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.

Note

This API is experimental and might change in incompatible ways in the next release.

Inheritance

object

IndexDeletionPolicy

SnapshotDeletionPolicy

PersistentSnapshotDeletionPolicy

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Namespace: Lucene.Net.Index

Assembly: Lucene.Net.dll

Syntax

public class SnapshotDeletionPolicy : IndexDeletionPolicy

Constructors

SnapshotDeletionPolicy(IndexDeletionPolicy)

Sole constructor, taking the incoming IndexDeletionPolicy to wrap.

Declaration

public SnapshotDeletionPolicy(IndexDeletionPolicy primary)

Parameters

Type	Name	Description
IndexDeletionPolicy	primary

Fields

m_indexCommits

Used to map gen to IndexCommit.

Declaration

protected IDictionary<long, IndexCommit> m_indexCommits

Field Value

Type	Description
IDictionary<long, IndexCommit>

m_lastCommit

Most recently committed IndexCommit.

Declaration

protected IndexCommit m_lastCommit

Field Value

Type	Description
IndexCommit

m_refCounts

Records how many snapshots are held against each commit generation

Declaration

protected IDictionary<long, int> m_refCounts

Field Value

Type	Description
IDictionary<long, int>

Properties

SnapshotCount

Returns the total number of snapshots currently held.

Declaration

public virtual int SnapshotCount { get; }

Property Value

Type	Description
int

Methods

Clone()

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.

Note

This API is experimental and might change in incompatible ways in the next release.

Declaration

public override object Clone()

Returns

Type	Description
object

Overrides

IndexDeletionPolicy.Clone()

GetIndexCommit(long)

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
long	gen

Returns

Type	Description
IndexCommit

GetSnapshots()

Returns all IndexCommits held by at least one snapshot.

Declaration

public virtual IList<IndexCommit> GetSnapshots()

Returns

Type	Description
IList<IndexCommit>

IncRef(IndexCommit)

Increments the refCount for this IndexCommit.

Declaration

protected virtual void IncRef(IndexCommit ic)

Parameters

Type	Name	Description
IndexCommit	ic

OnCommit<T>(IList<T>)

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 Commit()} or Dispose() is called, or possibly not at all if the Rollback()} method 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.

Declaration

public override void OnCommit<T>(IList<T> commits) where T : IndexCommit

Parameters

Type	Name	Description
IList<T>	commits	List of IndexCommits, sorted by age (the 0th one is the oldest commit).

Type Parameters

Name	Description
T

Overrides

IndexDeletionPolicy.OnCommit<T>(IList<T>)

OnInit<T>(IList<T>)

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().

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.

Declaration

public override void OnInit<T>(IList<T> commits) where T : IndexCommit

Parameters

Type	Name	Description
IList<T>	commits	List of current point-in-time commits (IndexCommit), sorted by age (the 0th one is the oldest commit). Note that for a new index this method is invoked with an empty list.

Type Parameters

Name	Description
T

Overrides

IndexDeletionPolicy.OnInit<T>(IList<T>)

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()

ReleaseGen(long)

Release a snapshot by generation.

Declaration

protected virtual void ReleaseGen(long gen)

Parameters

Type	Name	Description
long	gen

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(int)) 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.

Exceptions

Type	Condition
InvalidOperationException	if this index does not have any commits yet