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storage: delete all "raft log as part of snapshots" code
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Raft log entries are no longer sent along with snapshots as of v19.2
(more specifically, #35701), we can/should delete all code around the
sending/handling of log entries in snapshots before v20.1 is cut. This
simplifies a few snapshot related protos and naturally obviates the need
to handle sideloaded proposals within snapshots.

Release note: None
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@irfansharif
irfansharif committed Jan 30, 2020
1 parent c434a8d commit 8d2f75e
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Showing 7 changed files with 131 additions and 808 deletions.
276 changes: 94 additions & 182 deletions pkg/storage/raft.pb.go
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18 changes: 3 additions & 15 deletions pkg/storage/raft.proto
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Original file line number Diff line number Diff line change
Expand Up @@ -164,29 +164,17 @@ message SnapshotRequest {
// The type of the snapshot.
optional Type type = 9 [(gogoproto.nullable) = false];

// Whether the snapshot uses the unreplicated RaftTruncatedState or not.
// This is generally always true at 2.2 and above outside of the migration
// phase, though theoretically it could take a long time for all ranges
// to update to the new mechanism. This bool is true iff the Raft log at
// the snapshot's applied index is using the new key. In particular, it
// is true if the index itself carries out the migration (in which case
// the data in the snapshot contains neither key).
//
// See VersionUnreplicatedRaftTruncatedState.
optional bool unreplicated_truncated_state = 8 [(gogoproto.nullable) = false];
reserved 8;
}

optional Header header = 1;

// A RocksDB BatchRepr. Multiple kv_batches may be sent across multiple request messages.
optional bytes kv_batch = 2 [(gogoproto.customname) = "KVBatch"];

// These are really raftpb.Entry, but we model them as raw bytes to avoid
// roundtripping through memory. They are separate from the kv_batch to
// allow flexibility in log implementations.
repeated bytes log_entries = 3;

optional bool final = 4 [(gogoproto.nullable) = false];

reserved 3;
}

message SnapshotResponse {
Expand Down
78 changes: 18 additions & 60 deletions pkg/storage/replica_command.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1836,9 +1836,9 @@ func execChangeReplicasTxn(
// returns true, this is communicated back to the sender, which then proceeds to
// call `kvBatchSnapshotStrategy.Send`. This uses the iterator captured earlier
// to send the data in chunks, each chunk a streaming grpc message. The sender
// then sends a final message with an indicaton that it's done and blocks again,
// waiting for a second and final response from the recipient which indicates if
// the snapshot was a success.
// then sends a final message with an indication that it's done and blocks
// again, waiting for a second and final response from the recipient which
// indicates if the snapshot was a success.
//
// `receiveSnapshot` takes the key-value pairs sent and incrementally creates
// three SSTs from them for direct ingestion: one for the replicated range-ID
Expand All @@ -1857,13 +1857,13 @@ func execChangeReplicasTxn(
// snapshot* message is manually handed to the replica's Raft node (by calling
// `stepRaftGroup` + `handleRaftReadyRaftMuLocked`). During the application
// process, several other SSTs may be created for direct ingestion. An SST for
// the unreplicated range-ID local keys is created for the Raft entries, hard
// state, and truncated state. An SST is created for deleting each subsumed
// replica's range-ID local keys and at most two SSTs are created for deleting
// the user keys and range local keys of all subsumed replicas. All in all, a
// maximum of 6 + SR SSTs will be created for direct ingestion where SR is the
// number of subsumed replicas. In the case where there are no subsumed
// replicas, 4 SSTs will be created.
// the unreplicated range-ID local keys is created for the hard state and
// truncated state. An SST is created for deleting each subsumed replica's
// range-ID local keys and at most two SSTs are created for deleting the user
// keys and range local keys of all subsumed replicas. All in all, a maximum of
// 6 + SR SSTs will be created for direct ingestion where SR is the number of
// subsumed replicas. In the case where there are no subsumed replicas, 4 SSTs
// will be created.
//
// [1]: There is a third kind of snapshot, called "preemptive", which is how we
// avoided the above fragility before learner replicas were introduced in the
Expand Down Expand Up @@ -1922,42 +1922,16 @@ func (r *Replica) sendSnapshot(
return &benignError{errors.New("raft status not initialized")}
}

usesReplicatedTruncatedState, err := engine.MVCCGetProto(
ctx, snap.EngineSnap, keys.RaftTruncatedStateLegacyKey(r.RangeID), hlc.Timestamp{}, nil, engine.MVCCGetOptions{},
)
if err != nil {
return errors.Wrap(err, "loading legacy truncated state")
}

canAvoidSendingLog := !usesReplicatedTruncatedState &&
snap.State.TruncatedState.Index < snap.State.RaftAppliedIndex

if canAvoidSendingLog {
// If we're not using a legacy (replicated) truncated state, we avoid
// sending the (past) Raft log in the snapshot in the first place and
// send only those entries that are actually useful to the follower.
// This is done by changing the truncated state, which we're allowed
// to do since it is not a replicated key (and thus not subject to
// matching across replicas). The actual sending happens here:
_ = (*kvBatchSnapshotStrategy)(nil).Send
// and results in no log entries being sent at all. Note that
// Metadata.Index is really the applied index of the replica.
snap.State.TruncatedState = &roachpb.RaftTruncatedState{
Index: snap.RaftSnap.Metadata.Index,
Term: snap.RaftSnap.Metadata.Term,
}
// We update the ReplicaState in the snapshot to match the snapshot metadata
// provided to use by etcd/raft.
metadata := snap.RaftSnap.Metadata
snap.State.TruncatedState = &roachpb.RaftTruncatedState{
Index: metadata.Index,
Term: metadata.Term,
}

req := SnapshotRequest_Header{
State: snap.State,
// Tell the recipient whether it needs to synthesize the new
// unreplicated TruncatedState. It could tell by itself by peeking into
// the data, but it uses a write only batch for performance which
// doesn't support that; this is easier. Notably, this is true if the
// snap index itself is the one at which the migration happens.
//
// See VersionUnreplicatedRaftTruncatedState.
UnreplicatedTruncatedState: !usesReplicatedTruncatedState,
RaftMessageRequest: RaftMessageRequest{
RangeID: r.RangeID,
FromReplica: sender,
Expand All @@ -1980,25 +1954,9 @@ func (r *Replica) sendSnapshot(
sent := func() {
r.store.metrics.RangeSnapshotsGenerated.Inc(1)
}
if err := r.store.cfg.Transport.SendSnapshot(
ctx,
&r.store.cfg.RaftConfig,
r.store.allocator.storePool,
req,
snap,
r.store.Engine().NewBatch,
sent,
if err := r.store.cfg.Transport.SendSnapshot(ctx, &r.store.cfg.RaftConfig,
r.store.allocator.storePool, req, snap, r.store.Engine().NewBatch, sent,
); err != nil {
if errors.Cause(err) == errMalformedSnapshot {
tag := fmt.Sprintf("r%d_%s", r.RangeID, snap.SnapUUID.Short())
if dir, err := r.store.checkpoint(ctx, tag); err != nil {
log.Warningf(ctx, "unable to create checkpoint %s: %+v", dir, err)
} else {
log.Warningf(ctx, "created checkpoint %s", dir)
}

log.Fatal(ctx, "malformed snapshot generated")
}
return &snapshotError{err}
}
return nil
Expand Down
103 changes: 10 additions & 93 deletions pkg/storage/replica_raftstorage.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -415,20 +415,12 @@ func (r *Replica) GetSnapshot(

log.Eventf(ctx, "new engine snapshot for replica %s", r)

// Delegate to a static function to make sure that we do not depend
// on any indirect calls to r.store.Engine() (or other in-memory
// state of the Replica). Everything must come from the snapshot.
withSideloaded := func(fn func(SideloadStorage) error) error {
r.raftMu.Lock()
defer r.raftMu.Unlock()
return fn(r.raftMu.sideloaded)
}
// NB: We have Replica.mu read-locked, but we need it write-locked in order
// to use Replica.mu.stateLoader. This call is not performance sensitive, so
// create a new state loader.
snapData, err := snapshot(
ctx, snapUUID, stateloader.Make(rangeID), snapType,
snap, rangeID, r.store.raftEntryCache, withSideloaded, startKey,
snap, rangeID, r.store.raftEntryCache, startKey,
)
if err != nil {
log.Errorf(ctx, "error generating snapshot: %+v", err)
Expand All @@ -445,17 +437,10 @@ type OutgoingSnapshot struct {
SnapUUID uuid.UUID
// The Raft snapshot message to send. Contains SnapUUID as its data.
RaftSnap raftpb.Snapshot
// The RocksDB snapshot that will be streamed from.
EngineSnap engine.Reader
// The complete range iterator for the snapshot to stream.
Iter *rditer.ReplicaDataIterator
// The replica state within the snapshot.
State storagepb.ReplicaState
// Allows access the the original Replica's sideloaded storage. Note that
// this isn't a snapshot of the sideloaded storage congruent with EngineSnap
// or RaftSnap -- a log truncation could have removed files from the
// sideloaded storage in the meantime.
WithSideloaded func(func(SideloadStorage) error) error
RaftEntryCache *raftentry.Cache
snapType SnapshotRequest_Type
onClose func()
Expand All @@ -468,7 +453,6 @@ func (s *OutgoingSnapshot) String() string {
// Close releases the resources associated with the snapshot.
func (s *OutgoingSnapshot) Close() {
s.Iter.Close()
s.EngineSnap.Close()
if s.onClose != nil {
s.onClose()
}
Expand All @@ -479,19 +463,8 @@ type IncomingSnapshot struct {
SnapUUID uuid.UUID
// The storage interface for the underlying SSTs.
SSTStorageScratch *SSTSnapshotStorageScratch
// The Raft log entries for this snapshot.
LogEntries [][]byte
// The replica state at the time the snapshot was generated (never nil).
State *storagepb.ReplicaState
//
// When true, this snapshot contains an unreplicated TruncatedState. When
// false, the TruncatedState is replicated (see the reference below) and the
// recipient must avoid also writing the unreplicated TruncatedState. The
// migration to an unreplicated TruncatedState will be carried out during
// the next log truncation (assuming cluster version is bumped at that
// point).
// See the comment on VersionUnreplicatedRaftTruncatedState for details.
UsesUnreplicatedTruncatedState bool
snapType SnapshotRequest_Type
}

Expand All @@ -509,7 +482,6 @@ func snapshot(
snap engine.Reader,
rangeID roachpb.RangeID,
eCache *raftentry.Cache,
withSideloaded func(func(SideloadStorage) error) error,
startKey roachpb.RKey,
) (OutgoingSnapshot, error) {
var desc roachpb.RangeDescriptor
Expand Down Expand Up @@ -549,8 +521,6 @@ func snapshot(

return OutgoingSnapshot{
RaftEntryCache: eCache,
WithSideloaded: withSideloaded,
EngineSnap: snap,
Iter: iter,
State: state,
SnapUUID: snapUUID,
Expand Down Expand Up @@ -738,10 +708,6 @@ func (r *Replica) applySnapshot(
log.Fatalf(ctx, "unexpected range ID %d", s.Desc.RangeID)
}

r.mu.RLock()
replicaID := r.mu.replicaID
r.mu.RUnlock()

snapType := inSnap.snapType
defer func() {
if err == nil {
Expand Down Expand Up @@ -827,44 +793,13 @@ func (r *Replica) applySnapshot(
}

// Update Raft entries.
var lastTerm uint64
var raftLogSize int64
if len(inSnap.LogEntries) > 0 {
logEntries := make([]raftpb.Entry, len(inSnap.LogEntries))
for i, bytes := range inSnap.LogEntries {
if err := protoutil.Unmarshal(bytes, &logEntries[i]); err != nil {
return err
}
}
// If this replica doesn't know its ReplicaID yet, we're applying a
// preemptive snapshot. In this case, we're going to have to write the
// sideloaded proposals into the Raft log. Otherwise, sideload.
if replicaID != 0 {
var err error
var sideloadedEntriesSize int64
logEntries, sideloadedEntriesSize, err = r.maybeSideloadEntriesRaftMuLocked(ctx, logEntries)
if err != nil {
return err
}
raftLogSize += sideloadedEntriesSize
}
var err error
_, lastTerm, raftLogSize, err = r.append(ctx, &unreplicatedSST, 0, invalidLastTerm, raftLogSize, logEntries)
if err != nil {
return err
}
} else {
lastTerm = invalidLastTerm
}
var lastTerm uint64 = invalidLastTerm
r.store.raftEntryCache.Drop(r.RangeID)

// Update TruncatedState if it is unreplicated.
if inSnap.UsesUnreplicatedTruncatedState {
if err := r.raftMu.stateLoader.SetRaftTruncatedState(
ctx, &unreplicatedSST, s.TruncatedState,
); err != nil {
return errors.Wrapf(err, "unable to write UnreplicatedTruncatedState to unreplicated SST writer")
}
if err := r.raftMu.stateLoader.SetRaftTruncatedState(
ctx, &unreplicatedSST, s.TruncatedState,
); err != nil {
return errors.Wrapf(err, "unable to write UnreplicatedTruncatedState to unreplicated SST writer")
}

if err := unreplicatedSST.Finish(); err != nil {
Expand All @@ -877,32 +812,15 @@ func (r *Replica) applySnapshot(
return err
}
}

if s.TruncatedState.Index != snap.Metadata.Index {
log.Fatalf(ctx, "snapshot TruncatedState index %d doesn't match its metadata index %d",
s.TruncatedState.Index, snap.Metadata.Index)
}
if s.RaftAppliedIndex != snap.Metadata.Index {
log.Fatalf(ctx, "snapshot RaftAppliedIndex %d doesn't match its metadata index %d",
s.RaftAppliedIndex, snap.Metadata.Index)
}

if expLen := s.RaftAppliedIndex - s.TruncatedState.Index; expLen != uint64(len(inSnap.LogEntries)) {
entriesRange, err := extractRangeFromEntries(inSnap.LogEntries)
if err != nil {
return err
}

tag := fmt.Sprintf("r%d_%s", r.RangeID, inSnap.SnapUUID.String())
dir, err := r.store.checkpoint(ctx, tag)
if err != nil {
log.Warningf(ctx, "unable to create checkpoint %s: %+v", dir, err)
} else {
log.Warningf(ctx, "created checkpoint %s", dir)
}

log.Fatalf(ctx, "missing log entries in snapshot (%s): got %d entries, expected %d "+
"(TruncatedState.Index=%d, HardState=%s, LogEntries=%s)",
inSnap.String(), len(inSnap.LogEntries), expLen, s.TruncatedState.Index,
hs.String(), entriesRange)
}

// If we're subsuming a replica below, we don't have its last NextReplicaID,
// nor can we obtain it. That's OK: we can just be conservative and use the
// maximum possible replica ID. preDestroyRaftMuLocked will write a replica
Expand Down Expand Up @@ -962,7 +880,6 @@ func (r *Replica) applySnapshot(
// raftpb.SnapshotMetadata.
r.mu.lastIndex = s.RaftAppliedIndex
r.mu.lastTerm = lastTerm
r.mu.raftLogSize = raftLogSize
// Update the store stats for the data in the snapshot.
r.store.metrics.subtractMVCCStats(*r.mu.state.Stats)
r.store.metrics.addMVCCStats(*s.Stats)
Expand Down
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