Class IndexDeletionPolicy
- All Implemented Interfaces:
Cloneable
- Direct Known Subclasses:
KeepOnlyLastCommitDeletionPolicy
,NoDeletionPolicy
,SnapshotDeletionPolicy
Expert: policy for deletion of stale index commits
.
Implement this interface, and pass it to one
of the IndexWriter
or IndexReader
constructors, to customize when older
point-in-time commits
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.
-
Constructor Summary
ConstructorsModifierConstructorDescriptionprotected
Sole constructor, typically called by sub-classes constructors. -
Method Summary
Modifier and TypeMethodDescriptionclone()
abstract void
onCommit
(List<? extends IndexCommit> commits) This is called each time the writer completed a commit.abstract 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.
-
Constructor Details
-
IndexDeletionPolicy
protected IndexDeletionPolicy()Sole constructor, typically called by sub-classes constructors.
-
-
Method Details
-
onInit
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()
ofIndexCommit
.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.
- Parameters:
commits
- List of currentpoint-in-time commits
, sorted by age (the 0th one is the oldest commit). Note that for a new index this method is invoked with an empty list.- Throws:
IOException
-
onCommit
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()
ofIndexCommit
.This method is only called when
IndexWriter.commit()
orIndexWriter.close()
is called, or possibly not at all if theIndexWriter.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.
- Parameters:
commits
- List ofIndexCommit
, sorted by age (the 0th one is the oldest commit).- Throws:
IOException
-
clone
-