entries,
FollowerLogInformation followerLogInformation) {
// In certain cases outlined below we don't want to send the actual commit index to prevent the follower from
// possibly committing and applying conflicting entries (those with same index, different term) from a prior
// term that weren't replicated to a majority, which would be a violation of raft.
// - if the follower isn't active. In this case we don't know the state of the follower and we send an
// empty AppendEntries as a heart beat to prevent election.
// - if we're in the process of installing a snapshot. In this case we don't send any new entries but still
// need to send AppendEntries to prevent election.
// - if we're in the process of slicing an AppendEntries with a large log entry payload. In this case we
// need to send an empty AppendEntries to prevent election.
boolean isInstallingSnaphot = followerLogInformation.getInstallSnapshotState() != null;
long leaderCommitIndex = isInstallingSnaphot || followerLogInformation.isLogEntrySlicingInProgress()
|| !followerLogInformation.isFollowerActive() ? -1 : context.getCommitIndex();
long followerNextIndex = followerLogInformation.getNextIndex();
AppendEntries appendEntries = new AppendEntries(currentTerm(), context.getId(),
getLogEntryIndex(followerNextIndex - 1),
getLogEntryTerm(followerNextIndex - 1), entries,
leaderCommitIndex, super.getReplicatedToAllIndex(), context.getPayloadVersion());
if (!entries.isEmpty() || log.isTraceEnabled()) {
log.debug("{}: Sending AppendEntries to follower {}: {}", logName(), followerLogInformation.getId(),
appendEntries);
}
followerActor.tell(appendEntries, actor());
}
/**
* Initiates a snapshot capture to install on a follower.
*
*
* Install Snapshot works as follows
* 1. Leader initiates the capture snapshot by calling createSnapshot on the RaftActor.
* 2. On receipt of the CaptureSnapshotReply message, the RaftActor persists the snapshot and makes a call to
* the Leader's handleMessage with a SendInstallSnapshot message.
* 3. The Leader obtains and stores the Snapshot from the SendInstallSnapshot message and sends it in chunks to
* the Follower via InstallSnapshot messages.
* 4. For each chunk, the Follower sends back an InstallSnapshotReply.
* 5. On receipt of the InstallSnapshotReply for the last chunk, the Leader marks the install complete for that
* follower.
* 6. If another follower requires a snapshot and a snapshot has been collected (via SendInstallSnapshot)
* then send the existing snapshot in chunks to the follower.
*
* @param followerId the id of the follower.
* @return true if capture was initiated, false otherwise.
*/
public boolean initiateCaptureSnapshot(final String followerId) {
FollowerLogInformation followerLogInfo = followerToLog.get(followerId);
if (snapshotHolder.isPresent()) {
// If a snapshot is present in the memory, most likely another install is in progress no need to capture
// snapshot. This could happen if another follower needs an install when one is going on.
final ActorSelection followerActor = context.getPeerActorSelection(followerId);
// Note: sendSnapshotChunk will set the LeaderInstallSnapshotState.
sendSnapshotChunk(followerActor, followerLogInfo);
return true;
}
boolean captureInitiated = context.getSnapshotManager().captureToInstall(context.getReplicatedLog().last(),
this.getReplicatedToAllIndex(), followerId);
if (captureInitiated) {
followerLogInfo.setLeaderInstallSnapshotState(new LeaderInstallSnapshotState(
context.getConfigParams().getSnapshotChunkSize(), logName()));
}
return captureInitiated;
}
private boolean canInstallSnapshot(final long nextIndex) {
// If the follower's nextIndex is -1 then we might as well send it a snapshot
// Otherwise send it a snapshot only if the nextIndex is not present in the log but is present
// in the snapshot
return nextIndex == -1 || !context.getReplicatedLog().isPresent(nextIndex)
&& context.getReplicatedLog().isInSnapshot(nextIndex);
}
private void sendInstallSnapshot() {
log.debug("{}: sendInstallSnapshot", logName());
for (Entry e : followerToLog.entrySet()) {
String followerId = e.getKey();
ActorSelection followerActor = context.getPeerActorSelection(followerId);
FollowerLogInformation followerLogInfo = e.getValue();
if (followerActor != null) {
long nextIndex = followerLogInfo.getNextIndex();
if (followerLogInfo.getInstallSnapshotState() != null
|| context.getPeerInfo(followerId).getVotingState() == VotingState.VOTING_NOT_INITIALIZED
|| canInstallSnapshot(nextIndex)) {
sendSnapshotChunk(followerActor, followerLogInfo);
}
}
}
}
/**
* Sends a snapshot chunk to a given follower
* InstallSnapshot should qualify as a heartbeat too.
*/
private void sendSnapshotChunk(final ActorSelection followerActor, final FollowerLogInformation followerLogInfo) {
if (snapshotHolder.isPresent()) {
LeaderInstallSnapshotState installSnapshotState = followerLogInfo.getInstallSnapshotState();
if (installSnapshotState == null) {
installSnapshotState = new LeaderInstallSnapshotState(context.getConfigParams().getSnapshotChunkSize(),
logName());
followerLogInfo.setLeaderInstallSnapshotState(installSnapshotState);
}
try {
// Ensure the snapshot bytes are set - this is a no-op.
installSnapshotState.setSnapshotBytes(snapshotHolder.get().getSnapshotBytes());
if (!installSnapshotState.canSendNextChunk()) {
return;
}
byte[] nextSnapshotChunk = installSnapshotState.getNextChunk();
log.debug("{}: next snapshot chunk size for follower {}: {}", logName(), followerLogInfo.getId(),
nextSnapshotChunk.length);
int nextChunkIndex = installSnapshotState.incrementChunkIndex();
Optional serverConfig = Optional.absent();
if (installSnapshotState.isLastChunk(nextChunkIndex)) {
serverConfig = Optional.fromNullable(context.getPeerServerInfo(true));
}
followerActor.tell(
new InstallSnapshot(currentTerm(), context.getId(),
snapshotHolder.get().getLastIncludedIndex(),
snapshotHolder.get().getLastIncludedTerm(),
nextSnapshotChunk,
nextChunkIndex,
installSnapshotState.getTotalChunks(),
Optional.of(installSnapshotState.getLastChunkHashCode()),
serverConfig
).toSerializable(followerLogInfo.getRaftVersion()),
actor()
);
} catch (IOException e) {
throw new RuntimeException(e);
}
log.debug("{}: InstallSnapshot sent to follower {}, Chunk: {}/{}", logName(), followerActor.path(),
installSnapshotState.getChunkIndex(), installSnapshotState.getTotalChunks());
}
}
private void sendHeartBeat() {
if (!followerToLog.isEmpty()) {
log.trace("{}: Sending heartbeat", logName());
sendAppendEntries(context.getConfigParams().getHeartBeatInterval().toMillis(), true);
appendEntriesMessageSlicer.checkExpiredSlicedMessageState();
}
}
private void stopHeartBeat() {
if (heartbeatSchedule != null && !heartbeatSchedule.isCancelled()) {
heartbeatSchedule.cancel();
}
}
private void scheduleHeartBeat(final FiniteDuration interval) {
if (followerToLog.isEmpty()) {
// Optimization - do not bother scheduling a heartbeat as there are
// no followers
return;
}
stopHeartBeat();
// Schedule a heartbeat. When the scheduler triggers a SendHeartbeat
// message is sent to itself.
// Scheduling the heartbeat only once here because heartbeats do not
// need to be sent if there are other messages being sent to the remote
// actor.
heartbeatSchedule = context.getActorSystem().scheduler().scheduleOnce(
interval, context.getActor(), SendHeartBeat.INSTANCE,
context.getActorSystem().dispatcher(), context.getActor());
}
@Override
public void close() {
stopHeartBeat();
appendEntriesMessageSlicer.close();
}
@Override
public final String getLeaderId() {
return context.getId();
}
@Override
public final short getLeaderPayloadVersion() {
return context.getPayloadVersion();
}
protected boolean isLeaderIsolated() {
int minPresent = getMinIsolatedLeaderPeerCount();
for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
final PeerInfo peerInfo = context.getPeerInfo(followerLogInformation.getId());
if (peerInfo != null && peerInfo.isVoting() && followerLogInformation.isFollowerActive()) {
--minPresent;
if (minPresent == 0) {
return false;
}
}
}
return minPresent != 0;
}
// called from example-actor for printing the follower-states
public String printFollowerStates() {
final StringBuilder sb = new StringBuilder();
sb.append('[');
for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
sb.append('{');
sb.append(followerLogInformation.getId());
sb.append(" state:");
sb.append(followerLogInformation.isFollowerActive());
sb.append("},");
}
sb.append(']');
return sb.toString();
}
@VisibleForTesting
public FollowerLogInformation getFollower(final String followerId) {
return followerToLog.get(followerId);
}
@VisibleForTesting
public int followerLogSize() {
return followerToLog.size();
}
static class SnapshotHolder {
private final long lastIncludedTerm;
private final long lastIncludedIndex;
private final ByteSource snapshotBytes;
SnapshotHolder(final Snapshot snapshot, final ByteSource snapshotBytes) {
this.lastIncludedTerm = snapshot.getLastAppliedTerm();
this.lastIncludedIndex = snapshot.getLastAppliedIndex();
this.snapshotBytes = snapshotBytes;
}
long getLastIncludedTerm() {
return lastIncludedTerm;
}
long getLastIncludedIndex() {
return lastIncludedIndex;
}
ByteSource getSnapshotBytes() {
return snapshotBytes;
}
}
}