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The individual strings for label names and values are held in a table, and each Labels value is a run of varint-encoded indexes into that table. When creating new labels, a sync.Mutex is locked around reads and writes. When reading labels, there is no locking because the table of strings used by those labels is immutable. Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
53 lines
1.7 KiB
Go
53 lines
1.7 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 dedupelabels
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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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for pos := 0; pos < len(ls.data); {
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name, newPos := decodeString(ls.syms, ls.data, pos)
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value, newPos := decodeString(ls.syms, ls.data, newPos)
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if len(b)+len(name)+len(value)+2 >= cap(b) {
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// If labels entry is 1KB+, hash the rest of them via Write().
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h := xxhash.New()
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_, _ = h.Write(b)
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for pos < len(ls.data) {
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name, pos = decodeString(ls.syms, ls.data, pos)
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value, pos = decodeString(ls.syms, ls.data, pos)
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_, _ = h.WriteString(name)
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_, _ = h.Write(seps)
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_, _ = h.WriteString(value)
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_, _ = h.Write(seps)
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}
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return h.Sum64()
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}
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b = append(b, name...)
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b = append(b, seps[0])
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b = append(b, value...)
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b = append(b, seps[0])
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pos = newPos
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}
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return xxhash.Sum64(b)
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}
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