202 lines
6.1 KiB
Go
202 lines
6.1 KiB
Go
// Copyright 2014 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 metric
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import (
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"fmt"
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"regexp"
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"strings"
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"github.com/prometheus/common/model"
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)
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// MatchType is an enum for label matching types.
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type MatchType int
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// Possible MatchTypes.
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const (
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Equal MatchType = iota
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NotEqual
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RegexMatch
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RegexNoMatch
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)
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func (m MatchType) String() string {
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typeToStr := map[MatchType]string{
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Equal: "=",
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NotEqual: "!=",
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RegexMatch: "=~",
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RegexNoMatch: "!~",
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}
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if str, ok := typeToStr[m]; ok {
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return str
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}
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panic("unknown match type")
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}
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// LabelMatchers is a slice of LabelMatcher objects. By implementing the
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// sort.Interface, it is sortable by cardinality score, i.e. after sorting, the
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// LabelMatcher that is expected to yield the fewest matches is first in the
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// slice, and LabelMatchers that match the empty string are last.
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type LabelMatchers []*LabelMatcher
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func (lms LabelMatchers) Len() int { return len(lms) }
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func (lms LabelMatchers) Swap(i, j int) { lms[i], lms[j] = lms[j], lms[i] }
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func (lms LabelMatchers) Less(i, j int) bool { return lms[i].score < lms[j].score }
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// LabelMatcher models the matching of a label. Create with NewLabelMatcher.
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type LabelMatcher struct {
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Type MatchType
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Name model.LabelName
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Value model.LabelValue
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re *regexp.Regexp
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score float64 // Cardinality score, between 0 and 1, 0 is lowest cardinality.
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}
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// NewLabelMatcher returns a LabelMatcher object ready to use.
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func NewLabelMatcher(matchType MatchType, name model.LabelName, value model.LabelValue) (*LabelMatcher, error) {
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m := &LabelMatcher{
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Type: matchType,
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Name: name,
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Value: value,
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}
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if matchType == RegexMatch || matchType == RegexNoMatch {
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re, err := regexp.Compile("^(?:" + string(value) + ")$")
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if err != nil {
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return nil, err
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}
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m.re = re
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}
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m.calculateScore()
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return m, nil
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}
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// calculateScore is a helper method only called in the constructor. It
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// calculates the cardinality score upfront, so that sorting by it is faster and
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// doesn't change internal state of the matcher.
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//
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// The score is based on a pretty bad but still quite helpful heuristics for
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// now. Note that this is an interim solution until the work in progress to
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// properly intersect matchers is complete. We intend to not invest any further
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// effort into tweaking the score calculation, as this could easily devolve into
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// a rabbit hole.
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//
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// The heuristics works along the following lines:
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//
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// - A matcher that is known to match nothing would have a score of 0. (This
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// case doesn't happen in the scope of this method.)
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//
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// - A matcher that matches the empty string has a score of 1.
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//
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// - Equal matchers have a score <= 0.5. The order in score for other matchers
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// are RegexMatch, RegexNoMatch, NotEqual.
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//
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// - There are a number of score adjustments for known "magic" parts, like
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// instance labels, metric names containing a colon (which are probably
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// recording rules) and such.
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//
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// - On top, there is a tiny adjustment for the length of the matcher, following
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// the blunt expectation that a long label name and/or value is more specific
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// and will therefore have a lower cardinality.
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//
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// To reiterate on the above: PLEASE RESIST THE TEMPTATION TO TWEAK THIS
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// METHOD. IT IS "MAGIC" ENOUGH ALREADY AND WILL GO AWAY WITH THE UPCOMING MORE
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// POWERFUL INDEXING.
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func (m *LabelMatcher) calculateScore() {
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if m.Match("") {
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m.score = 1
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return
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}
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// lengthCorrection is between 0 (for length 0) and 0.1 (for length +Inf).
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lengthCorrection := 0.1 * (1 - 1/float64(len(m.Name)+len(m.Value)+1))
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switch m.Type {
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case Equal:
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m.score = 0.3 - lengthCorrection
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case RegexMatch:
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m.score = 0.6 - lengthCorrection
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case RegexNoMatch:
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m.score = 0.8 + lengthCorrection
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case NotEqual:
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m.score = 0.9 + lengthCorrection
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}
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if m.Type != Equal {
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// Don't bother anymore in this case.
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return
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}
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switch m.Name {
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case model.InstanceLabel:
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// Matches only metrics from a single instance, which clearly
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// limits the damage.
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m.score -= 0.2
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case model.JobLabel:
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// The usual case is a relatively low number of jobs with many
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// metrics each.
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m.score += 0.1
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case model.BucketLabel, model.QuantileLabel:
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// Magic labels for buckets and quantiles will match copiously.
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m.score += 0.2
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case model.MetricNameLabel:
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if strings.Contains(string(m.Value), ":") {
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// Probably a recording rule with limited cardinality.
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m.score -= 0.1
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return
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}
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if m.Value == "up" || m.Value == "scrape_duration_seconds" {
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// Synthetic metrics which are contained in every scrape
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// exactly once. There might be less frequent metric
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// names, but the worst case is limited here, so give it
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// a bump.
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m.score -= 0.05
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return
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}
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}
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}
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// MatchesEmptyString returns true if the LabelMatcher matches the empty string.
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func (m *LabelMatcher) MatchesEmptyString() bool {
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return m.score >= 1
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}
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func (m *LabelMatcher) String() string {
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return fmt.Sprintf("%s%s%q", m.Name, m.Type, m.Value)
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}
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// Match returns true if the label matcher matches the supplied label value.
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func (m *LabelMatcher) Match(v model.LabelValue) bool {
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switch m.Type {
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case Equal:
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return m.Value == v
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case NotEqual:
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return m.Value != v
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case RegexMatch:
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return m.re.MatchString(string(v))
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case RegexNoMatch:
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return !m.re.MatchString(string(v))
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default:
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panic("invalid match type")
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}
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}
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// Filter takes a list of label values and returns all label values which match
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// the label matcher.
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func (m *LabelMatcher) Filter(in model.LabelValues) model.LabelValues {
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out := model.LabelValues{}
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for _, v := range in {
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if m.Match(v) {
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out = append(out, v)
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}
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}
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return out
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}
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