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https://github.com/prometheus/prometheus.git
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03a2313f7a
* dont waste space on the chunkRefMap * add time factor * add comments * better readability * add instrumentation and more comments * formatting * uppercase comments * Address review feedback. Renamed "free" to "shrink" everywhere, updated comments and threshold to 1000. * double space Signed-off-by: Mauro Stettler <mauro.stettler@gmail.com> Co-authored-by: Peter Štibraný <pstibrany@gmail.com> Co-authored-by: Mauro Stettler <mauro.stettler@gmail.com>
244 lines
7 KiB
Go
244 lines
7 KiB
Go
// Copyright 2021 The Prometheus Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package chunks
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import (
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"errors"
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"sync"
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"time"
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"github.com/prometheus/client_golang/prometheus"
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"github.com/prometheus/prometheus/tsdb/chunkenc"
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)
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const (
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// Minimum recorded peak since since the last shrinking of chunkWriteQueue.chunkrefMap to shrink it again.
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chunkRefMapShrinkThreshold = 1000
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// Minimum interval between shrinking of chunkWriteQueue.chunkRefMap.
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chunkRefMapMinShrinkInterval = 10 * time.Minute
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)
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type chunkWriteJob struct {
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cutFile bool
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seriesRef HeadSeriesRef
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mint int64
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maxt int64
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chk chunkenc.Chunk
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ref ChunkDiskMapperRef
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callback func(error)
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}
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// chunkWriteQueue is a queue for writing chunks to disk in a non-blocking fashion.
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// Chunks that shall be written get added to the queue, which is consumed asynchronously.
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// Adding jobs to the queue is non-blocking as long as the queue isn't full.
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type chunkWriteQueue struct {
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jobs chan chunkWriteJob
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chunkRefMapMtx sync.RWMutex
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chunkRefMap map[ChunkDiskMapperRef]chunkenc.Chunk
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chunkRefMapPeakSize int // Largest size that chunkRefMap has grown to since the last time we shrank it.
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chunkRefMapLastShrink time.Time // When the chunkRefMap has been shrunk the last time.
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// isRunningMtx serves two purposes:
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// 1. It protects isRunning field.
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// 2. It serializes adding of jobs to the chunkRefMap in addJob() method. If jobs channel is full then addJob() will block
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// while holding this mutex, which guarantees that chunkRefMap won't ever grow beyond the queue size + 1.
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isRunningMtx sync.Mutex
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isRunning bool // Used to prevent that new jobs get added to the queue when the chan is already closed.
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workerWg sync.WaitGroup
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writeChunk writeChunkF
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// Keeping separate counters instead of only a single CounterVec to improve the performance of the critical
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// addJob() method which otherwise would need to perform a WithLabelValues call on the CounterVec.
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adds prometheus.Counter
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gets prometheus.Counter
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completed prometheus.Counter
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shrink prometheus.Counter
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}
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// writeChunkF is a function which writes chunks, it is dynamic to allow mocking in tests.
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type writeChunkF func(HeadSeriesRef, int64, int64, chunkenc.Chunk, ChunkDiskMapperRef, bool) error
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func newChunkWriteQueue(reg prometheus.Registerer, size int, writeChunk writeChunkF) *chunkWriteQueue {
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counters := prometheus.NewCounterVec(
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prometheus.CounterOpts{
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Name: "prometheus_tsdb_chunk_write_queue_operations_total",
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Help: "Number of operations on the chunk_write_queue.",
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},
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[]string{"operation"},
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)
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q := &chunkWriteQueue{
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jobs: make(chan chunkWriteJob, size),
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chunkRefMap: make(map[ChunkDiskMapperRef]chunkenc.Chunk),
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chunkRefMapLastShrink: time.Now(),
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writeChunk: writeChunk,
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adds: counters.WithLabelValues("add"),
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gets: counters.WithLabelValues("get"),
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completed: counters.WithLabelValues("complete"),
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shrink: counters.WithLabelValues("shrink"),
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}
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if reg != nil {
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reg.MustRegister(counters)
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}
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q.start()
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return q
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}
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func (c *chunkWriteQueue) start() {
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c.workerWg.Add(1)
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go func() {
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defer c.workerWg.Done()
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for job := range c.jobs {
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c.processJob(job)
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}
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}()
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c.isRunningMtx.Lock()
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c.isRunning = true
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c.isRunningMtx.Unlock()
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}
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func (c *chunkWriteQueue) processJob(job chunkWriteJob) {
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err := c.writeChunk(job.seriesRef, job.mint, job.maxt, job.chk, job.ref, job.cutFile)
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if job.callback != nil {
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job.callback(err)
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}
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c.chunkRefMapMtx.Lock()
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defer c.chunkRefMapMtx.Unlock()
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delete(c.chunkRefMap, job.ref)
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c.completed.Inc()
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c.shrinkChunkRefMap()
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}
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// shrinkChunkRefMap checks whether the conditions to shrink the chunkRefMap are met,
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// if so chunkRefMap is reinitialized. The chunkRefMapMtx must be held when calling this method.
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//
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// We do this because Go runtime doesn't release internal memory used by map after map has been emptied.
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// To achieve that we create new map instead and throw the old one away.
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func (c *chunkWriteQueue) shrinkChunkRefMap() {
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if len(c.chunkRefMap) > 0 {
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// Can't shrink it while there is data in it.
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return
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}
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if c.chunkRefMapPeakSize < chunkRefMapShrinkThreshold {
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// Not shrinking it because it has not grown to the minimum threshold yet.
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return
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}
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now := time.Now()
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if now.Sub(c.chunkRefMapLastShrink) < chunkRefMapMinShrinkInterval {
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// Not shrinking it because the minimum duration between shrink-events has not passed yet.
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return
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}
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// Re-initialize the chunk ref map to half of the peak size that it has grown to since the last re-init event.
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// We are trying to hit the sweet spot in the trade-off between initializing it to a very small size
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// potentially resulting in many allocations to re-grow it, and initializing it to a large size potentially
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// resulting in unused allocated memory.
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c.chunkRefMap = make(map[ChunkDiskMapperRef]chunkenc.Chunk, c.chunkRefMapPeakSize/2)
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c.chunkRefMapPeakSize = 0
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c.chunkRefMapLastShrink = now
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c.shrink.Inc()
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}
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func (c *chunkWriteQueue) addJob(job chunkWriteJob) (err error) {
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defer func() {
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if err == nil {
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c.adds.Inc()
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}
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}()
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c.isRunningMtx.Lock()
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defer c.isRunningMtx.Unlock()
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if !c.isRunning {
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return errors.New("queue is not running")
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}
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c.chunkRefMapMtx.Lock()
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c.chunkRefMap[job.ref] = job.chk
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// Keep track of the peak usage of c.chunkRefMap.
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if len(c.chunkRefMap) > c.chunkRefMapPeakSize {
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c.chunkRefMapPeakSize = len(c.chunkRefMap)
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}
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c.chunkRefMapMtx.Unlock()
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c.jobs <- job
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return nil
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}
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func (c *chunkWriteQueue) get(ref ChunkDiskMapperRef) chunkenc.Chunk {
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c.chunkRefMapMtx.RLock()
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defer c.chunkRefMapMtx.RUnlock()
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chk, ok := c.chunkRefMap[ref]
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if ok {
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c.gets.Inc()
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}
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return chk
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}
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func (c *chunkWriteQueue) stop() {
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c.isRunningMtx.Lock()
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defer c.isRunningMtx.Unlock()
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if !c.isRunning {
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return
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}
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c.isRunning = false
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close(c.jobs)
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c.workerWg.Wait()
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}
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func (c *chunkWriteQueue) queueIsEmpty() bool {
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return c.queueSize() == 0
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}
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func (c *chunkWriteQueue) queueIsFull() bool {
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// When the queue is full and blocked on the writer the chunkRefMap has one more job than the cap of the jobCh
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// because one job is currently being processed and blocked in the writer.
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return c.queueSize() == cap(c.jobs)+1
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}
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func (c *chunkWriteQueue) queueSize() int {
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c.chunkRefMapMtx.Lock()
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defer c.chunkRefMapMtx.Unlock()
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// Looking at chunkRefMap instead of jobCh because the job is popped from the chan before it has
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// been fully processed, it remains in the chunkRefMap until the processing is complete.
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return len(c.chunkRefMap)
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}
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