- pkg/server/status/BUILD.bazel | 2 + pkg/server/status/recorder.go | 31 +++-- pkg/util/metric/BUILD.bazel | 2 +- pkg/util/metric/metric.go | 176 +++++++++++++++++++++++++-- pkg/util/metric/metric_test.go | 56 +++++++++ pkg/util/metric/sliding_histogram.go | 61 ---------- pkg/util/metric/tick_helper.go | 34 ++++++ 10 files changed, 291 insertions(+), 83 deletions(-) delete mode 100644 pkg/util/metric/sliding_histogram.go create mode 100644 pkg/util/metric/tick_helper.go diff --git a/pkg/kv/kvserver/BUILD.bazel b/pkg/kv/kvserver/BUILD.bazel index e39af08771b1..2b1e186b3351 100644 --- a/pkg/kv/kvserver/BUILD.bazel +++ b/pkg/kv/kvserver/BUILD.bazel @@ -208,6 +208,7 @@ go_library( "@com_github_gogo_protobuf//proto", "@com_github_google_btree//:btree", "@com_github_kr_pretty//:pretty", + "@com_github_prometheus_client_golang//prometheus", "@io_etcd_go_etcd_raft_v3//:raft", "@io_etcd_go_etcd_raft_v3//raftpb", "@io_etcd_go_etcd_raft_v3//tracker", diff --git a/pkg/kv/kvserver/metrics.go b/pkg/kv/kvserver/metrics.go index b74403f81fcd..42dee585e3e2 100644 --- a/pkg/kv/kvserver/metrics.go +++ b/pkg/kv/kvserver/metrics.go @@ -31,6 +31,7 @@ import ( "github.com/cockroachdb/cockroach/pkg/util/slidingwindow" "github.com/cockroachdb/cockroach/pkg/util/syncutil" "github.com/cockroachdb/cockroach/pkg/util/timeutil" + "github.com/prometheus/client_golang/prometheus" "go.etcd.io/etcd/raft/v3/raftpb" ) @@ -1738,7 +1739,7 @@ type StoreMetrics struct { RaftCommandCommitLatency *metric.Histogram RaftHandleReadyLatency *metric.Histogram RaftApplyCommittedLatency *metric.Histogram - RaftSchedulerLatency *metric.Histogram + RaftSchedulerLatency *metric.HistogramV2 RaftTimeoutCampaign *metric.Counter // Raft message metrics. @@ -2239,8 +2240,10 @@ func newStoreMetrics(histogramWindow time.Duration) *StoreMetrics { RaftCommandCommitLatency: metric.NewLatency(metaRaftCommandCommitLatency, histogramWindow), RaftHandleReadyLatency: metric.NewLatency(metaRaftHandleReadyLatency, histogramWindow), RaftApplyCommittedLatency: metric.NewLatency(metaRaftApplyCommittedLatency, histogramWindow), - RaftSchedulerLatency: metric.NewLatency(metaRaftSchedulerLatency, histogramWindow), - RaftTimeoutCampaign: metric.NewCounter(metaRaftTimeoutCampaign), + RaftSchedulerLatency: metric.NewHistogramV2(metaRaftSchedulerLatency, histogramWindow, prometheus.HistogramOpts{ + Buckets: metric.IOLatencyBuckets, + }), + RaftTimeoutCampaign: metric.NewCounter(metaRaftTimeoutCampaign), // Raft message metrics. RaftRcvdMessages: [...]*metric.Counter{ diff --git a/pkg/kv/kvserver/scheduler.go b/pkg/kv/kvserver/scheduler.go index dbfdddb843d6..2ed446471219 100644 --- a/pkg/kv/kvserver/scheduler.go +++ b/pkg/kv/kvserver/scheduler.go @@ -169,7 +169,7 @@ type raftScheduleState struct { type raftScheduler struct { ambientContext log.AmbientContext processor raftProcessor - latency *metric.Histogram + latency *metric.HistogramV2 numWorkers int mu struct { diff --git a/pkg/server/status/BUILD.bazel b/pkg/server/status/BUILD.bazel index 216b2b0da11d..a4ddbc1fa350 100644 --- a/pkg/server/status/BUILD.bazel +++ b/pkg/server/status/BUILD.bazel @@ -68,6 +68,8 @@ go_library( "@com_github_codahale_hdrhistogram//:hdrhistogram", "@com_github_dustin_go_humanize//:go-humanize", "@com_github_elastic_gosigar//:gosigar", + "@com_github_prometheus_client_golang//prometheus", + "@com_github_prometheus_client_model//go", "@com_github_shirou_gopsutil_v3//net", ] + select({ "@io_bazel_rules_go//go/platform:aix": [ diff --git a/pkg/server/status/recorder.go b/pkg/server/status/recorder.go index 464eaa160eb8..3667b5eb6741 100644 --- a/pkg/server/status/recorder.go +++ b/pkg/server/status/recorder.go @@ -44,9 +44,9 @@ import ( "github.com/cockroachdb/cockroach/pkg/util/system" "github.com/cockroachdb/errors" "github.com/cockroachdb/redact" - "github.com/codahale/hdrhistogram" - humanize "github.com/dustin/go-humanize" + "github.com/dustin/go-humanize" "github.com/elastic/gosigar" + prometheusgo "github.com/prometheus/client_model/go" ) const ( @@ -531,12 +531,10 @@ func extractValue(name string, mtr interface{}, fn func(string, float64)) error // TODO(tschottdorf,ajwerner): consider moving this switch to a single // interface implemented by the individual metric types. type ( - float64Valuer interface{ Value() float64 } - int64Valuer interface{ Value() int64 } - int64Counter interface{ Count() int64 } - histogramValuer interface { - Windowed() (*hdrhistogram.Histogram, time.Duration) - } + float64Valuer interface{ Value() float64 } + int64Valuer interface{ Value() int64 } + int64Counter interface{ Count() int64 } + prometheusMetricValuer interface{ ToPrometheusMetric() *prometheusgo.Metric } ) switch mtr := mtr.(type) { case float64: @@ -547,7 +545,7 @@ func extractValue(name string, mtr interface{}, fn func(string, float64)) error fn(name, float64(mtr.Value())) case int64Counter: fn(name, float64(mtr.Count())) - case histogramValuer: + case *metric.Histogram: // TODO(mrtracy): Where should this comment go for better // visibility? // @@ -567,6 +565,21 @@ func extractValue(name string, mtr interface{}, fn func(string, float64)) error fn(name+pt.suffix, float64(curr.ValueAtQuantile(pt.quantile))) } fn(name+"-count", float64(curr.TotalCount())) + case *metric.HistogramV2: + // NB: this branch is intentionally at the bottom since all metrics implement it. + cur := mtr.Windowed() + var m prometheusgo.Metric + _ = cur.Write(&m) + hist := m.Histogram + n := float64(*hist.SampleCount) + fn(name+"-count", n) + fn(name+"-avg", *hist.SampleSum/n) + // TODO(obs-inf): add quantiles like for the hdrhistogram. + case prometheusMetricValuer: + // TODO we should be able to handle all non-histogram branches using this, i.e. + // can delete the float, int, etc, cases above. + _ = mtr.ToPrometheusMetric() + default: return errors.Errorf("cannot extract value for type %T", mtr) } diff --git a/pkg/util/metric/BUILD.bazel b/pkg/util/metric/BUILD.bazel index cf5b88fac4c5..5db5d0bfe2dc 100644 --- a/pkg/util/metric/BUILD.bazel +++ b/pkg/util/metric/BUILD.bazel @@ -14,8 +14,8 @@ go_library( "registry.go", "rule.go", "rule_registry.go", - "sliding_histogram.go", "test_helpers.go", + "tick_helper.go", ], embed = [":metric_go_proto"], importpath = "github.com/cockroachdb/cockroach/pkg/util/metric", diff --git a/pkg/util/metric/metric.go b/pkg/util/metric/metric.go index 2ce62329a5d3..f7d1c833b67e 100644 --- a/pkg/util/metric/metric.go +++ b/pkg/util/metric/metric.go @@ -20,6 +20,7 @@ import ( "github.com/cockroachdb/cockroach/pkg/util/timeutil" "github.com/codahale/hdrhistogram" "github.com/gogo/protobuf/proto" + "github.com/prometheus/client_golang/prometheus" prometheusgo "github.com/prometheus/client_model/go" metrics "github.com/rcrowley/go-metrics" ) @@ -185,7 +186,8 @@ type Histogram struct { mu struct { syncutil.Mutex cumulative *hdrhistogram.Histogram - sliding *slidingHistogram + *tickHelper + sliding *hdrhistogram.WindowedHistogram } } @@ -194,13 +196,20 @@ type Histogram struct { // track nonnegative values up to 'maxVal' with 'sigFigs' decimal points of // precision. func NewHistogram(metadata Metadata, duration time.Duration, maxVal int64, sigFigs int) *Histogram { - dHist := newSlidingHistogram(duration, maxVal, sigFigs) h := &Histogram{ Metadata: metadata, maxVal: maxVal, } + wHist := hdrhistogram.NewWindowed(histWrapNum, 0, maxVal, sigFigs) h.mu.cumulative = hdrhistogram.New(0, maxVal, sigFigs) - h.mu.sliding = dHist + h.mu.sliding = wHist + h.mu.tickHelper = &tickHelper{ + nextT: now(), + tickInterval: duration / histWrapNum, + onTick: func() { + wHist.Rotate() + }, + } return h } @@ -222,7 +231,9 @@ func NewLatency(metadata Metadata, histogramWindow time.Duration) *Histogram { func (h *Histogram) Windowed() (*hdrhistogram.Histogram, time.Duration) { h.mu.Lock() defer h.mu.Unlock() - return cloneHistogram(h.mu.sliding.Current()), h.mu.sliding.duration + // TODO(obs-inf): not sure we should multiply by histWrapNum here, but it + // has been the behavior for a long time. + return cloneHistogram(h.mu.sliding.Merge()), histWrapNum * h.mu.tickInterval } // Snapshot returns a copy of the cumulative (i.e. all-time samples) histogram @@ -240,8 +251,8 @@ func (h *Histogram) RecordValue(v int64) { h.mu.Lock() defer h.mu.Unlock() - if h.mu.sliding.RecordValue(v) != nil { - _ = h.mu.sliding.RecordValue(h.maxVal) + if h.mu.sliding.Current.RecordValue(v) != nil { + _ = h.mu.sliding.Current.RecordValue(h.maxVal) } if h.mu.cumulative.RecordValue(v) != nil { _ = h.mu.cumulative.RecordValue(h.maxVal) @@ -265,7 +276,7 @@ func (h *Histogram) Min() int64 { // Inspect calls the closure with the empty string and the receiver. func (h *Histogram) Inspect(f func(interface{})) { h.mu.Lock() - maybeTick(h.mu.sliding) + maybeTick(h.mu.tickHelper) h.mu.Unlock() f(h) } @@ -280,7 +291,7 @@ func (h *Histogram) ToPrometheusMetric() *prometheusgo.Metric { hist := &prometheusgo.Histogram{} h.mu.Lock() - maybeTick(h.mu.sliding) + maybeTick(h.mu.tickHelper) bars := h.mu.cumulative.Distribution() hist.Bucket = make([]*prometheusgo.Bucket, 0, len(bars)) @@ -319,6 +330,155 @@ func (h *Histogram) GetMetadata() Metadata { return baseMetadata } +// IOLatencyBuckets are prometheus histogram buckets suitable for a histogram +// that records a quantity (nanosecond-denominated) in which most measurements +// resemble those of typical disk latencies, i.e. which are in the micro- and +// millisecond range during normal operation. +var IOLatencyBuckets = []float64{ + // Generated via TestHistogramBuckets/IOLatencyBuckets. + 10000.000000, // 10µs + 26826.957953, // 26.826µs + 71968.567300, // 71.968µs + 193069.772888, // 193.069µs + 517947.467923, // 517.947µs + 1389495.494373, // 1.389495ms + 3727593.720315, // 3.727593ms + 10000000.000000, // 9.999999ms + 26826957.952797, // 26.826957ms + 71968567.300115, // 71.968567ms + 193069772.888325, // 193.069772ms + 517947467.923120, // 517.947467ms + 1389495494.373135, // 1.389495494s + 3727593720.314933, // 3.72759372s + 9999999999.999981, // 9.999999999s +} + +// NetworkLatencyBuckets are prometheus histogram buckets suitable for a histogram +// that records a quantity (nanosecond-denominated) in which most measurements +// behave like network latencies, i.e. most measurements are in the ms to sub-second +// range during normal operation. +var NetworkLatencyBuckets = []float64{ + // Generated via TestHistogramBuckets/NetworkLatencyBuckets. + 500000.000000, // 500µs + 860513.842995, // 860.513µs + 1480968.147973, // 1.480968ms + 2548787.184731, // 2.548787ms + 4386533.310619, // 4.386533ms + 7549345.273094, // 7.549345ms + 12992632.226094, // 12.992632ms + 22360679.774998, // 22.360679ms + 38483348.970335, // 38.483348ms + 66230909.027573, // 66.230909ms + 113985228.104760, // 113.985228ms + 196171733.362212, // 196.171733ms + 337616984.325077, // 337.616984ms + 581048177.284016, // 581.048177ms + 999999999.999999, // 999.999999ms, +} + +// NewHistogramV2 is a prometheus-backed histogram. Depending on the value of +// opts.Buckets, this is suitable for recording any kind of quantity. Common +// sensible choices are {IO,Network}LatencyBuckets. +func NewHistogramV2( + meta Metadata, windowDuration time.Duration, opts prometheus.HistogramOpts, +) *HistogramV2 { + // TODO(obs-inf): prometheus supports labeled histograms but they require more + // plumbing and don't fit into the PrometheusObservable interface any more. + cum := prometheus.NewHistogram(opts) + h := &HistogramV2{ + Metadata: meta, + cum: cum, + } + h.windowed.tickHelper = &tickHelper{ + nextT: now(), + tickInterval: windowDuration, + onTick: func() { + h.windowed.prev = h.windowed.cur + h.windowed.cur = prometheus.NewHistogram(opts) + }, + } + h.windowed.tickHelper.onTick() + return h +} + +var _ periodic = (*HistogramV2)(nil) +var _ PrometheusExportable = (*HistogramV2)(nil) + +type HistogramV2 struct { + Metadata + cum prometheus.Histogram + + // TODO(obs-inf): the way we implement windowed histograms is not great. If + // the windowed histogram is pulled right after a tick, it will be mostly + // empty. We could add a third bucket and represent the merged view of the two + // most recent buckets to avoid that. Or we could "just" double the rotation + // interval (so that the histogram really collects for 20s when we expect to + // persist the contents every 10s). Really it would make more sense to + // explicitly rotate the histogram atomically with collecting its contents, + // but that is now how we have set it up right now. It should be doable + // though, since there is only one consumer of windowed histograms - our + // internal timeseries system. + windowed struct { + // prometheus.Histogram is thread safe, so we only + // need an RLock to record into it. But write lock + // is held while rotating. + syncutil.RWMutex + *tickHelper + prev, cur prometheus.Histogram + } +} + +func (h *HistogramV2) nextTick() time.Time { + h.windowed.RLock() + defer h.windowed.RUnlock() + return h.windowed.nextTick() +} + +func (h *HistogramV2) tick() { + h.windowed.Lock() + defer h.windowed.Unlock() + h.windowed.tick() +} + +func (h *HistogramV2) Windowed() prometheus.Histogram { + h.windowed.RLock() + defer h.windowed.RUnlock() + return h.windowed.cur +} + +func (h *HistogramV2) RecordValue(n int64) { + v := float64(n) + h.cum.Observe(v) + + h.windowed.RLock() + defer h.windowed.RUnlock() + h.windowed.cur.Observe(v) + +} + +func (h *HistogramV2) GetType() *prometheusgo.MetricType { + return prometheusgo.MetricType_HISTOGRAM.Enum() +} + +func (h *HistogramV2) ToPrometheusMetric() *prometheusgo.Metric { + m := &prometheusgo.Metric{} + if err := h.cum.Write(m); err != nil { + panic(err) // TODD + } + return m +} + +func (h *HistogramV2) GetMetadata() Metadata { + return h.Metadata +} + +func (h *HistogramV2) Inspect(f func(interface{})) { + h.windowed.Lock() + maybeTick(&h.windowed) + h.windowed.Unlock() + f(h) +} + // A Counter holds a single mutable atomic value. type Counter struct { Metadata diff --git a/pkg/util/metric/metric_test.go b/pkg/util/metric/metric_test.go index 78f4aa040dcc..619886306d8e 100644 --- a/pkg/util/metric/metric_test.go +++ b/pkg/util/metric/metric_test.go @@ -13,15 +13,19 @@ package metric import ( "bytes" "encoding/json" + "fmt" "math" "reflect" + "strings" "sync" "testing" "time" _ "github.com/cockroachdb/cockroach/pkg/util/log" // for flags "github.com/kr/pretty" + "github.com/prometheus/client_golang/prometheus" prometheusgo "github.com/prometheus/client_model/go" + "github.com/stretchr/testify/require" ) func testMarshal(t *testing.T, m json.Marshaler, exp string) { @@ -135,6 +139,58 @@ func TestHistogramPrometheus(t *testing.T) { } } +func TestHistogramBuckets(t *testing.T) { + verifyAndPrint := func(t *testing.T, exp, act []float64) { + t.Helper() + var buf strings.Builder + for idx, f := range exp { + if idx == 0 { + fmt.Fprintf(&buf, "// Generated via %s.", t.Name()) + } + fmt.Fprintf(&buf, "\n%f, // %s", f, time.Duration(f)) + } + t.Logf("%s", &buf) + require.InDeltaSlice(t, exp, act, 1 /* delta */, "Please update the bucket boundaries for %s", t.Name()) + } + t.Run("IOLatencyBuckets", func(t *testing.T) { + exp := prometheus.ExponentialBucketsRange(10e3, 10e9, 15) + verifyAndPrint(t, exp, IOLatencyBuckets) + }) + + t.Run("NetworkLatencyBuckets", func(t *testing.T) { + exp := prometheus.ExponentialBucketsRange(500e3, 1e9, 15) + verifyAndPrint(t, exp, NetworkLatencyBuckets) + }) +} + +func TestNewHistogramV2Rotate(t *testing.T) { + defer TestingSetNow(nil)() + setNow(0) + + h := NewHistogramV2(emptyMetadata, 10*time.Second, prometheus.HistogramOpts{Buckets: nil}) + for i := 0; i < 4; i++ { + // Windowed histogram is initially empty. + h.Inspect(func(interface{}) {}) // triggers ticking + var m prometheusgo.Metric + require.NoError(t, h.Windowed().Write(&m)) + require.Zero(t, *m.Histogram.SampleSum) + // But cumulative histogram has history (if i > 0). + require.EqualValues(t, i, *h.ToPrometheusMetric().Histogram.SampleCount) + + // Add a measurement and verify it's there. + { + h.RecordValue(12345) + f := float64(12345) + var m prometheusgo.Metric + require.NoError(t, h.Windowed().Write(&m)) + require.Equal(t, *m.Histogram.SampleSum, f) + } + // Tick. This rotates the histogram. + setNow(time.Duration(i+1) * 10 * time.Second) + // Go to beginning. + } +} + func TestHistogramRotate(t *testing.T) { defer TestingSetNow(nil)() setNow(0) diff --git a/pkg/util/metric/sliding_histogram.go b/pkg/util/metric/sliding_histogram.go deleted file mode 100644 index 20262befc1ef..000000000000 --- a/pkg/util/metric/sliding_histogram.go +++ /dev/null @@ -1,61 +0,0 @@ -// Copyright 2015 The Cockroach Authors. -// -// Use of this software is governed by the Business Source License -// included in the file licenses/BSL.txt. -// -// As of the Change Date specified in that file, in accordance with -// the Business Source License, use of this software will be governed -// by the Apache License, Version 2.0, included in the file -// licenses/APL.txt. - -package metric - -import ( - "time" - - "github.com/codahale/hdrhistogram" -) - -var _ periodic = &slidingHistogram{} - -// A deprecatedWindowedHistogram is a wrapper around an -// hdrhistogram.WindowedHistogram. The caller must enforce proper -// synchronization. -type slidingHistogram struct { - windowed *hdrhistogram.WindowedHistogram - nextT time.Time - duration time.Duration -} - -// newSlidingHistogram creates a new windowed HDRHistogram with the given -// parameters. Data is kept in the active window for approximately the given -// duration. See the documentation for hdrhistogram.WindowedHistogram for -// details. -func newSlidingHistogram(duration time.Duration, maxVal int64, sigFigs int) *slidingHistogram { - if duration <= 0 { - panic("cannot create a sliding histogram with nonpositive duration") - } - return &slidingHistogram{ - nextT: now(), - duration: duration, - windowed: hdrhistogram.NewWindowed(histWrapNum, 0, maxVal, sigFigs), - } -} - -func (h *slidingHistogram) tick() { - h.nextT = h.nextT.Add(h.duration / histWrapNum) - h.windowed.Rotate() -} - -func (h *slidingHistogram) nextTick() time.Time { - return h.nextT -} - -func (h *slidingHistogram) Current() *hdrhistogram.Histogram { - maybeTick(h) - return h.windowed.Merge() -} - -func (h *slidingHistogram) RecordValue(v int64) error { - return h.windowed.Current.RecordValue(v) -} diff --git a/pkg/util/metric/tick_helper.go b/pkg/util/metric/tick_helper.go new file mode 100644 index 000000000000..fbc6ab19e96a --- /dev/null +++ b/pkg/util/metric/tick_helper.go @@ -0,0 +1,34 @@ +// Copyright 2015 The Cockroach Authors. +// +// Use of this software is governed by the Business Source License +// included in the file licenses/BSL.txt. +// +// As of the Change Date specified in that file, in accordance with +// the Business Source License, use of this software will be governed +// by the Apache License, Version 2.0, included in the file +// licenses/APL.txt. + +package metric + +import "time" + +var _ periodic = &tickHelper{} + +// tickHelper is used by metrics that are at heart cumulative, but wish to also +// maintain a windowed version to work around limitations of our internal +// timeseries database. +type tickHelper struct { + nextT time.Time + tickInterval time.Duration + + onTick func() +} + +func (s *tickHelper) nextTick() time.Time { + return s.nextT +} + +func (s *tickHelper) tick() { + s.nextT = s.nextT.Add(s.tickInterval) + s.onTick() +}