etcd后端存储用的是bolt，在分析完server如何初始化raftNode流程后，我们看下后端存储bolt-db的初始化流程。
在server初始化函数里，有个bootstrap函数server/etcdserver/server.go
代码语言：javascript复制func NewServer(cfg config.ServerConfig) (srv *EtcdServer, err error) {
b, err := bootstrap(cfg)
v2store: b.storage.st,向下跟下它的调用路径server/etcdserver/bootstrap.go
代码语言：javascript复制func bootstrap(cfg config.ServerConfig) (b *bootstrappedServer, err error) {
backend, err := bootstrapBackend(cfg, haveWAL, st, ss)调用了backend包的OpenBackend函数：
代码语言：javascript复制func bootstrapBackend(cfg config.ServerConfig, haveWAL bool, st v2store.Store, ss *snap.Snapshotter) (backend *bootstrappedBackend, err error) {
be := serverstorage.OpenBackend(cfg, beHooks)
return &bootstrappedBackend{
beHooks: beHooks,
be: be,
ci: ci,
beExist: beExist,
snapshot: snapshot,
}, nilserver/storage/backend.go
代码语言：javascript复制func OpenBackend(cfg config.ServerConfig, hooks backend.Hooks) backend.Backend {
go func() {
beOpened <- newBackend(cfg, hooks)
}()
select {
case be := <-beOpened:
return be func newBackend(cfg config.ServerConfig, hooks backend.Hooks) backend.Backend {
return backend.New(bcfg)
该函数同时也被OpenSnapshotBackend调用了
代码语言：javascript复制 func OpenSnapshotBackend(cfg config.ServerConfig, ss *snap.Snapshotter, snapshot raftpb.Snapshot, hooks *BackendHooks) (backend.Backend, error) {
return OpenBackend(cfg, hooks), nil再往下跟一层，终于发现了bolt的初始化函数server/storage/backend/backend.go
代码语言：javascript复制type backend struct {
bopts *bolt.Options
db *bolt.DBfunc newBackend(bcfg BackendConfig) *backend {
bopts := &bolt.Options{}
db, err := bolt.Open(bcfg.Path, 0600, bopts)
go b.run()func (b *backend) defrag() error {
b.db, err = bolt.Open(dbp, 0600, b.bopts)其核心函数是run函数：
代码语言：javascript复制func (b *backend) run() {
for {
select {
case <-t.C:
case <-b.stopc:
b.batchTx.CommitAndStop()
return
}
if b.batchTx.safePending() != 0 {
b.batchTx.Commit()
}
t.Reset(b.batchInterval)
}func (b *backend) begin(write bool) *bolt.Tx {
tx := b.unsafeBegin(write)
db := tx.DB()func New(bcfg BackendConfig) Backend {
return newBackend(bcfg)
}除了核心流程，其它的工具流程也使用了bolt-db比如tools/etcd-dump-db/main.go
代码语言：javascript复制listBucketCommand = &cobra.Command{
Use: "list-bucket [data dir or db file path]",
Short: "bucket lists all buckets.",
Run: listBucketCommandFunc,
}func listBucketCommandFunc(cmd *cobra.Command, args []string) {
bts, err := getBuckets(dp)tools/etcd-dump-db/backend.go
代码语言：javascript复制func getBuckets(dbPath string) (buckets []string, err error) {
db, derr := bolt.Open(dbPath, 0600, &bolt.Options{Timeout: flockTimeout})
err = db.View(func(tx *bolt.Tx) error {
return tx.ForEach(func(b []byte, _ *bolt.Bucket) error {
buckets = append(buckets, string(b))
return nil
})
})etcdutl/snapshot/v3_snapshot.go
代码语言：javascript复制func (s *v3Manager) Status(dbPath string) (ds Status, err error) {
db, err := bolt.Open(dbPath, 0400, &bolt.Options{ReadOnly: true})tools/benchmark/cmd/mvcc.go
代码语言：javascript复制func initMVCC() {
be := backend.New(bcfg)bolt作为etcd后端的kv存储，可以持久化，支持事务mvcc，从而保证了etcd的存储的可靠性。获取到bolt的实例后，会在etcdserver的初始化函数里，将它传递给mvcc
代码语言：javascript复制func NewServer(cfg config.ServerConfig) (srv *EtcdServer, err error) {
srv.kv = mvcc.New(srv.Logger(), srv.be, srv.lessor, mvccStoreConfig)调用的是server/storage/mvcc/watchable_store.go的New方法，并将bolt对象传入
代码语言：javascript复制func New(lg *zap.Logger, b backend.Backend, le lease.Lessor, cfg StoreConfig) WatchableKV {
return newWatchableStore(lg, b, le, cfg)
}func newWatchableStore(lg *zap.Logger, b backend.Backend, le lease.Lessor, cfg StoreConfig) *watchableStore {
s := &watchableStore{
store: NewStore(lg, b, le, cfg),
s.wg.Add(2)
go s.syncWatchersLoop()
go s.syncVictimsLoop()server/storage/mvcc/kvstore.go
代码语言：javascript复制func NewStore(lg *zap.Logger, b backend.Backend, le lease.Lessor, cfg StoreConfig) *store {
s := &store{
cfg: cfg,
b: b,
kvindex: newTreeIndex(lg),
le: le,
currentRev: 1,
compactMainRev: -1,
fifoSched: schedule.NewFIFOScheduler(lg),
stopc: make(chan struct{}),
lg: lg,
}
至此完成了mvcc的初始化
