Class SnapshotDeletionPolicy

An 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.

This is a Lucene.NET EXPERIMENTAL API, use at your own risk
Inheritance
System.Object
IndexDeletionPolicy
SnapshotDeletionPolicy
PersistentSnapshotDeletionPolicy
Namespace: Lucene.Net.Index
Assembly: Lucene.Net.dll
Syntax
public class SnapshotDeletionPolicy : IndexDeletionPolicy

Constructors

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SnapshotDeletionPolicy(IndexDeletionPolicy)

Sole constructor, taking the incoming IndexDeletionPolicy to wrap.

Declaration
public SnapshotDeletionPolicy(IndexDeletionPolicy primary)
Parameters
Type Name Description
IndexDeletionPolicy primary

Fields

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m_indexCommits

Used to map gen to IndexCommit.

Declaration
protected IDictionary<long?, IndexCommit> m_indexCommits
Field Value
Type Description
IDictionary<System.Nullable<System.Int64>, IndexCommit>
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m_lastCommit

Most recently committed IndexCommit.

Declaration
protected IndexCommit m_lastCommit
Field Value
Type Description
IndexCommit
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m_refCounts

Records how many snapshots are held against each commit generation

Declaration
protected IDictionary<long, int> m_refCounts
Field Value
Type Description
IDictionary<System.Int64, System.Int32>

Properties

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SnapshotCount

Returns the total number of snapshots currently held.

Declaration
public virtual int SnapshotCount { get; }
Property Value
Type Description
System.Int32

Methods

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Clone()

Declaration
public override object Clone()
Returns
Type Description
System.Object
Overrides
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GetIndexCommit(Int64)

Retrieve an IndexCommit from its generation; returns null if this IndexCommit is not currently snapshotted

Declaration
public virtual IndexCommit GetIndexCommit(long gen)
Parameters
Type Name Description
System.Int64 gen
Returns
Type Description
IndexCommit
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GetSnapshots()

Returns all IndexCommits held by at least one snapshot.

Declaration
public virtual IList<IndexCommit> GetSnapshots()
Returns
Type Description
IList<IndexCommit>
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IncRef(IndexCommit)

Increments the refCount for this IndexCommit.

Declaration
protected virtual void IncRef(IndexCommit ic)
Parameters
Type Name Description
IndexCommit ic
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OnCommit<T>(IList<T>)

Declaration
public override void OnCommit<T>(IList<T> commits)
    where T : IndexCommit
Parameters
Type Name Description
IList<T> commits
Type Parameters
Name Description
T
Overrides
Lucene.Net.Index.IndexDeletionPolicy.OnCommit<T>(IList<T>)
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OnInit<T>(IList<T>)

Declaration
public override void OnInit<T>(IList<T> commits)
    where T : IndexCommit
Parameters
Type Name Description
IList<T> commits
Type Parameters
Name Description
T
Overrides
Lucene.Net.Index.IndexDeletionPolicy.OnInit<T>(IList<T>)
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Release(IndexCommit)

Release a snapshotted commit.

Declaration
public virtual void Release(IndexCommit commit)
Parameters
Type Name Description
IndexCommit commit

the commit previously returned by Snapshot()

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ReleaseGen(Int64)

Release a snapshot by generation.

Declaration
protected virtual void ReleaseGen(long gen)
Parameters
Type Name Description
System.Int64 gen
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Snapshot()

Snapshots the last commit and returns it. Once a commit is 'snapshotted,' it is protected from deletion (as long as this IndexDeletionPolicy is used). The snapshot can be removed by calling Release(IndexCommit) followed by a call to 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(Int32)) then in the worst case this could consume an extra 1X of your total index size, until you release the snapshot.

Declaration
public virtual IndexCommit Snapshot()
Returns
Type Description
IndexCommit

the IndexCommit that was snapshotted.