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memstore.go
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memstore.go
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package main
import (
"errors"
"sync"
"unsafe"
)
// Default buffer capacity.
// `buffer.data` will only ever grow up to it's capacity and a new link
// in the buffer chain will be created if needed so that no copying
// of data or reallocation needs to happen on writes.
const (
BUFFER_CAP int = 512
)
// So that we can reuse allocations
var bufferPool sync.Pool = sync.Pool{
New: func() interface{} {
return &buffer{
data: make([]Float, 0, BUFFER_CAP),
}
},
}
var (
ErrNoData error = errors.New("no data for this metric/level")
ErrDataDoesNotAlign error = errors.New("data from lower granularities does not align")
)
// Each metric on each level has it's own buffer.
// This is where the actual values go.
// If `cap(data)` is reached, a new buffer is created and
// becomes the new head of a buffer list.
type buffer struct {
frequency int64 // Time between two "slots"
start int64 // Timestamp of when `data[0]` was written.
data []Float // The slice should never reallocacte as `cap(data)` is respected.
prev, next *buffer // `prev` contains older data, `next` newer data.
archived bool // If true, this buffer is already archived
closed bool
/*
statisticts struct {
samples int
min Float
max Float
avg Float
}
*/
}
func newBuffer(ts, freq int64) *buffer {
b := bufferPool.Get().(*buffer)
b.frequency = freq
b.start = ts - (freq / 2)
b.prev = nil
b.next = nil
b.archived = false
b.closed = false
b.data = b.data[:0]
return b
}
// If a new buffer was created, the new head is returnd.
// Otherwise, the existing buffer is returnd.
// Normaly, only "newer" data should be written, but if the value would
// end up in the same buffer anyways it is allowed.
func (b *buffer) write(ts int64, value Float) (*buffer, error) {
if ts < b.start {
return nil, errors.New("cannot write value to buffer from past")
}
// idx := int((ts - b.start + (b.frequency / 3)) / b.frequency)
idx := int((ts - b.start) / b.frequency)
if idx >= cap(b.data) {
newbuf := newBuffer(ts, b.frequency)
newbuf.prev = b
b.next = newbuf
b.close()
b = newbuf
idx = 0
}
// Overwriting value or writing value from past
if idx < len(b.data) {
b.data[idx] = value
return b, nil
}
// Fill up unwritten slots with NaN
for i := len(b.data); i < idx; i++ {
b.data = append(b.data, NaN)
}
b.data = append(b.data, value)
return b, nil
}
func (b *buffer) end() int64 {
return b.firstWrite() + int64(len(b.data))*b.frequency
}
func (b *buffer) firstWrite() int64 {
return b.start + (b.frequency / 2)
}
func (b *buffer) close() {}
/*
func (b *buffer) close() {
if b.closed {
return
}
b.closed = true
n, sum, min, max := 0, 0., math.MaxFloat64, -math.MaxFloat64
for _, x := range b.data {
if x.IsNaN() {
continue
}
n += 1
f := float64(x)
sum += f
min = math.Min(min, f)
max = math.Max(max, f)
}
b.statisticts.samples = n
if n > 0 {
b.statisticts.avg = Float(sum / float64(n))
b.statisticts.min = Float(min)
b.statisticts.max = Float(max)
} else {
b.statisticts.avg = NaN
b.statisticts.min = NaN
b.statisticts.max = NaN
}
}
*/
// func interpolate(idx int, data []Float) Float {
// if idx == 0 || idx+1 == len(data) {
// return NaN
// }
// return (data[idx-1] + data[idx+1]) / 2.0
// }
// Return all known values from `from` to `to`. Gaps of information are represented as NaN.
// Simple linear interpolation is done between the two neighboring cells if possible.
// If values at the start or end are missing, instead of NaN values, the second and thrid
// return values contain the actual `from`/`to`.
// This function goes back the buffer chain if `from` is older than the currents buffer start.
// The loaded values are added to `data` and `data` is returned, possibly with a shorter length.
// If `data` is not long enough to hold all values, this function will panic!
func (b *buffer) read(from, to int64, data []Float) ([]Float, int64, int64, error) {
if from < b.firstWrite() {
if b.prev != nil {
return b.prev.read(from, to, data)
}
from = b.firstWrite()
}
var i int = 0
var t int64 = from
for ; t < to; t += b.frequency {
idx := int((t - b.start) / b.frequency)
if idx >= cap(b.data) {
if b.next == nil {
break
}
b = b.next
idx = 0
}
if idx >= len(b.data) {
if b.next == nil || to <= b.next.start {
break
}
data[i] += NaN
} else if t < b.start {
data[i] += NaN
// } else if b.data[idx].IsNaN() {
// data[i] += interpolate(idx, b.data)
} else {
data[i] += b.data[idx]
}
i++
}
return data[:i], from, t, nil
}
// Returns true if this buffer needs to be freed.
func (b *buffer) free(t int64) (delme bool, n int) {
if b.prev != nil {
delme, m := b.prev.free(t)
n += m
if delme {
b.prev.next = nil
if cap(b.prev.data) == BUFFER_CAP {
bufferPool.Put(b.prev)
}
b.prev = nil
}
}
end := b.end()
if end < t {
return true, n + 1
}
return false, n
}
// Call `callback` on every buffer that contains data in the range from `from` to `to`.
func (b *buffer) iterFromTo(from, to int64, callback func(b *buffer) error) error {
if b == nil {
return nil
}
if err := b.prev.iterFromTo(from, to, callback); err != nil {
return err
}
if from <= b.end() && b.start <= to {
return callback(b)
}
return nil
}
func (b *buffer) count() int64 {
res := int64(len(b.data))
if b.prev != nil {
res += b.prev.count()
}
return res
}
// Could also be called "node" as this forms a node in a tree structure.
// Called level because "node" might be confusing here.
// Can be both a leaf or a inner node. In this tree structue, inner nodes can
// also hold data (in `metrics`).
type level struct {
lock sync.RWMutex
metrics []*buffer // Every level can store metrics.
children map[string]*level // Lower levels.
}
// Find the correct level for the given selector, creating it if
// it does not exist. Example selector in the context of the
// ClusterCockpit could be: []string{ "emmy", "host123", "cpu0" }.
// This function would probably benefit a lot from `level.children` beeing a `sync.Map`?
func (l *level) findLevelOrCreate(selector []string, nMetrics int) *level {
if len(selector) == 0 {
return l
}
// Allow concurrent reads:
l.lock.RLock()
var child *level
var ok bool
if l.children == nil {
// Children map needs to be created...
l.lock.RUnlock()
} else {
child, ok := l.children[selector[0]]
l.lock.RUnlock()
if ok {
return child.findLevelOrCreate(selector[1:], nMetrics)
}
}
// The level does not exist, take write lock for unqiue access:
l.lock.Lock()
// While this thread waited for the write lock, another thread
// could have created the child node.
if l.children != nil {
child, ok = l.children[selector[0]]
if ok {
l.lock.Unlock()
return child.findLevelOrCreate(selector[1:], nMetrics)
}
}
child = &level{
metrics: make([]*buffer, nMetrics),
children: nil,
}
if l.children != nil {
l.children[selector[0]] = child
} else {
l.children = map[string]*level{selector[0]: child}
}
l.lock.Unlock()
return child.findLevelOrCreate(selector[1:], nMetrics)
}
func (l *level) free(t int64) (int, error) {
l.lock.Lock()
defer l.lock.Unlock()
n := 0
for i, b := range l.metrics {
if b != nil {
delme, m := b.free(t)
n += m
if delme {
if cap(b.data) == BUFFER_CAP {
bufferPool.Put(b)
}
l.metrics[i] = nil
}
}
}
for _, l := range l.children {
m, err := l.free(t)
n += m
if err != nil {
return n, err
}
}
return n, nil
}
func (l *level) sizeInBytes() int64 {
l.lock.RLock()
defer l.lock.RUnlock()
size := int64(0)
for _, b := range l.metrics {
if b != nil {
size += b.count() * int64(unsafe.Sizeof(Float(0)))
}
}
for _, child := range l.children {
size += child.sizeInBytes()
}
return size
}
type MemoryStore struct {
root level // root of the tree structure
metrics map[string]MetricConfig
}
// Return a new, initialized instance of a MemoryStore.
// Will panic if values in the metric configurations are invalid.
func NewMemoryStore(metrics map[string]MetricConfig) *MemoryStore {
offset := 0
for key, config := range metrics {
if config.Frequency == 0 {
panic("invalid frequency")
}
metrics[key] = MetricConfig{
Frequency: config.Frequency,
Aggregation: config.Aggregation,
offset: offset,
}
offset += 1
}
return &MemoryStore{
root: level{
metrics: make([]*buffer, len(metrics)),
children: make(map[string]*level),
},
metrics: metrics,
}
}
// Write all values in `metrics` to the level specified by `selector` for time `ts`.
// Look at `findLevelOrCreate` for how selectors work.
func (m *MemoryStore) Write(selector []string, ts int64, metrics []Metric) error {
var ok bool
for i, metric := range metrics {
if metric.mc.Frequency == 0 {
metric.mc, ok = m.metrics[metric.Name]
if !ok {
metric.mc.Frequency = 0
}
metrics[i] = metric
}
}
return m.WriteToLevel(&m.root, selector, ts, metrics)
}
func (m *MemoryStore) GetLevel(selector []string) *level {
return m.root.findLevelOrCreate(selector, len(m.metrics))
}
// Assumes that `minfo` in `metrics` is filled in!
func (m *MemoryStore) WriteToLevel(l *level, selector []string, ts int64, metrics []Metric) error {
l = l.findLevelOrCreate(selector, len(m.metrics))
l.lock.Lock()
defer l.lock.Unlock()
for _, metric := range metrics {
if metric.mc.Frequency == 0 {
continue
}
b := l.metrics[metric.mc.offset]
if b == nil {
// First write to this metric and level
b = newBuffer(ts, metric.mc.Frequency)
l.metrics[metric.mc.offset] = b
}
nb, err := b.write(ts, metric.Value)
if err != nil {
return err
}
// Last write created a new buffer...
if b != nb {
l.metrics[metric.mc.offset] = nb
}
}
return nil
}
// Returns all values for metric `metric` from `from` to `to` for the selected level(s).
// If the level does not hold the metric itself, the data will be aggregated recursively from the children.
// The second and third return value are the actual from/to for the data. Those can be different from
// the range asked for if no data was available.
func (m *MemoryStore) Read(selector Selector, metric string, from, to int64) ([]Float, int64, int64, error) {
if from > to {
return nil, 0, 0, errors.New("invalid time range")
}
minfo, ok := m.metrics[metric]
if !ok {
return nil, 0, 0, errors.New("unkown metric: " + metric)
}
n, data := 0, make([]Float, (to-from)/minfo.Frequency+1)
err := m.root.findBuffers(selector, minfo.offset, func(b *buffer) error {
cdata, cfrom, cto, err := b.read(from, to, data)
if err != nil {
return err
}
if n == 0 {
from, to = cfrom, cto
} else if from != cfrom || to != cto || len(data) != len(cdata) {
missingfront, missingback := int((from-cfrom)/minfo.Frequency), int((to-cto)/minfo.Frequency)
if missingfront != 0 {
return ErrDataDoesNotAlign
}
newlen := len(cdata) - missingback
if newlen < 1 {
return ErrDataDoesNotAlign
}
cdata = cdata[0:newlen]
if len(cdata) != len(data) {
return ErrDataDoesNotAlign
}
from, to = cfrom, cto
}
data = cdata
n += 1
return nil
})
if err != nil {
return nil, 0, 0, err
} else if n == 0 {
return nil, 0, 0, errors.New("metric or host not found")
} else if n > 1 {
if minfo.Aggregation == AvgAggregation {
normalize := 1. / Float(n)
for i := 0; i < len(data); i++ {
data[i] *= normalize
}
} else if minfo.Aggregation != SumAggregation {
return nil, 0, 0, errors.New("invalid aggregation")
}
}
return data, from, to, nil
}
// Release all buffers for the selected level and all its children that contain only
// values older than `t`.
func (m *MemoryStore) Free(selector []string, t int64) (int, error) {
return m.GetLevel(selector).free(t)
}
func (m *MemoryStore) FreeAll() error {
for k := range m.root.children {
delete(m.root.children, k)
}
return nil
}
func (m *MemoryStore) SizeInBytes() int64 {
return m.root.sizeInBytes()
}
// Given a selector, return a list of all children of the level selected.
func (m *MemoryStore) ListChildren(selector []string) []string {
lvl := &m.root
for lvl != nil && len(selector) != 0 {
lvl.lock.RLock()
next := lvl.children[selector[0]]
lvl.lock.RUnlock()
lvl = next
selector = selector[1:]
}
if lvl == nil {
return nil
}
lvl.lock.RLock()
defer lvl.lock.RUnlock()
children := make([]string, 0, len(lvl.children))
for child := range lvl.children {
children = append(children, child)
}
return children
}