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113 lines
3.9 KiB
113 lines
3.9 KiB
// Copyright 2017 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 storage
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import (
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"sync"
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"github.com/prometheus/prometheus/pkg/labels"
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)
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// secondaryQuerier is a wrapper that allows a querier to be treated in a best effort manner.
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// This means that an error on any method returned by Querier except Close will be returned as a warning,
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// and the result will be empty.
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//
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// Additionally, Querier ensures that if ANY SeriesSet returned by this querier's Select failed on an initial Next,
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// All other SeriesSet will be return no response as well. This ensures consistent partial response strategy, where you
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// have either full results or none from each secondary Querier.
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// NOTE: This works well only for implementations that only fail during first Next() (e.g fetch from network). If implementation fails
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// during further iterations, set will panic. If Select is invoked after first Next of any returned SeriesSet, querier will panic.
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//
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// Not go-routine safe.
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// NOTE: Prometheus treats all remote storages as secondary / best effort.
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type secondaryQuerier struct {
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genericQuerier
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once sync.Once
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done bool
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asyncSets []genericSeriesSet
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}
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func newSecondaryQuerierFrom(q Querier) genericQuerier {
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return &secondaryQuerier{genericQuerier: newGenericQuerierFrom(q)}
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}
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func newSecondaryQuerierFromChunk(cq ChunkQuerier) genericQuerier {
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return &secondaryQuerier{genericQuerier: newGenericQuerierFromChunk(cq)}
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}
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func (s *secondaryQuerier) LabelValues(name string) ([]string, Warnings, error) {
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vals, w, err := s.genericQuerier.LabelValues(name)
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if err != nil {
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return nil, append([]error{err}, w...), nil
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}
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return vals, w, nil
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}
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func (s *secondaryQuerier) LabelNames() ([]string, Warnings, error) {
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names, w, err := s.genericQuerier.LabelNames()
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if err != nil {
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return nil, append([]error{err}, w...), nil
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}
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return names, w, nil
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}
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func (s *secondaryQuerier) createFn(asyncSet genericSeriesSet) func() (genericSeriesSet, bool) {
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s.asyncSets = append(s.asyncSets, asyncSet)
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curr := len(s.asyncSets) - 1
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return func() (genericSeriesSet, bool) {
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s.once.Do(func() {
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// At first create invocation we iterate over all sets and ensure its Next() returns some value without
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// errors. This is to ensure we support consistent partial failures.
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for i, set := range s.asyncSets {
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if set.Next() {
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continue
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}
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ws := set.Warnings()
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// Failed set.
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if err := set.Err(); err != nil {
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ws = append([]error{err}, ws...)
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// Promote the warnings to the current one.
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s.asyncSets[curr] = warningsOnlySeriesSet(ws)
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// One of the sets failed, ensure rest of the sets returns nothing. (All or nothing logic).
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for i := range s.asyncSets {
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if curr != i {
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s.asyncSets[i] = noopGenericSeriesSet{}
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}
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}
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break
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}
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// Exhausted set.
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s.asyncSets[i] = warningsOnlySeriesSet(ws)
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}
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s.done = true
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})
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switch s.asyncSets[curr].(type) {
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case warningsOnlySeriesSet, noopGenericSeriesSet:
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return s.asyncSets[curr], false
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default:
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return s.asyncSets[curr], true
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}
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}
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}
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func (s *secondaryQuerier) Select(sortSeries bool, hints *SelectHints, matchers ...*labels.Matcher) genericSeriesSet {
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if s.done {
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panic("secondaryQuerier: Select invoked after first Next of any returned SeriesSet was done")
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}
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return &lazySeriesSet{create: s.createFn(s.genericQuerier.Select(sortSeries, hints, matchers...))}
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}
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