public abstract class IndexDeletionPolicy extends Object implements Cloneable
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.
Modifier | Constructor and Description |
---|---|
protected |
IndexDeletionPolicy()
Sole constructor, typically called by sub-classes constructors.
|
Modifier and Type | Method and Description |
---|---|
IndexDeletionPolicy |
clone() |
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.
|
protected IndexDeletionPolicy()
public abstract void onInit(List<? extends IndexCommit> commits) throws IOException
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.
commits
- List of current
point-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.IOException
public abstract void onCommit(List<? extends IndexCommit> commits) throws IOException
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()
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.
commits
- List of IndexCommit
,
sorted by age (the 0th one is the oldest commit).IOException
public IndexDeletionPolicy clone()
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