org.apache.lucene.index
Class SnapshotDeletionPolicy

java.lang.Object
  org.apache.lucene.index.SnapshotDeletionPolicy

All Implemented Interfaces:

IndexDeletionPolicy

public class SnapshotDeletionPolicy
extends Object
implements IndexDeletionPolicy

A IndexDeletionPolicy that wraps around any other IndexDeletionPolicy and adds the ability to hold and later release a single "snapshot" of an index. While the snapshot is held, the IndexWriter will not remove any files associated with it even if the index is otherwise being actively, arbitrarily changed. Because we wrap another arbitrary IndexDeletionPolicy, this gives you the freedom to continue using whatever IndexDeletionPolicy you would normally want to use with your index.

Constructor Summary

SnapshotDeletionPolicy(IndexDeletionPolicy primary)

Method Summary

void	onCommit(List commits) This is called each time the writer completed a commit.
void	onInit(List commits) This is called once when a writer is first instantiated to give the policy a chance to remove old commit points.
void	release() Release the currently held snapshot.
IndexCommitPoint	snapshot() Take a snapshot of the most recent commit to the index.

Methods inherited from class java.lang.Object

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

Constructor Detail

SnapshotDeletionPolicy

public SnapshotDeletionPolicy(IndexDeletionPolicy primary)

Method Detail

onInit

public void onInit(List commits)
            throws IOException

Description copied from interface: IndexDeletionPolicy

This is called once when a writer is first instantiated to give the policy a chance to remove old commit points.

The writer locates all index commits present in the index directory and calls this method. The policy may choose to delete some of the commit points, doing so by calling method delete() of IndexCommitPoint.

Note: the last CommitPoint is the most recent one, i.e. the "front index state". Be careful not to delete it, unless you know for sure what you are doing, and unless you can afford to lose the index content while doing that.

Specified by:

onInit in interface IndexDeletionPolicy

Parameters:

commits - List of current point-in-time commits, sorted by age (the 0th one is the oldest commit).

Throws:

IOException

onCommit

public void onCommit(List commits)
              throws IOException

Description copied from interface: IndexDeletionPolicy

This is called each time the writer completed a commit. This gives the policy a chance to remove old commit points with each commit.

The policy may now choose to delete old commit points by calling method delete() of IndexCommitPoint.

If writer has autoCommit = true then this method will in general be called many times during one instance of IndexWriter. If autoCommit = false then this method is only called once when IndexWriter.close() is called, or not at all if the IndexWriter.abort() is called.

Note: the last CommitPoint is the most recent one, i.e. the "front index state". Be careful not to delete it, unless you know for sure what you are doing, and unless you can afford to lose the index content while doing that.

Specified by:

onCommit in interface IndexDeletionPolicy

Parameters:

commits - List of IndexCommitPoint, sorted by age (the 0th one is the oldest commit).

Throws:

IOException

snapshot

public IndexCommitPoint snapshot()

Take a snapshot of the most recent commit to the index. You must call release() to free this snapshot. Note that while the snapshot is held, the files it references will not be deleted, which will consume additional disk space in your index. If you take a snapshot at a particularly bad time (say just before you call optimize()) then in the worst case this could consume an extra 1X of your total index size, until you release the snapshot.

release

public void release()

Release the currently held snapshot.