prometheus/model/labels/sharding_stringlabels.go

55 lines
1.6 KiB
Go

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