etcd now compact raft storage asynchronously, and append entry to raft
storage may happen at the same time. Add the lock to fix the bug that
the entries saved in storage may be organized in a wrong way.
limit the max size of entries sent per message.
Lower the cost at probing state as we limit the size per message;
lower the penalty when aggressively decrease to a too low next.
This panic can never be reached when using raft.Node, because we only
read from propc when there is a leader. However, it is possible to see
this error when using raft the raft object directly (as in MultiNode),
and in this case it is better to simply drop the proposal (as if we had
sent it to a leader that immediately vanished).
Add an error return to MemoryStorage.Append for consistency.
Memory storage should append all entries that have greater index
than the snap.Matedata.Index. We first truncate the old parts of
incoming entries. Then truncate the existing entries in the storage.
At last, we append the incoming entries to the existing entries.
Compaction is now treated as an implementation detail of Storage
implementations; Node.Compact() and related functionality have been
removed. Ready.Snapshot is now used only for incoming snapshots.
A return value has been added to ApplyConfChange to allow applications
to track the node information that must be stored in the snapshot.
raftpb.Snapshot has been split into Snapshot and SnapshotMetadata, to
allow the full snapshot data to be read from disk only when needed.
raft.Storage has new methods Snapshot, ApplySnapshot, HardState, and
SetHardState. The Snapshot and HardState parameters have been removed
from RestartNode() and will now be loaded from Storage instead.
The only remaining difference between StartNode and RestartNode is that
the former bootstraps an initial list of Peers.
The first entry in the log is a dummy which is used for matchTerm
but may not have an actual payload. This change permits Storage
implementations to treat this term value specially instead of
storing it as a dummy Entry.
Storage.FirstIndex() no longer includes the term-only entry.
This reverses a recent decision to create entry zero as initially
unstable; Storage implementations are now required to make
Term(0) == 0 and the first unstable entry is now index 1.
stableTo(0) is no longer allowed.
This entry is now persisted through the normal flow instead of appearing
in the stored log at creation time. This is how things worked before
the Storage interface was introduced. (see coreos/etcd#1689)
Callers must in general have a reference to their Storage objects to
transfer entries from Ready to Storage, so it doesn't make sense to
create a hidden Storage for them.
By explicitly creating Storage objects in tests we can remove a
few casts of raftLog's storage field.
This change splits the raftLog.entries array into an in-memory
"unstable" list and a pluggable interface for retrieving entries that
have been persisted to disk. An in-memory implementation of this
interface is provided which behaves the same as the old version;
in a future commit etcdserver could replace the MemoryStorage with
one backed by the WAL.
