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// Copyright 2022 The etcd 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 mvcc
import (
"hash"
"hash/crc32"
"sort"
"sync"
"go.etcd.io/etcd/server/v3/mvcc/backend"
"go.etcd.io/etcd/server/v3/mvcc/buckets"
"go.uber.org/zap"
)
const (
hashStorageMaxSize = 10
)
func unsafeHashByRev(tx backend.ReadTx, compactRevision, revision int64, keep map[revision]struct{}) (KeyValueHash, error) {
h := newKVHasher(compactRevision, revision, keep)
err := tx.UnsafeForEach(buckets.Key, func(k, v []byte) error {
h.WriteKeyValue(k, v)
return nil
})
return h.Hash(), err
}
type kvHasher struct {
hash hash.Hash32
compactRevision int64
revision int64
keep map[revision]struct{}
}
func newKVHasher(compactRev, rev int64, keep map[revision]struct{}) kvHasher {
h := crc32.New(crc32.MakeTable(crc32.Castagnoli))
h.Write(buckets.Key.Name())
return kvHasher{
hash: h,
compactRevision: compactRev,
revision: rev,
keep: keep,
}
}
func (h *kvHasher) WriteKeyValue(k, v []byte) {
kr := bytesToRev(k)
upper := revision{main: h.revision + 1}
if !upper.GreaterThan(kr) {
return
}
isTombstoneRev := isTombstone(k)
lower := revision{main: h.compactRevision + 1}
// skip revisions that are scheduled for deletion
// due to compacting; don't skip if there isn't one.
if lower.GreaterThan(kr) && len(h.keep) > 0 {
if _, ok := h.keep[kr]; !ok {
return
}
}
// When performing compaction, if the compacted revision is a
// tombstone, older versions (<= 3.5.15 or <= 3.4.33) will delete
// the tombstone. But newer versions (> 3.5.15 or > 3.4.33) won't
// delete it. So we should skip the tombstone in such cases when
// computing the hash to ensure that both older and newer versions
// can always generate the same hash values.
if kr.main == h.compactRevision && isTombstoneRev {
return
}
h.hash.Write(k)
h.hash.Write(v)
}
func (h *kvHasher) Hash() KeyValueHash {
return KeyValueHash{Hash: h.hash.Sum32(), CompactRevision: h.compactRevision, Revision: h.revision}
}
type KeyValueHash struct {
Hash uint32
CompactRevision int64
Revision int64
}
type HashStorage interface {
// Hash computes the hash of the KV's backend.
Hash() (hash uint32, revision int64, err error)
// HashByRev computes the hash of all MVCC revisions up to a given revision.
HashByRev(rev int64) (hash KeyValueHash, currentRev int64, err error)
// Store adds hash value in local cache, allowing it can be returned by HashByRev.
Store(valueHash KeyValueHash)
// Hashes returns list of up to `hashStorageMaxSize` newest previously stored hashes.
Hashes() []KeyValueHash
}
type hashStorage struct {
store *store
hashMu sync.RWMutex
hashes []KeyValueHash
lg *zap.Logger
}
func newHashStorage(lg *zap.Logger, s *store) *hashStorage {
return &hashStorage{
store: s,
lg: lg,
}
}
func (s *hashStorage) Hash() (hash uint32, revision int64, err error) {
return s.store.hash()
}
func (s *hashStorage) HashByRev(rev int64) (KeyValueHash, int64, error) {
s.hashMu.RLock()
for _, h := range s.hashes {
if rev == h.Revision {
s.hashMu.RUnlock()
s.store.revMu.RLock()
currentRev := s.store.currentRev
s.store.revMu.RUnlock()
return h, currentRev, nil
}
}
s.hashMu.RUnlock()
return s.store.hashByRev(rev)
}
func (s *hashStorage) Store(hash KeyValueHash) {
s.lg.Info("storing new hash",
zap.Uint32("hash", hash.Hash),
zap.Int64("revision", hash.Revision),
zap.Int64("compact-revision", hash.CompactRevision),
)
s.hashMu.Lock()
defer s.hashMu.Unlock()
s.hashes = append(s.hashes, hash)
sort.Slice(s.hashes, func(i, j int) bool {
return s.hashes[i].Revision < s.hashes[j].Revision
})
if len(s.hashes) > hashStorageMaxSize {
s.hashes = s.hashes[len(s.hashes)-hashStorageMaxSize:]
}
}
func (s *hashStorage) Hashes() []KeyValueHash {
s.hashMu.RLock()
// Copy out hashes under lock just to be safe
hashes := make([]KeyValueHash, 0, len(s.hashes))
for _, hash := range s.hashes {
hashes = append(hashes, hash)
}
s.hashMu.RUnlock()
return hashes
}
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