mirror of https://github.com/prometheus/prometheus
55 lines
1.6 KiB
Go
55 lines
1.6 KiB
Go
// Copyright 2020 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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//go:build stringlabels
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package labels
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import (
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"github.com/cespare/xxhash/v2"
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)
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// StableHash is a labels hashing implementation which is guaranteed to not change over time.
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// This function should be used whenever labels hashing backward compatibility must be guaranteed.
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func StableHash(ls Labels) uint64 {
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// Use xxhash.Sum64(b) for fast path as it's faster.
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b := make([]byte, 0, 1024)
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var h *xxhash.Digest
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for i := 0; i < len(ls.data); {
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var v Label
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v.Name, i = decodeString(ls.data, i)
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v.Value, i = decodeString(ls.data, i)
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if h == nil && len(b)+len(v.Name)+len(v.Value)+2 >= cap(b) {
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// If labels entry is 1KB+, switch to Write API. Copy in the values up to this point.
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h = xxhash.New()
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_, _ = h.Write(b)
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}
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if h != nil {
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_, _ = h.WriteString(v.Name)
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_, _ = h.Write(seps)
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_, _ = h.WriteString(v.Value)
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_, _ = h.Write(seps)
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continue
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}
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b = append(b, v.Name...)
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b = append(b, sep)
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b = append(b, v.Value...)
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b = append(b, sep)
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}
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if h != nil {
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return h.Sum64()
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}
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return xxhash.Sum64(b)
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}
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