1 package org.apache.lucene.index;
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20 import java.util.List;
21 import java.io.IOException;
24 * <p>Expert: policy for deletion of stale {@link IndexCommit index commits}.
26 * <p>Implement this interface, and pass it to one
27 * of the {@link IndexWriter} or {@link IndexReader}
28 * constructors, to customize when older
29 * {@link IndexCommit point-in-time commits}
30 * are deleted from the index directory. The default deletion policy
31 * is {@link KeepOnlyLastCommitDeletionPolicy}, which always
32 * removes old commits as soon as a new commit is done (this
33 * matches the behavior before 2.2).</p>
35 * <p>One expected use case for this (and the reason why it
36 * was first created) is to work around problems with an
37 * index directory accessed via filesystems like NFS because
38 * NFS does not provide the "delete on last close" semantics
39 * that Lucene's "point in time" search normally relies on.
40 * By implementing a custom deletion policy, such as "a
41 * commit is only removed once it has been stale for more
42 * than X minutes", you can give your readers time to
43 * refresh to the new commit before {@link IndexWriter}
44 * removes the old commits. Note that doing so will
45 * increase the storage requirements of the index. See <a
47 * href="http://issues.apache.org/jira/browse/LUCENE-710">LUCENE-710</a>
51 public interface IndexDeletionPolicy {
54 * <p>This is called once when a writer is first
55 * instantiated to give the policy a chance to remove old
58 * <p>The writer locates all index commits present in the
59 * index directory and calls this method. The policy may
60 * choose to delete some of the commit points, doing so by
61 * calling method {@link IndexCommit#delete delete()}
62 * of {@link IndexCommit}.</p>
64 * <p><u>Note:</u> the last CommitPoint is the most recent one,
65 * i.e. the "front index state". Be careful not to delete it,
66 * unless you know for sure what you are doing, and unless
67 * you can afford to lose the index content while doing that.
69 * @param commits List of current
70 * {@link IndexCommit point-in-time commits},
71 * sorted by age (the 0th one is the oldest commit).
73 public void onInit(List<? extends IndexCommit> commits) throws IOException;
76 * <p>This is called each time the writer completed a commit.
77 * This gives the policy a chance to remove old commit points
78 * with each commit.</p>
80 * <p>The policy may now choose to delete old commit points
81 * by calling method {@link IndexCommit#delete delete()}
82 * of {@link IndexCommit}.</p>
84 * <p>This method is only called when {@link
85 * IndexWriter#commit} or {@link IndexWriter#close} is
86 * called, or possibly not at all if the {@link
87 * IndexWriter#rollback} is called.
89 * <p><u>Note:</u> the last CommitPoint is the most recent one,
90 * i.e. the "front index state". Be careful not to delete it,
91 * unless you know for sure what you are doing, and unless
92 * you can afford to lose the index content while doing that.
94 * @param commits List of {@link IndexCommit},
95 * sorted by age (the 0th one is the oldest commit).
97 public void onCommit(List<? extends IndexCommit> commits) throws IOException;