Module org.apache.lucene.core

Package org.apache.lucene.index

Class PersistentSnapshotDeletionPolicy

java.lang.Object

org.apache.lucene.index.IndexDeletionPolicy

org.apache.lucene.index.SnapshotDeletionPolicy

org.apache.lucene.index.PersistentSnapshotDeletionPolicy

public class PersistentSnapshotDeletionPolicy
extends SnapshotDeletionPolicy

A SnapshotDeletionPolicy which adds a persistence layer so that snapshots can be maintained across the life of an application. The snapshots are persisted in a Directory and are committed as soon as snapshot() or release(IndexCommit) is called.

NOTE: Sharing PersistentSnapshotDeletionPolicys that write to the same directory across IndexWriters will corrupt snapshots. You should make sure every IndexWriter has its own PersistentSnapshotDeletionPolicy and that they all write to a different Directory. It is OK to use the same Directory that holds the index.

This class adds a release(long) method to release commits from a previous snapshot's IndexCommit.getGeneration().

Field Summary

Fields

Modifier and Type	Field	Description
private static final String	CODEC_NAME
private final Directory	dir
private long	nextWriteGen
static final String	SNAPSHOTS_PREFIX	Prefix used for the save file.
private static final int	VERSION_CURRENT
private static final int	VERSION_START

Fields inherited from class org.apache.lucene.index.SnapshotDeletionPolicy

indexCommits, lastCommit, refCounts

Constructor Summary

Constructors

Constructor	Description
PersistentSnapshotDeletionPolicy(IndexDeletionPolicy primary, Directory dir)	PersistentSnapshotDeletionPolicy wraps another IndexDeletionPolicy to enable flexible snapshotting, passing IndexWriterConfig.OpenMode.CREATE_OR_APPEND by default.
PersistentSnapshotDeletionPolicy(IndexDeletionPolicy primary, Directory dir, IndexWriterConfig.OpenMode mode)	PersistentSnapshotDeletionPolicy wraps another IndexDeletionPolicy to enable flexible snapshotting.

Method Summary

Modifier and Type	Method	Description
private void	clearPriorSnapshots()
String	getLastSaveFile()	Returns the file name the snapshots are currently saved to, or null if no snapshots have been saved.
private void	loadPriorSnapshots()	Reads the snapshots information from the given Directory.
private void	persist()
void	release(long gen)	Deletes a snapshotted commit by generation.
void	release(IndexCommit commit)	Deletes a snapshotted commit.
IndexCommit	snapshot()	Snapshots the last commit.

Methods inherited from class org.apache.lucene.index.SnapshotDeletionPolicy

getIndexCommit, getSnapshotCount, getSnapshots, incRef, onCommit, onInit, releaseGen

Methods inherited from class java.lang.Object

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

Field Details

SNAPSHOTS_PREFIX

public static final String SNAPSHOTS_PREFIX

Prefix used for the save file.

See Also:

• Constant Field Values

VERSION_START

private static final int VERSION_START

See Also:

• Constant Field Values

VERSION_CURRENT

private static final int VERSION_CURRENT

See Also:

• Constant Field Values

CODEC_NAME

private static final String CODEC_NAME

See Also:

• Constant Field Values

nextWriteGen

private long nextWriteGen

dir

private final Directory dir

Constructor Details

PersistentSnapshotDeletionPolicy

public PersistentSnapshotDeletionPolicy(IndexDeletionPolicy primary,
 Directory dir)
                                 throws IOException

PersistentSnapshotDeletionPolicy wraps another IndexDeletionPolicy to enable flexible snapshotting, passing IndexWriterConfig.OpenMode.CREATE_OR_APPEND by default.

Parameters:

primary - the IndexDeletionPolicy that is used on non-snapshotted commits. Snapshotted commits, by definition, are not deleted until explicitly released via release(org.apache.lucene.index.IndexCommit).

dir - the Directory which will be used to persist the snapshots information.

Throws:

IOException

PersistentSnapshotDeletionPolicy

public PersistentSnapshotDeletionPolicy(IndexDeletionPolicy primary,
 Directory dir,
 IndexWriterConfig.OpenMode mode)
                                 throws IOException

PersistentSnapshotDeletionPolicy wraps another IndexDeletionPolicy to enable flexible snapshotting.

Parameters:

primary - the IndexDeletionPolicy that is used on non-snapshotted commits. Snapshotted commits, by definition, are not deleted until explicitly released via release(org.apache.lucene.index.IndexCommit).

dir - the Directory which will be used to persist the snapshots information.

mode - specifies whether a new index should be created, deleting all existing snapshots information (immediately), or open an existing index, initializing the class with the snapshots information.

Throws:

IOException

Method Details

snapshot

public IndexCommit snapshot()
                     throws IOException

Snapshots the last commit. Once this method returns, the snapshot information is persisted in the directory.

Overrides:

snapshot in class SnapshotDeletionPolicy

Returns:

the IndexCommit that was snapshotted.

Throws:

IOException

See Also:

• SnapshotDeletionPolicy.snapshot()

release

public void release(IndexCommit commit)
             throws IOException

Deletes a snapshotted commit. Once this method returns, the snapshot information is persisted in the directory.

Overrides:

release in class SnapshotDeletionPolicy

Parameters:

commit - the commit previously returned by SnapshotDeletionPolicy.snapshot()

Throws:

IOException

See Also:

• SnapshotDeletionPolicy.release(org.apache.lucene.index.IndexCommit)

release

public void release(long gen)
             throws IOException

Deletes a snapshotted commit by generation. Once this method returns, the snapshot information is persisted in the directory.

Throws:

IOException

See Also:

• IndexCommit.getGeneration()
• SnapshotDeletionPolicy.release(org.apache.lucene.index.IndexCommit)

persist

private void persist()
              throws IOException

Throws:

IOException

clearPriorSnapshots

private void clearPriorSnapshots()
                          throws IOException

Throws:

IOException

getLastSaveFile

public String getLastSaveFile()

Returns the file name the snapshots are currently saved to, or null if no snapshots have been saved.

loadPriorSnapshots

private void loadPriorSnapshots()
                         throws IOException

Reads the snapshots information from the given Directory. This method can be used if the snapshots information is needed, however you cannot instantiate the deletion policy (because e.g., some other process keeps a lock on the snapshots directory).

Throws:

IOException