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https://issues.apache.org/jira/browse/RATIS-498?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16800680#comment-16800680
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Tsz Wo Nicholas Sze commented on RATIS-498:
-------------------------------------------
In notifyStateMachineToInstallSnapshot, we should
# Check if latest snapshot is already ahead of the requested index.
# Check if another request is in progress.
# Process the request.
#* Also, since we need to reset inProgressInstallSnapshotRequest, it is better
to use whenComplete as in your earlier patch.
{code}
private InstallSnapshotReplyProto notifyStateMachineToInstallSnapshot(
InstallSnapshotRequestProto request, RaftPeerId leaderId) throws
IOException {
...
updateLastRpcTime(FollowerState.UpdateType.INSTALL_SNAPSHOT_NOTIFICATION);
// Check if latest snapshot is already ahead of the requested index.
final TermIndex latestSnapshot = state.getLatestInstalledSnapshot();
if (latestSnapshot != null && latestSnapshot.getIndex() >=
firstAvailableLogIndex - 1) {
// State Machine has already installed the snapshot. Return the latest
snapshot index to the Leader.
final InstallSnapshotReplyProto reply =
ServerProtoUtils.toInstallSnapshotReplyProto(
leaderId, getId(), groupId, currentTerm,
InstallSnapshotResult.INSTALLED, latestSnapshot.getIndex());
LOG.info("{}: StateMachine latest installed snapshot index: {}. Reply:
{}",
getId(), latestSnapshot.getIndex(), reply);
return reply;
}
// Check if another request is in progress
if (!inProgressInstallSnapshotRequest.compareAndSet(null,
firstAvailableLogTermIndex)) {
return ServerProtoUtils.toInstallSnapshotReplyProto(leaderId, getId(),
groupId,
currentTerm, InstallSnapshotResult.ERROR, -1);
}
// This is the first installSnapshot notify request for this term and
// index. Notify the state machine to install the snapshot.
LOG.debug("{}: notifying state machine to install snapshot. Next log " +
"index is {} but the leader's first available log index is {}.",
getId(), state.getLog().getNextIndex(), firstAvailableLogIndex);
stateMachine.notifyInstallSnapshotFromLeader(firstAvailableLogTermIndex)
.whenComplete((reply, exception) -> {
if
(!inProgressInstallSnapshotRequest.compareAndSet(firstAvailableLogTermIndex,
null)) {
LOG.error("{}: TermIndex mismatched: firstAvailableLogTermIndex =
{} but inProgressInstallSnapshotRequest = {}",
getId(), firstAvailableLogTermIndex,
inProgressInstallSnapshotRequest);
return;
}
if (reply != null) {
synchronized (this) {
stateMachine.pause();
state.reloadStateMachine(reply.getIndex(), leaderTerm);
state.updateInstalledSnapshotIndex(reply);
}
} else {
// TODO: how to deal with the failure?
LOG.error(getId() + ": State Machine failed to install snapshot",
exception);
}
});
LOG.debug("{}: StateMachine snapshot installation is in progress. " +
"InProgress Request: {}", getId(),
inProgressInstallSnapshotRequest.get());
return ServerProtoUtils.toInstallSnapshotReplyProto(leaderId, getId(),
groupId,
currentTerm, InstallSnapshotResult.IN_PROGRESS, -1);
}
}
{code}
> Notify Follower to Install Snapshot through state machine
> ---------------------------------------------------------
>
> Key: RATIS-498
> URL: https://issues.apache.org/jira/browse/RATIS-498
> Project: Ratis
> Issue Type: New Feature
> Components: server
> Reporter: Hanisha Koneru
> Assignee: Hanisha Koneru
> Priority: Major
> Attachments: RATIS-498.000.patch, RATIS-498.001.patch,
> RATIS-498.002.patch, RATIS-498.003.patch, RATIS-498.004.patch
>
>
> When a lagging Follower wants to catch up with the Leader, and the Leader
> only has logs with start index greater than the Followers's last log index,
> then the leader sends an InstallSnapshotRequest to the the Follower.
> The aim of this Jira is to allow State Machine to decouple snapshot
> installation from the Ratis server. When Leader does not have the logs to get
> the Follower up to speed, it should notify the Follower to install a snapshot
> (if install snapshot through Log Appender is disabled). The Follower in turn
> notifies its state machine that a snapshot is required to catch up with the
> leader.
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