org.apache.lucene.index
Class SnapshotDeletionPolicy

java.lang.Object
  extended by 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. Note that you can re-use a single instance of SnapshotDeletionPolicy across multiple writers as long as they are against the same index Directory. Any snapshot held when a writer is closed will "survive" when the next writer is opened.

WARNING: This API is a new and experimental and may suddenly change.


Constructor Summary
SnapshotDeletionPolicy(IndexDeletionPolicy primary)
           
 
Method Summary
 void onCommit(List<? extends IndexCommit> commits)
          This is called each time the writer completed a commit.
 void onInit(List<? extends IndexCommit> 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.
 IndexCommit 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<? extends IndexCommit> 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 IndexCommit.

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<? extends IndexCommit> 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 IndexCommit.

This method is only called when IndexWriter.commit(long) or IndexWriter.close() is called, or possibly not at all if the IndexWriter.rollback() 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 IndexCommit, sorted by age (the 0th one is the oldest commit).
Throws:
IOException

snapshot

public IndexCommit 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.



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