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chunk.go
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chunk.go
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// Copyright 2017 The Prometheus 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 chunkenc
import (
"math"
"sync"
"github.com/pkg/errors"
)
// Encoding is the identifier for a chunk encoding.
type Encoding uint8
func (e Encoding) String() string {
switch e {
case EncNone:
return "none"
case EncXOR:
return "XOR"
}
return "<unknown>"
}
// The different available chunk encodings.
const (
EncNone Encoding = iota
EncXOR
)
// Chunk holds a sequence of sample pairs that can be iterated over and appended to.
type Chunk interface {
// Bytes returns the underlying byte slice of the chunk.
Bytes() []byte
// Encoding returns the encoding type of the chunk.
Encoding() Encoding
// Appender returns an appender to append samples to the chunk.
Appender() (Appender, error)
// The iterator passed as argument is for re-use.
// Depending on implementation, the iterator can
// be re-used or a new iterator can be allocated.
Iterator(Iterator) Iterator
// NumSamples returns the number of samples in the chunk.
NumSamples() int
// Compact is called whenever a chunk is expected to be complete (no more
// samples appended) and the underlying implementation can eventually
// optimize the chunk.
// There's no strong guarantee that no samples will be appended once
// Compact() is called. Implementing this function is optional.
Compact()
}
// Appender adds sample pairs to a chunk.
type Appender interface {
Append(int64, float64)
}
// Iterator is a simple iterator that can only get the next value.
// Iterator iterates over the samples of a time series, in timestamp-increasing order.
type Iterator interface {
// Next advances the iterator by one.
Next() bool
// Seek advances the iterator forward to the first sample with the timestamp equal or greater than t.
// If current sample found by previous `Next` or `Seek` operation already has this property, Seek has no effect.
// Seek returns true, if such sample exists, false otherwise.
// Iterator is exhausted when the Seek returns false.
Seek(t int64) bool
// At returns the current timestamp/value pair.
// Before the iterator has advanced At behaviour is unspecified.
At() (int64, float64)
// Err returns the current error. It should be used only after iterator is
// exhausted, that is `Next` or `Seek` returns false.
Err() error
}
// NewNopIterator returns a new chunk iterator that does not hold any data.
func NewNopIterator() Iterator {
return nopIterator{}
}
type nopIterator struct{}
func (nopIterator) Seek(int64) bool { return false }
func (nopIterator) At() (int64, float64) { return math.MinInt64, 0 }
func (nopIterator) Next() bool { return false }
func (nopIterator) Err() error { return nil }
// Pool is used to create and reuse chunk references to avoid allocations.
type Pool interface {
Put(Chunk) error
Get(e Encoding, b []byte) (Chunk, error)
}
// pool is a memory pool of chunk objects.
type pool struct {
xor sync.Pool
}
// NewPool returns a new pool.
func NewPool() Pool {
return &pool{
xor: sync.Pool{
New: func() interface{} {
return &XORChunk{b: bstream{}}
},
},
}
}
func (p *pool) Get(e Encoding, b []byte) (Chunk, error) {
switch e {
case EncXOR:
c := p.xor.Get().(*XORChunk)
c.b.stream = b
c.b.count = 0
return c, nil
}
return nil, errors.Errorf("invalid chunk encoding %q", e)
}
func (p *pool) Put(c Chunk) error {
switch c.Encoding() {
case EncXOR:
xc, ok := c.(*XORChunk)
// This may happen often with wrapped chunks. Nothing we can really do about
// it but returning an error would cause a lot of allocations again. Thus,
// we just skip it.
if !ok {
return nil
}
xc.b.stream = nil
xc.b.count = 0
p.xor.Put(c)
default:
return errors.Errorf("invalid chunk encoding %q", c.Encoding())
}
return nil
}
// FromData returns a chunk from a byte slice of chunk data.
// This is there so that users of the library can easily create chunks from
// bytes.
func FromData(e Encoding, d []byte) (Chunk, error) {
switch e {
case EncXOR:
return &XORChunk{b: bstream{count: 0, stream: d}}, nil
}
return nil, errors.Errorf("invalid chunk encoding %q", e)
}