diff --git a/storage/fanout.go b/storage/fanout.go index 2bc4323a7..62f973044 100644 --- a/storage/fanout.go +++ b/storage/fanout.go @@ -63,27 +63,26 @@ func (f *fanout) StartTime() (int64, error) { } func (f *fanout) Querier(ctx context.Context, mint, maxt int64) (Querier, error) { - queriers := mergeQuerier{ - queriers: make([]Querier, 0, 1+len(f.secondaries)), - } + queriers := make([]Querier, 0, 1+len(f.secondaries)) // Add primary querier querier, err := f.primary.Querier(ctx, mint, maxt) if err != nil { return nil, err } - queriers.queriers = append(queriers.queriers, querier) + queriers = append(queriers, querier) // Add secondary queriers for _, storage := range f.secondaries { querier, err := storage.Querier(ctx, mint, maxt) if err != nil { - queriers.Close() + NewMergeQuerier(queriers).Close() return nil, err } - queriers.queriers = append(queriers.queriers, querier) + queriers = append(queriers, querier) } - return &queriers, nil + + return NewMergeQuerier(queriers), nil } func (f *fanout) Appender() (Appender, error) { @@ -193,9 +192,26 @@ type mergeQuerier struct { } // NewMergeQuerier returns a new Querier that merges results of input queriers. +// NB NewMergeQuerier will return NoopQuerier if no queriers are passed to it, +// and will filter NoopQueriers from its arguments, in order to reduce overhead +// when only one querier is passed. func NewMergeQuerier(queriers []Querier) Querier { - return &mergeQuerier{ - queriers: queriers, + filtered := make([]Querier, 0, len(queriers)) + for _, querier := range queriers { + if querier != NoopQuerier() { + filtered = append(filtered, querier) + } + } + + switch len(filtered) { + case 0: + return NoopQuerier() + case 1: + return filtered[0] + default: + return &mergeQuerier{ + queriers: filtered, + } } } diff --git a/storage/noop.go b/storage/noop.go new file mode 100644 index 000000000..358cf2611 --- /dev/null +++ b/storage/noop.go @@ -0,0 +1,54 @@ +// 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 storage + +import "github.com/prometheus/prometheus/pkg/labels" + +type noopQuerier struct{} + +// NoopQuerier is a Querier that does nothing. +func NoopQuerier() Querier { + return noopQuerier{} +} + +func (noopQuerier) Select(...*labels.Matcher) SeriesSet { + return NoopSeriesSet() +} + +func (noopQuerier) LabelValues(name string) ([]string, error) { + return nil, nil +} + +func (noopQuerier) Close() error { + return nil +} + +type noopSeriesSet struct{} + +// NoopSeriesSet is a SeriesSet that does nothing. +func NoopSeriesSet() SeriesSet { + return noopSeriesSet{} +} + +func (noopSeriesSet) Next() bool { + return false +} + +func (noopSeriesSet) At() Series { + return nil +} + +func (noopSeriesSet) Err() error { + return nil +}