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etcdserve: revert the etcdserver side change for the data loss on one node cluster

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Since the raft side change has been merged, so we need to revert the etcdserver
side change.
Refer to
  https://github.com/etcd-io/etcd/pull/14413
  https://github.com/etcd-io/etcd/pull/14400

Signed-off-by: Benjamin Wang <wachao@vmware.com>
This commit is contained in:
Benjamin Wang 2022-09-22 15:19:20 +08:00
parent 997260a832
commit 9097e61b40
2 changed files with 3 additions and 127 deletions
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53
server/etcdserver/raft.go
View File

@ -209,14 +209,6 @@ func (r *raftNode) start(rh *raftReadyHandler) {
updateCommittedIndex(&ap, rh)
waitWALSync := shouldWaitWALSync(rd)
if waitWALSync {
// gofail: var raftBeforeSaveWaitWalSync struct{}
if err := r.storage.Save(rd.HardState, rd.Entries); err != nil {
r.lg.Fatal("failed to save Raft hard state and entries", zap.Error(err))
}
}
select {
case r.applyc <- ap:
case <-r.stopped:
@ -241,11 +233,9 @@ func (r *raftNode) start(rh *raftReadyHandler) {
// gofail: var raftAfterSaveSnap struct{}
}
if !waitWALSync {
// gofail: var raftBeforeSave struct{}
if err := r.storage.Save(rd.HardState, rd.Entries); err != nil {
r.lg.Fatal("failed to save Raft hard state and entries", zap.Error(err))
}
// gofail: var raftBeforeSave struct{}
if err := r.storage.Save(rd.HardState, rd.Entries); err != nil {
r.lg.Fatal("failed to save Raft hard state and entries", zap.Error(err))
}
if !raft.IsEmptyHardState(rd.HardState) {
proposalsCommitted.Set(float64(rd.HardState.Commit))
@ -324,43 +314,6 @@ func (r *raftNode) start(rh *raftReadyHandler) {
}()
}
// For a cluster with only one member, the raft may send both the
// unstable entries and committed entries to etcdserver, and there
// may have overlapped log entries between them.
//
// etcd responds to the client once it finishes (actually partially)
// the applying workflow. But when the client receives the response,
// it doesn't mean etcd has already successfully saved the data,
// including BoltDB and WAL, because:
// 1. etcd commits the boltDB transaction periodically instead of on each request;
// 2. etcd saves WAL entries in parallel with applying the committed entries.
//
// Accordingly, it might run into a situation of data loss when the etcd crashes
// immediately after responding to the client and before the boltDB and WAL
// successfully save the data to disk.
// Note that this issue can only happen for clusters with only one member.
//
// For clusters with multiple members, it isn't an issue, because etcd will
// not commit & apply the data before it being replicated to majority members.
// When the client receives the response, it means the data must have been applied.
// It further means the data must have been committed.
// Note: for clusters with multiple members, the raft will never send identical
// unstable entries and committed entries to etcdserver.
//
// Refer to https://github.com/etcd-io/etcd/issues/14370.
func shouldWaitWALSync(rd raft.Ready) bool {
if len(rd.CommittedEntries) == 0 || len(rd.Entries) == 0 {
return false
}
// Check if there is overlap between unstable and committed entries
// assuming that their index and term are only incrementing.
lastCommittedEntry := rd.CommittedEntries[len(rd.CommittedEntries)-1]
firstUnstableEntry := rd.Entries[0]
return lastCommittedEntry.Term > firstUnstableEntry.Term ||
(lastCommittedEntry.Term == firstUnstableEntry.Term && lastCommittedEntry.Index >= firstUnstableEntry.Index)
}
func updateCommittedIndex(ap *toApply, rh *raftReadyHandler) {
var ci uint64
if len(ap.entries) != 0 {

77
server/etcdserver/raft_test.go
View File

@ -22,7 +22,6 @@ import (
"testing"
"time"
"github.com/stretchr/testify/assert"
"go.etcd.io/etcd/client/pkg/v3/types"
"go.etcd.io/etcd/pkg/v3/pbutil"
"go.etcd.io/etcd/raft/v3"
@ -318,79 +317,3 @@ func TestStopRaftNodeMoreThanOnce(t *testing.T) {
}
}
}
func TestShouldWaitWALSync(t *testing.T) {
testcases := []struct {
name string
unstableEntries []raftpb.Entry
commitedEntries []raftpb.Entry
expectedResult bool
}{
{
name: "both entries are nil",
unstableEntries: nil,
commitedEntries: nil,
expectedResult: false,
},
{
name: "both entries are empty slices",
unstableEntries: []raftpb.Entry{},
commitedEntries: []raftpb.Entry{},
expectedResult: false,
},
{
name: "one nil and the other empty",
unstableEntries: nil,
commitedEntries: []raftpb.Entry{},
expectedResult: false,
},
{
name: "one nil and the other has data",
unstableEntries: nil,
commitedEntries: []raftpb.Entry{{Term: 4, Index: 10, Type: raftpb.EntryNormal, Data: []byte{0x11, 0x22, 0x33}}},
expectedResult: false,
},
{
name: "one empty and the other has data",
unstableEntries: []raftpb.Entry{},
commitedEntries: []raftpb.Entry{{Term: 4, Index: 10, Type: raftpb.EntryNormal, Data: []byte{0x11, 0x22, 0x33}}},
expectedResult: false,
},
{
name: "has different term and index",
unstableEntries: []raftpb.Entry{{Term: 5, Index: 11, Type: raftpb.EntryNormal, Data: []byte{0x11, 0x22, 0x33}}},
commitedEntries: []raftpb.Entry{{Term: 4, Index: 10, Type: raftpb.EntryNormal, Data: []byte{0x11, 0x22, 0x33}}},
expectedResult: false,
},
{
name: "has identical data",
unstableEntries: []raftpb.Entry{{Term: 4, Index: 10, Type: raftpb.EntryNormal, Data: []byte{0x11, 0x22, 0x33}}},
commitedEntries: []raftpb.Entry{{Term: 4, Index: 10, Type: raftpb.EntryNormal, Data: []byte{0x11, 0x22, 0x33}}},
expectedResult: true,
},
{
name: "has overlapped entry",
unstableEntries: []raftpb.Entry{
{Term: 4, Index: 10, Type: raftpb.EntryNormal, Data: []byte{0x11, 0x22, 0x33}},
{Term: 4, Index: 11, Type: raftpb.EntryNormal, Data: []byte{0x44, 0x55, 0x66}},
{Term: 4, Index: 12, Type: raftpb.EntryNormal, Data: []byte{0x77, 0x88, 0x99}},
},
commitedEntries: []raftpb.Entry{
{Term: 4, Index: 8, Type: raftpb.EntryNormal, Data: []byte{0x07, 0x08, 0x09}},
{Term: 4, Index: 9, Type: raftpb.EntryNormal, Data: []byte{0x10, 0x11, 0x12}},
{Term: 4, Index: 10, Type: raftpb.EntryNormal, Data: []byte{0x11, 0x22, 0x33}},
},
expectedResult: true,
},
}
for _, tc := range testcases {
t.Run(tc.name, func(t *testing.T) {
shouldWALSync := shouldWaitWALSync(raft.Ready{
Entries: tc.unstableEntries,
CommittedEntries: tc.commitedEntries,
})
assert.Equal(t, tc.expectedResult, shouldWALSync)
})
}
}