Class SnapshotDeletionPolicy
- Direct Known Subclasses:
PersistentSnapshotDeletionPolicy
IndexDeletionPolicy that wraps any other IndexDeletionPolicy and adds the
ability to hold and later release snapshots of an index. While a snapshot is held, the IndexWriter will not remove any files associated with it even if the index is otherwise being
actively, arbitrarily changed. Because we wrap another arbitrary IndexDeletionPolicy,
this gives you the freedom to continue using whatever IndexDeletionPolicy you would
normally want to use with your index.
This class maintains all snapshots in-memory, and so the information is not persisted and not
protected against system failures. If persistence is important, you can use PersistentSnapshotDeletionPolicy.
- WARNING: This API is experimental and might change in incompatible ways in the next release.
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected final Map<Long, IndexCommit> Used to map gen to IndexCommit.protected IndexCommitMost recently committedIndexCommit.Records how many snapshots are held against each commit generation -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptiongetIndexCommit(long gen) Retrieve anIndexCommitfrom its generation; returns null if this IndexCommit is not currently snapshottedintReturns the total number of snapshots currently held.Returns all IndexCommits held by at least one snapshot.protected voidincRef(IndexCommit ic) Increments the refCount for thisIndexCommit.voidonCommit(List<? extends IndexCommit> commits) This is called each time the writer completed a commit.voidonInit(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.voidrelease(IndexCommit commit) Release a snapshotted commit.protected voidreleaseGen(long gen) Release a snapshot by generation.snapshot()Snapshots the last commit and returns it.
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Field Details
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refCounts
Records how many snapshots are held against each commit generation -
indexCommits
Used to map gen to IndexCommit. -
lastCommit
Most recently committedIndexCommit.
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Constructor Details
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SnapshotDeletionPolicy
Sole constructor, taking the incomingIndexDeletionPolicyto wrap.
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Method Details
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onCommit
Description copied from class:IndexDeletionPolicyThis 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.
- Specified by:
onCommitin classIndexDeletionPolicy- Parameters:
commits- List ofIndexCommit, sorted by age (the 0th one is the oldest commit).- Throws:
IOException
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onInit
Description copied from class:IndexDeletionPolicyThis 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.
- Specified by:
onInitin classIndexDeletionPolicy- 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
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release
Release a snapshotted commit.- Parameters:
commit- the commit previously returned bysnapshot()- Throws:
IOException
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releaseGen
Release a snapshot by generation.- Throws:
IOException
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incRef
Increments the refCount for thisIndexCommit. -
snapshot
Snapshots the last commit and returns it. Once a commit is 'snapshotted,' it is protected from deletion (as long as thisIndexDeletionPolicyis used). The snapshot can be removed by callingrelease(IndexCommit)followed by a call toIndexWriter.deleteUnusedFiles().NOTE: while the snapshot is held, the files it references will not be deleted, which will consume additional disk space in your index. If you take a snapshot at a particularly bad time (say just before you call forceMerge) then in the worst case this could consume an extra 1X of your total index size, until you release the snapshot.
- Returns:
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IndexCommitthat was snapshotted. - Throws:
IllegalStateException- if this index does not have any commits yetIOException
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getSnapshots
Returns all IndexCommits held by at least one snapshot. -
getSnapshotCount
public int getSnapshotCount()Returns the total number of snapshots currently held. -
getIndexCommit
Retrieve anIndexCommitfrom its generation; returns null if this IndexCommit is not currently snapshotted
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