Class IndexDeletionPolicy

Expert: policy for deletion of stale IndexCommits.

Implement this interface, and pass it to one of the IndexWriter or IndexReader constructors, to customize when older point-in-time commits (IndexCommit) are deleted from the index directory. The default deletion policy is 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 IndexWriter removes the old commits. Note that doing so will increase the storage requirements of the index. See LUCENE-710 for details.

Implementers of sub-classes should make sure that Clone() returns an independent instance able to work with any other IndexWriter or Directory instance.

Inheritance

System.Object

IndexDeletionPolicy

KeepOnlyLastCommitDeletionPolicy

NoDeletionPolicy

SnapshotDeletionPolicy

Namespace: Lucene.Net.Index

Assembly: Lucene.Net.dll

Syntax

public abstract class IndexDeletionPolicy : object

Constructors

IndexDeletionPolicy()

Sole constructor, typically called by sub-classes constructors.

Declaration

protected IndexDeletionPolicy()

Methods

Clone()

Declaration

public virtual object Clone()

Returns

Type	Description
System.Object

OnCommit<T>(IList<T>)

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 Commit()} or Dispose() is called, or possibly not at all if the Rollback()} method 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.

Declaration

public abstract void OnCommit<T>(IList<T> commits)
    where T : IndexCommit

Parameters

Type	Name	Description
IList<T>	commits	List of IndexCommits, sorted by age (the 0th one is the oldest commit).

Type Parameters

Name	Description
T

OnInit<T>(IList<T>)

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().

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.

Declaration

public abstract void OnInit<T>(IList<T> commits)
    where T : IndexCommit

Parameters

Type	Name	Description
IList<T>	commits	List of current point-in-time commits (IndexCommit), sorted by age (the 0th one is the oldest commit). Note that for a new index this method is invoked with an empty list.

Type Parameters

Name	Description
T