io.atomix.protocols.raft.storage.snapshot

Class SnapshotStore

java.lang.Object

io.atomix.protocols.raft.storage.snapshot.SnapshotStore

All Implemented Interfaces:

AutoCloseable

public class SnapshotStore
extends Object
implements AutoCloseable

Persists server snapshots via the RaftStorage module.

The server snapshot store is responsible for persisting periodic state machine snapshots according to the configured storage level. Each server with a snapshottable state machine persists the state machine state to allow commands to be removed from disk.

When a snapshot store is created, the store will load any existing snapshots from disk and make them available for reading. Only snapshots that have been written and completed will be read from disk. Incomplete snapshots are automatically deleted from disk when the snapshot store is opened.

   
   SnapshotStore snapshots = storage.openSnapshotStore("test");
   Snapshot snapshot = snapshots.snapshot(1);
   
 

To create a new Snapshot, use the newSnapshot(ServiceId, String, long, WallClockTimestamp) method. Each snapshot must be created with a unique index which represents the index of the server state machine at the point at which the snapshot was taken. Snapshot indices are used to sort snapshots loaded from disk and apply them at the correct point in the state machine.

   
   Snapshot snapshot = snapshots.create(10);
   try (SnapshotWriter writer = snapshot.writer()) {
     ...
   }
   snapshot.complete();
   
 

Snapshots don't necessarily represent the beginning of the log. Typical Raft implementations take a snapshot of the state machine state and then clear their logs up to that point. However, in Raft a snapshot may actually only represent a subset of the state machine's state.

Constructor Summary

Constructors

Constructor and Description
SnapshotStore(RaftStorage storage)

Method Summary

Modifier and Type	Method and Description
void	close()
Snapshot	getSnapshotById(ServiceId id) Returns the last snapshot for the given state machine identifier.
Collection<Snapshot>	getSnapshotsByIndex(long index) Returns the snapshot at the given index.
Snapshot	newSnapshot(ServiceId serviceId, String serviceName, long index, io.atomix.time.WallClockTimestamp timestamp) Creates a new snapshot.
Snapshot	newTemporarySnapshot(ServiceId serviceId, String serviceName, long index, io.atomix.time.WallClockTimestamp timestamp) Creates a temporary in-memory snapshot.
String	toString()

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

SnapshotStore

public SnapshotStore(RaftStorage storage)

Method Detail

getSnapshotById

public Snapshot getSnapshotById(ServiceId id)

Returns the last snapshot for the given state machine identifier.

Parameters:

id - The state machine identifier for which to return the snapshot.

Returns:

The latest snapshot for the given state machine.

getSnapshotsByIndex

public Collection<Snapshot> getSnapshotsByIndex(long index)

Returns the snapshot at the given index.

Parameters:

index - The index for which to return the snapshot.

Returns:

The snapshot at the given index.

newTemporarySnapshot

public Snapshot newTemporarySnapshot(ServiceId serviceId,
                                     String serviceName,
                                     long index,
                                     io.atomix.time.WallClockTimestamp timestamp)

Creates a temporary in-memory snapshot.

Parameters:

serviceId - The snapshot identifier.

serviceName - The snapshot service name.

index - The snapshot index.

timestamp - The snapshot timestamp.

Returns:

The snapshot.

newSnapshot

public Snapshot newSnapshot(ServiceId serviceId,
                            String serviceName,
                            long index,
                            io.atomix.time.WallClockTimestamp timestamp)

Creates a new snapshot.

Parameters:

serviceId - The snapshot identifier.

serviceName - The snapshot service name.

index - The snapshot index.

timestamp - The snapshot timestamp.

Returns:

The snapshot.

close

public void close()

Specified by:

close in interface AutoCloseable

toString

public String toString()

Overrides:

toString in class Object