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54 lines
1.6 KiB
54 lines
1.6 KiB
// 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, seps[0]) |
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b = append(b, v.Value...) |
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b = append(b, seps[0]) |
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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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