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IndexDeletionPolicy.javaAPI DocApache Lucene 2.2.04244Sat Jun 16 22:20:36 BST 2007org.apache.lucene.index

IndexDeletionPolicy

public interface IndexDeletionPolicy

Expert: policy for deletion of stale {@link IndexCommitPoint index commits}.

Implement this interface, and pass it to one of the {@link IndexWriter} or {@link IndexReader} constructors, to customize when older {@link IndexCommitPoint point-in-time commits} are deleted from the index directory. The default deletion policy is {@link KeepOnlyLastCommitDeletionPolicy}, which always removes old commits as soon as a new commit is done (this matches the behavior before 2.2).

One expected use case for this (and the reason why it was first created) is to work around problems with an index directory accessed via filesystems like NFS because NFS does not provide the "delete on last close" semantics that Lucene's "point in time" search normally relies on. By implementing a custom deletion policy, such as "a commit is only removed once it has been stale for more than X minutes", you can give your readers time to refresh to the new commit before {@link IndexWriter} removes the old commits. Note that doing so will increase the storage requirements of the index. See LUCENE-710 for details.

Fields Summary
Constructors Summary
Methods Summary
public voidonCommit(java.util.List commits)

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 {@link IndexCommitPoint#delete delete()} of {@link IndexCommitPoint}.

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

param
commits List of {@link IndexCommitPoint}, sorted by age (the 0th one is the oldest commit).

public voidonInit(java.util.List commits)
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 {@link IndexCommitPoint#delete delete()}
of {@link 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.
param
commits List of current
{@link IndexCommitPoint point-in-time commits},
sorted by age (the 0th one is the oldest commit).