net.kuujo.catalog.server

Interface Commit<T extends Operation>

All Superinterfaces:

AutoCloseable

public interface Commit<T extends Operation>
extends AutoCloseable

Represents the committed state and metadata of a Raft state machine operation.

This class is used by the RaftServer internally to expose committed commands and queries to the user provided StateMachine. Operations that are wrapped in a Commit object are guaranteed to be persisted in the Raft log on a majority of the cluster. The commit object provides metadata about the committed operation such as the index() at which the operation was written in the log, the time() at which it was written, and the Session that submitted the operation.

Author:

Jordan Halterman

Method Summary

Modifier and Type	Method and Description
void	clean() Cleans the commit.
void	close() Closes the commit.
long	index() Returns the commit index.
T	operation() Returns the operation submitted by the user.
Session	session() Returns the session that submitted the operation.
Instant	time() Returns the time at which the operation was committed.
Class<T>	type() Returns the commit type.

Method Detail

index

long index()

Returns the commit index.

This is the index at which the committed Operation was written in the Raft log. Catalog guarantees that this index will be the same for all instances of the given operation on all nodes in the cluster.

Note that for Query operations, the returned index may actually represent the last committed index in the Raft log since queries are not actually written to disk. This, however, does not break the single index guarantee since queries will only be applied to the leader's StateMachine.

Returns:

The commit index.

session

Session session()

Returns the session that submitted the operation.

The returned Session is representative of the session that submitted the operation that resulted in this Commit. Note that the session will be provided regardless of whether the session is currently active in the cluster. However, attempts to Session.publish(Object) to inactive sessions will fail silently.

Additionally, because clients only connect to one server at any given time, the Session provided in any given commit to any StateMachine may or may not be capable of communicating with the client.

Returns:

The session that created the commit.

time

Instant time()

Returns the time at which the operation was committed.

The time is representative of the time at which the leader wrote the operation to its log. Because instants are replicated through the Raft consensus algorithm, they are guaranteed to be consistent across all servers and therefore can be used to perform time-dependent operations such as expiring keys or timeouts.

Users should never use System time to control behavior in a state machine and should instead rely upon Commit times for time-based controls.

Returns:

The commit time.

type

Class<T> type()

Returns the commit type.

This is the Class returned by the committed operation's Object.getClass() method.

Returns:

The commit type.

operation

T operation()

Returns the operation submitted by the user.

Returns:

The operation submitted by the user.

clean

void clean()

Cleans the commit.

When the commit is cleaned, it will be removed from the log and may be removed permanently from disk at some arbitrary point in the future.

close

void close()

Closes the commit.

Once the commit is closed, it may be recycled and should no longer be accessed by the closer.

Specified by:

close in interface AutoCloseable