Class SnapshotManager

java.lang.Object

com.loomcache.server.persistence.SnapshotManager

public class SnapshotManager
extends Object

Manages snapshots for WAL log compaction.

Provides:

• Snapshot creation with CRC32 integrity verification
• Snapshot loading with corruption detection
• Metadata-only loading (without full data)
• Automatic cleanup to maintain bounded snapshot storage

Snapshot format on disk: [lastIncludedIndex(8)][lastIncludedTerm(8)][timestamp(8)][dataLength(4)][data(variable)][checksum(4 CRC32)]

Snapshots are named: snapshot-{nodeId}-{index}.bin

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final record	SnapshotManager.Snapshot	Snapshot record containing index, term, timestamp, checksum, and data.
static final record	SnapshotManager.SnapshotInfo	Snapshot metadata without full data payload.

Constructor Summary

Constructors

Constructor	Description
SnapshotManager(String nodeId, Path snapshotDirectory)	Initialize the SnapshotManager.

Method Summary

Modifier and Type	Method	Description
void	cleanup(int maxSnapshots)	Clean up old snapshots, keeping only the latest N.
void	createSnapshot(long lastIncludedIndex, long lastIncludedTerm, byte[] data)	Create a snapshot of the current state.
void	deleteSnapshot(long index)	Delete a specific snapshot by index.
Optional<SnapshotManager.SnapshotInfo>	getSnapshotInfo()	Get metadata for the latest snapshot without loading the full data.
Optional<SnapshotManager.Snapshot>	loadLatestSnapshot()	Load the latest snapshot from disk.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

SnapshotManager

public SnapshotManager(String nodeId,
 Path snapshotDirectory)
                throws IOException

Initialize the SnapshotManager.

Parameters:

nodeId - The node identifier (must not be null or empty)

snapshotDirectory - The directory path for snapshot files (must not be null)

Throws:

IOException - If directory creation fails

IllegalArgumentException - If parameters are invalid

Method Details

createSnapshot

public void createSnapshot(long lastIncludedIndex,
 long lastIncludedTerm,
 byte[] data)
                    throws IOException

Create a snapshot of the current state.

The snapshot is written atomically to disk with CRC32 checksum for corruption detection on load.

Parameters:

lastIncludedIndex - The index of the last log entry included in this snapshot

lastIncludedTerm - The term of lastIncludedIndex

data - The snapshot data (state machine state)

Throws:

IOException - If write fails

IllegalArgumentException - If indices or term are invalid

loadLatestSnapshot

public Optional<SnapshotManager.Snapshot> loadLatestSnapshot()
                                                      throws IOException

Load the latest snapshot from disk.

Validates CRC32 checksum and returns the snapshot if valid. Returns empty if no valid snapshot exists.

Returns:

Optional containing the latest snapshot if found and valid

Throws:

IOException - If read fails

getSnapshotInfo

public Optional<SnapshotManager.SnapshotInfo> getSnapshotInfo()
                                                       throws IOException

Get metadata for the latest snapshot without loading the full data.

Returns:

Optional containing snapshot metadata if available

Throws:

IOException - If read fails

cleanup

public void cleanup(int maxSnapshots)
             throws IOException

Clean up old snapshots, keeping only the latest N.

Useful for managing disk space by removing snapshots that are no longer needed.

Parameters:

maxSnapshots - The maximum number of snapshots to keep

Throws:

IOException - If file operations fail

deleteSnapshot

public void deleteSnapshot(long index)
                    throws IOException

Delete a specific snapshot by index.

Parameters:

index - The snapshot index to delete

Throws:

IOException - If deletion fails