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[WIP] *: support online downgrade from 3.5 to 3.4 #15990

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[WIP] *: support online downgrade from 3.5 to 3.4 #15990

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2 changes: 2 additions & 0 deletions etcdserver/api/capability.go
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,8 @@ var (
"3.2.0": {AuthCapability: true, V3rpcCapability: true},
"3.3.0": {AuthCapability: true, V3rpcCapability: true},
"3.4.0": {AuthCapability: true, V3rpcCapability: true},
//TODO: use EnableCapability and flag to control this dynamically
"3.5.0": {AuthCapability: true, V3rpcCapability: true},
}

enableMapMu sync.RWMutex
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6 changes: 4 additions & 2 deletions etcdserver/api/membership/cluster.go
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Original file line number Diff line number Diff line change
Expand Up @@ -248,7 +248,8 @@ func (c *RaftCluster) Recover(onSet func(*zap.Logger, *semver.Version)) {

c.members, c.removed = membersFromStore(c.lg, c.v2store)
c.version = clusterVersionFromStore(c.lg, c.v2store)
mustDetectDowngrade(c.lg, c.version)
// TODO: add flag to control this check
//mustDetectDowngrade(c.lg, c.version)
onSet(c.lg, c.version)

for _, m := range c.members {
Expand Down Expand Up @@ -567,7 +568,8 @@ func (c *RaftCluster) SetVersion(ver *semver.Version, onSet func(*zap.Logger, *s
}
oldVer := c.version
c.version = ver
mustDetectDowngrade(c.lg, c.version)
// TODO: add flag to control this check
//mustDetectDowngrade(c.lg, c.version)
if c.v2store != nil {
mustSaveClusterVersionToStore(c.v2store, ver)
}
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15 changes: 15 additions & 0 deletions mvcc/kvstore.go
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,10 @@ var (
scheduledCompactKeyName = []byte("scheduledCompactRev")
finishedCompactKeyName = []byte("finishedCompactRev")

// 3.5 meta keys that have to be deleted for downgrade
confStateKeyName = []byte("confState")
termKeyName = []byte("term")

ErrCompacted = errors.New("mvcc: required revision has been compacted")
ErrFutureRev = errors.New("mvcc: required revision is a future revision")
ErrCanceled = errors.New("mvcc: watcher is canceled")
Expand Down Expand Up @@ -148,6 +152,8 @@ func NewStore(lg *zap.Logger, b backend.Backend, le lease.Lessor, ig ConsistentI
tx.Lock()
tx.UnsafeCreateBucket(keyBucketName)
tx.UnsafeCreateBucket(metaBucketName)
// TODO: add flag to control this
downgradeMetaBucket(tx)
tx.Unlock()
s.b.ForceCommit()

Expand Down Expand Up @@ -379,6 +385,9 @@ func (s *store) restore() error {
tx := s.b.BatchTx()
tx.Lock()

// TODO: add flag to control this
downgradeMetaBucket(tx)

_, finishedCompactBytes := tx.UnsafeRange(metaBucketName, finishedCompactKeyName, nil, 0)
if len(finishedCompactBytes) != 0 {
s.revMu.Lock()
Expand Down Expand Up @@ -637,3 +646,9 @@ func appendMarkTombstone(lg *zap.Logger, b []byte) []byte {
func isTombstone(b []byte) bool {
return len(b) == markedRevBytesLen && b[markBytePosition] == markTombstone
}

// downgradeMetaBucket delete 3.5 specific keys to make backend fully compatible with 3.4
func downgradeMetaBucket(tx backend.BatchTx) {
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I think this part can be done using capabilities of new migrate command from 3.6, cc @serathius

tx.UnsafeDelete(metaBucketName, confStateKeyName)
tx.UnsafeDelete(metaBucketName, termKeyName)
}
2 changes: 2 additions & 0 deletions mvcc/kvstore_test.go
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Expand Up @@ -397,6 +397,8 @@ func TestStoreRestore(t *testing.T) {
t.Errorf("current rev = %v, want 5", s.currentRev)
}
wact := []testutil.Action{
{Name: "delete", Params: []interface{}{metaBucketName, confStateKeyName}},
{Name: "delete", Params: []interface{}{metaBucketName, termKeyName}},
{Name: "range", Params: []interface{}{metaBucketName, finishedCompactKeyName, []byte(nil), int64(0)}},
{Name: "range", Params: []interface{}{metaBucketName, scheduledCompactKeyName, []byte(nil), int64(0)}},
{Name: "range", Params: []interface{}{keyBucketName, newTestRevBytes(revision{1, 0}), newTestRevBytes(revision{math.MaxInt64, math.MaxInt64}), int64(restoreChunkKeys)}},
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