prometheus/storage/memoized_iterator.go

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// Copyright 2021 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 storage
import (
"math"
"github.com/prometheus/prometheus/tsdb/chunkenc"
)
// MemoizedSeriesIterator wraps an iterator with a buffer to look back the previous element.
type MemoizedSeriesIterator struct {
it chunkenc.Iterator
delta int64
lastTime int64
ok bool
// Keep track of the previously returned value.
prevTime int64
prevValue float64
}
// NewMemoizedEmptyIterator is like NewMemoizedIterator but it's initialised with an empty iterator.
func NewMemoizedEmptyIterator(delta int64) *MemoizedSeriesIterator {
return NewMemoizedIterator(chunkenc.NewNopIterator(), delta)
}
// NewMemoizedIterator returns a new iterator that buffers the values within the
// time range of the current element and the duration of delta before.
func NewMemoizedIterator(it chunkenc.Iterator, delta int64) *MemoizedSeriesIterator {
bit := &MemoizedSeriesIterator{
delta: delta,
prevTime: math.MinInt64,
}
bit.Reset(it)
return bit
}
// Reset the internal state to reuse the wrapper with the provided iterator.
func (b *MemoizedSeriesIterator) Reset(it chunkenc.Iterator) {
b.it = it
b.lastTime = math.MinInt64
b.ok = true
b.prevTime = math.MinInt64
it.Next()
}
// PeekPrev returns the previous element of the iterator. If there is none buffered,
// ok is false.
func (b *MemoizedSeriesIterator) PeekPrev() (t int64, v float64, ok bool) {
if b.prevTime == math.MinInt64 {
return 0, 0, false
}
return b.prevTime, b.prevValue, true
}
// Seek advances the iterator to the element at time t or greater.
func (b *MemoizedSeriesIterator) Seek(t int64) bool {
t0 := t - b.delta
if t0 > b.lastTime {
// Reset the previously stored element because the seek advanced
// more than the delta.
b.prevTime = math.MinInt64
b.ok = b.it.Seek(t0)
if !b.ok {
return false
}
b.lastTime, _ = b.it.At()
}
if b.lastTime >= t {
return true
}
for b.Next() {
if b.lastTime >= t {
return true
}
}
return false
}
// Next advances the iterator to the next element.
func (b *MemoizedSeriesIterator) Next() bool {
if !b.ok {
return false
}
// Keep track of the previous element.
b.prevTime, b.prevValue = b.it.At()
b.ok = b.it.Next()
if b.ok {
b.lastTime, _ = b.it.At()
}
return b.ok
}
// Values returns the current element of the iterator.
func (b *MemoizedSeriesIterator) Values() (int64, float64) {
return b.it.At()
}
// Err returns the last encountered error.
func (b *MemoizedSeriesIterator) Err() error {
return b.it.Err()
}