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Add a Downsampling writer that drop a percentage of spans (#1353)
* adding a wrapping writer that automatic drop spans before writing with predefined config Signed-off-by: Jude Wang <judew@uber.com> * updating comment Signed-off-by: Jude Wang <judew@uber.com> * hash traceID for downsampling and code refactoring Signed-off-by: Jude Wang <judew@uber.com> * adding DownSamplingOptions Signed-off-by: Jude Wang <judew@uber.com> * address yuri's comments Signed-off-by: Jude Wang <judew@uber.com> * committing benchmark file & adding metrics Signed-off-by: Jude Wang <judew@uber.com> * address comment from Won Signed-off-by: Jude Wang <judew@uber.com> * get rid of defer; benchmark sync.Pool for byte array; make sure 100% code coverage Signed-off-by: Jude Wang <judew@uber.com> * making sure sync.Pool benchmark with 0 allocations Signed-off-by: Jude Wang <judew@uber.com> * refactor to read ratio and hashsalt from CLI Signed-off-by: Jude Wang <judew@uber.com> * address yuri comments Signed-off-by: Jude Wang <judew@uber.com> * refinement Signed-off-by: Jude Wang <judew@uber.com> * fix merge conflict Signed-off-by: Jude Wang <judew@uber.com> * copy hashSalt slice inside bytePool initialization Signed-off-by: Jude Wang <judew@uber.com> * further comments from yuri Signed-off-by: Jude Wang <judew@uber.com> * omit error check for MarshalTo Signed-off-by: Jude Wang <judew@uber.com> * update naming and some logic Signed-off-by: Jude Wang <judew@uber.com> * remove pointer Signed-off-by: Jude Wang <judew@uber.com> * updating tests Signed-off-by: Jude Wang <judew@uber.com> * adding default salt Signed-off-by: Jude Wang <judew@uber.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,119 @@ | ||
| // Copyright (c) 2019 The Jaeger 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 spanstore | ||
|
|
||
| import ( | ||
| "hash" | ||
| "hash/fnv" | ||
| "math" | ||
| "sync" | ||
|
|
||
| "github.com/uber/jaeger-lib/metrics" | ||
|
|
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| "github.com/jaegertracing/jaeger/model" | ||
| ) | ||
|
|
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| const defaultHashSalt = "downsampling-default-salt" | ||
|
|
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| var ( | ||
| traceIDByteSize = (&model.TraceID{}).Size() | ||
| ) | ||
|
|
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| // hasher includes data we want to put in sync.Pool. | ||
| type hasher struct { | ||
| hash hash.Hash64 | ||
| buffer []byte | ||
| } | ||
|
|
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| // downsamplingWriterMetrics keeping track of total number of dropped spans and accepted spans. | ||
| type downsamplingWriterMetrics struct { | ||
| SpansDropped metrics.Counter `metric:"spans_dropped"` | ||
| SpansAccepted metrics.Counter `metric:"spans_accepted"` | ||
| } | ||
|
|
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| // DownsamplingWriter is a span Writer that drops spans with a predefined downsamplingRatio. | ||
| type DownsamplingWriter struct { | ||
| spanWriter Writer | ||
| threshold uint64 | ||
| lengthOfSalt int | ||
| hasherPool *sync.Pool | ||
| metrics downsamplingWriterMetrics | ||
| } | ||
|
|
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| // DownsamplingOptions contains the options for constructing a DownsamplingWriter. | ||
| type DownsamplingOptions struct { | ||
| Ratio float64 | ||
| HashSalt string | ||
| MetricsFactory metrics.Factory | ||
| } | ||
|
|
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| // NewDownsamplingWriter creates a DownsamplingWriter. | ||
| func NewDownsamplingWriter(spanWriter Writer, downsamplingOptions DownsamplingOptions) *DownsamplingWriter { | ||
| threshold := uint64(downsamplingOptions.Ratio * float64(math.MaxUint64)) | ||
| writeMetrics := &downsamplingWriterMetrics{} | ||
| metrics.Init(writeMetrics, downsamplingOptions.MetricsFactory, nil) | ||
| salt := downsamplingOptions.HashSalt | ||
| if salt == "" { | ||
| salt = defaultHashSalt | ||
| } | ||
| hashSaltBytes := []byte(salt) | ||
| pool := &sync.Pool{ | ||
| New: func() interface{} { | ||
| buffer := make([]byte, len(hashSaltBytes)+traceIDByteSize) | ||
| copy(buffer, hashSaltBytes) | ||
| return &hasher{ | ||
| hash: fnv.New64a(), | ||
| buffer: buffer, | ||
| } | ||
| }, | ||
| } | ||
|
|
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| return &DownsamplingWriter{ | ||
| spanWriter: spanWriter, | ||
| threshold: threshold, | ||
| hasherPool: pool, | ||
| metrics: *writeMetrics, | ||
| lengthOfSalt: len(hashSaltBytes), | ||
| } | ||
| } | ||
|
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| // WriteSpan calls WriteSpan on wrapped span writer. | ||
| func (ds *DownsamplingWriter) WriteSpan(span *model.Span) error { | ||
| if !ds.shouldDownsample(span) { | ||
| // Drops spans when hashVal falls beyond computed threshold. | ||
| ds.metrics.SpansDropped.Inc(1) | ||
| return nil | ||
| } | ||
| ds.metrics.SpansAccepted.Inc(1) | ||
| return ds.spanWriter.WriteSpan(span) | ||
| } | ||
|
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| func (ds *DownsamplingWriter) shouldDownsample(span *model.Span) bool { | ||
| hasherInstance := ds.hasherPool.Get().(*hasher) | ||
| // Currently MarshalTo will only return err if size of traceIDBytes is smaller than 16 | ||
| // Since we force traceIDBytes to be size of 16 metrics is not necessary here. | ||
| _, _ = span.TraceID.MarshalTo(hasherInstance.buffer[ds.lengthOfSalt:]) | ||
| hashVal := hasherInstance.hashBytes() | ||
| ds.hasherPool.Put(hasherInstance) | ||
| return hashVal <= ds.threshold | ||
| } | ||
|
|
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| // hashBytes returns the uint64 hash value of byte slice. | ||
| func (h *hasher) hashBytes() uint64 { | ||
| h.hash.Reset() | ||
| // Currently fnv.Write() implementation doesn't throw any error so metric is not necessary here. | ||
| _, _ = h.hash.Write(h.buffer) | ||
| return h.hash.Sum64() | ||
| } |
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