prometheus/promql/analyzer.go

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// Copyright 2013 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 promql
import (
"errors"
"time"
"golang.org/x/net/context"
clientmodel "github.com/prometheus/client_golang/model"
"github.com/prometheus/prometheus/storage/local"
)
// An Analyzer traverses an expression and determines which data has to be requested
// from the storage. It is bound to a context that allows cancellation and timing out.
type Analyzer struct {
// The storage from which to query data.
Storage local.Storage
// The expression being analyzed.
Expr Expr
// The time range for evaluation of Expr.
Start, End clientmodel.Timestamp
// The preload times for different query time offsets.
offsetPreloadTimes map[time.Duration]preloadTimes
}
// preloadTimes tracks which instants or ranges to preload for a set of
// fingerprints. One of these structs is collected for each offset by the query
// analyzer.
type preloadTimes struct {
// Instants require single samples to be loaded along the entire query
// range, with intervals between the samples corresponding to the query
// resolution.
instants map[clientmodel.Fingerprint]struct{}
// Ranges require loading a range of samples at each resolution step,
// stretching backwards from the current evaluation timestamp. The length of
// the range into the past is given by the duration, as in "foo[5m]".
ranges map[clientmodel.Fingerprint]time.Duration
}
// Analyze the provided expression and attach metrics and fingerprints to data-selecting
// AST nodes that are later used to preload the data from the storage.
func (a *Analyzer) Analyze(ctx context.Context) error {
a.offsetPreloadTimes = map[time.Duration]preloadTimes{}
getPreloadTimes := func(offset time.Duration) preloadTimes {
if _, ok := a.offsetPreloadTimes[offset]; !ok {
a.offsetPreloadTimes[offset] = preloadTimes{
instants: map[clientmodel.Fingerprint]struct{}{},
ranges: map[clientmodel.Fingerprint]time.Duration{},
}
}
return a.offsetPreloadTimes[offset]
}
// Retrieve fingerprints and metrics for the required time range for
// each metric or matrix selector node.
Inspect(a.Expr, func(node Node) bool {
switch n := node.(type) {
case *VectorSelector:
pt := getPreloadTimes(n.Offset)
fpts := a.Storage.FingerprintsForLabelMatchers(n.LabelMatchers)
n.fingerprints = fpts
n.metrics = map[clientmodel.Fingerprint]clientmodel.COWMetric{}
n.iterators = map[clientmodel.Fingerprint]local.SeriesIterator{}
for _, fp := range fpts {
// Only add the fingerprint to the instants if not yet present in the
// ranges. Ranges always contain more points and span more time than
// instants for the same offset.
if _, alreadyInRanges := pt.ranges[fp]; !alreadyInRanges {
pt.instants[fp] = struct{}{}
}
n.metrics[fp] = a.Storage.MetricForFingerprint(fp)
}
case *MatrixSelector:
pt := getPreloadTimes(n.Offset)
fpts := a.Storage.FingerprintsForLabelMatchers(n.LabelMatchers)
n.fingerprints = fpts
n.metrics = map[clientmodel.Fingerprint]clientmodel.COWMetric{}
n.iterators = map[clientmodel.Fingerprint]local.SeriesIterator{}
for _, fp := range fpts {
if pt.ranges[fp] < n.Range {
pt.ranges[fp] = n.Range
// Delete the fingerprint from the instants. Ranges always contain more
// points and span more time than instants, so we don't need to track
// an instant for the same fingerprint, should we have one.
delete(pt.instants, fp)
}
n.metrics[fp] = a.Storage.MetricForFingerprint(fp)
}
}
return true
})
// Currently we do not return an error but we might place a context check in here
// or extend the stage in some other way.
return nil
}
// Prepare the expression evaluation by preloading all required chunks from the storage
// and setting the respective storage iterators in the AST nodes.
func (a *Analyzer) Prepare(ctx context.Context) (local.Preloader, error) {
const env = "query preparation"
if a.offsetPreloadTimes == nil {
return nil, errors.New("analysis must be performed before preparing query")
}
var err error
// The preloader must not be closed unless an error ocurred as closing
// unpins the preloaded chunks.
p := a.Storage.NewPreloader()
defer func() {
if err != nil {
p.Close()
}
}()
// Preload all analyzed ranges.
for offset, pt := range a.offsetPreloadTimes {
start := a.Start.Add(-offset)
end := a.End.Add(-offset)
for fp, rangeDuration := range pt.ranges {
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if err = contextDone(ctx, env); err != nil {
return nil, err
}
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err = p.PreloadRange(fp, start.Add(-rangeDuration), end, StalenessDelta)
if err != nil {
return nil, err
}
}
for fp := range pt.instants {
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if err = contextDone(ctx, env); err != nil {
return nil, err
}
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err = p.PreloadRange(fp, start, end, StalenessDelta)
if err != nil {
return nil, err
}
}
}
// Attach storage iterators to AST nodes.
Inspect(a.Expr, func(node Node) bool {
switch n := node.(type) {
case *VectorSelector:
for _, fp := range n.fingerprints {
n.iterators[fp] = a.Storage.NewIterator(fp)
}
case *MatrixSelector:
for _, fp := range n.fingerprints {
n.iterators[fp] = a.Storage.NewIterator(fp)
}
}
return true
})
return p, nil
}