Class IndexWriter

An IndexWriter creates and maintains an index.

Inheritance

System.Object

IndexWriter

Implements

System.IDisposable

ITwoPhaseCommit

Inherited Members

System.Object.Equals(System.Object)

System.Object.Equals(System.Object, System.Object)

System.Object.GetHashCode()

System.Object.GetType()

System.Object.MemberwiseClone()

System.Object.ReferenceEquals(System.Object, System.Object)

System.Object.ToString()

Namespace: Lucene.Net.Index

Assembly: Lucene.Net.dll

Syntax

public class IndexWriter : IDisposable, ITwoPhaseCommit

Remarks

The OpenMode option on OpenMode determines whether a new index is created, or whether an existing index is opened. Note that you can open an index with CREATE even while readers are using the index. The old readers will continue to search the "point in time" snapshot they had opened, and won't see the newly created index until they re-open. If CREATE_OR_APPEND is used IndexWriter will create a new index if there is not already an index at the provided path and otherwise open the existing index.

In either case, documents are added with AddDocument(IEnumerable<IIndexableField>) and removed with DeleteDocuments(Term) or DeleteDocuments(Query). A document can be updated with UpdateDocument(Term, IEnumerable<IIndexableField>) (which just deletes and then adds the entire document). When finished adding, deleting and updating documents, Dispose() should be called.

These changes are buffered in memory and periodically flushed to the Directory (during the above method calls). A flush is triggered when there are enough added documents since the last flush. Flushing is triggered either by RAM usage of the documents (see RAMBufferSizeMB) or the number of added documents (see MaxBufferedDocs). The default is to flush when RAM usage hits DEFAULT_RAM_BUFFER_SIZE_MB MB. For best indexing speed you should flush by RAM usage with a large RAM buffer. Additionally, if IndexWriter reaches the configured number of buffered deletes (see MaxBufferedDeleteTerms) the deleted terms and queries are flushed and applied to existing segments. In contrast to the other flush options RAMBufferSizeMB and MaxBufferedDocs, deleted terms won't trigger a segment flush. Note that flushing just moves the internal buffered state in IndexWriter into the index, but these changes are not visible to IndexReader until either Commit() or Dispose() is called. A flush may also trigger one or more segment merges which by default run with a background thread so as not to block the addDocument calls (see below for changing the Lucene.Net.Index.IndexWriter.mergeScheduler).

Opening an IndexWriter creates a lock file for the directory in use. Trying to open another IndexWriter on the same directory will lead to a LockObtainFailedException. The LockObtainFailedException is also thrown if an IndexReader on the same directory is used to delete documents from the index.

Expert: IndexWriter allows an optional IndexDeletionPolicy implementation to be specified. You can use this to control when prior commits are deleted from the index. The default policy is KeepOnlyLastCommitDeletionPolicy which removes all prior commits as soon as a new commit is done (this matches behavior before 2.2). Creating your own policy can allow you to explicitly keep previous "point in time" commits alive in the index for some time, to allow readers to refresh to the new commit without having the old commit deleted out from under them. This is necessary on filesystems like NFS that do not support "delete on last close" semantics, which Lucene's "point in time" search normally relies on.

Expert: IndexWriter allows you to separately change the Lucene.Net.Index.IndexWriter.mergePolicy and the Lucene.Net.Index.IndexWriter.mergeScheduler. The Lucene.Net.Index.IndexWriter.mergePolicy is invoked whenever there are changes to the segments in the index. Its role is to select which merges to do, if any, and return a MergePolicy.MergeSpecification describing the merges. The default is LogByteSizeMergePolicy. Then, the MergeScheduler is invoked with the requested merges and it decides when and how to run the merges. The default is ConcurrentMergeScheduler.

NOTE: if you hit an System.OutOfMemoryException then IndexWriter will quietly record this fact and block all future segment commits. This is a defensive measure in case any internal state (buffered documents and deletions) were corrupted. Any subsequent calls to Commit() will throw an System.InvalidOperationException. The only course of action is to call Dispose(), which internally will call Rollback(), to undo any changes to the index since the last commit. You can also just call Rollback() directly.

NOTE: IndexWriter instances are completely thread safe, meaning multiple threads can call any of its methods, concurrently. If your application requires external synchronization, you should not synchronize on the IndexWriter instance as this may cause deadlock; use your own (non-Lucene) objects instead.

NOTE: Do not use System.Threading.Thread.Interrupt on a thread that's within IndexWriter, as .NET will throw System.Threading.ThreadInterruptedException on any wait, sleep, or join including any lock statement with contention on it. As a result, it is not practical to try to support System.Threading.Thread.Interrupt due to the chance System.Threading.ThreadInterruptedException could potentially be thrown in the middle of a Commit() or somewhere in the application that will cause a deadlock.

We recommend using another shutdown mechanism to safely cancel a parallel operation. See: https://github.com/apache/lucenenet/issues/526.

Constructors

IndexWriter(Directory, IndexWriterConfig)

Constructs a new IndexWriter per the settings given in conf. If you want to make "live" changes to this writer instance, use Config.

NOTE: after ths writer is created, the given configuration instance cannot be passed to another writer. If you intend to do so, you should Clone() it beforehand.

Declaration

public IndexWriter(Directory d, IndexWriterConfig conf)

Parameters

Type	Name	Description
Directory	d	the index directory. The index is either created or appended according OpenMode.
IndexWriterConfig	conf	the configuration settings according to which IndexWriter should be initialized.

Exceptions

Type	Condition
System.IO.IOException	if the directory cannot be read/written to, or if it does not exist and OpenMode is APPEND or if there is any other low-level IO error

Fields

MAX_TERM_LENGTH

Absolute hard maximum length for a term, in bytes once encoded as UTF8. If a term arrives from the analyzer longer than this length, an System.ArgumentException is thrown and a message is printed to Lucene.Net.Index.IndexWriter.infoStream, if set (see SetInfoStream(InfoStream)).

Declaration

public static readonly int MAX_TERM_LENGTH

Field Value

Type	Description
System.Int32

SOURCE

Key for the source of a segment in the Diagnostics.

Declaration

public static readonly string SOURCE

Field Value

Type	Description
System.String

SOURCE_ADDINDEXES_READERS

Source of a segment which results from a call to AddIndexes(IndexReader[]).

Declaration

public static readonly string SOURCE_ADDINDEXES_READERS

Field Value

Type	Description
System.String

SOURCE_FLUSH

Source of a segment which results from a flush.

Declaration

public static readonly string SOURCE_FLUSH

Field Value

Type	Description
System.String

SOURCE_MERGE

Source of a segment which results from a merge of other segments.

Declaration

public static readonly string SOURCE_MERGE

Field Value

Type	Description
System.String

WRITE_LOCK_NAME

Name of the write lock in the index.

Declaration

public static readonly string WRITE_LOCK_NAME

Field Value

Type	Description
System.String

Properties

Analyzer

Gets the analyzer used by this index.

Declaration

public virtual Analyzer Analyzer { get; }

Property Value

Type	Description
Analyzer

CommitData

Returns the commit user data map that was last committed, or the one that was set on SetCommitData(IDictionary<String, String>).

Declaration

public IDictionary<string, string> CommitData { get; }

Property Value

Type	Description
System.Collections.Generic.IDictionary<System.String, System.String>

Config

Returns a LiveIndexWriterConfig, which can be used to query the IndexWriter current settings, as well as modify "live" ones.

Declaration

public virtual LiveIndexWriterConfig Config { get; }

Property Value

Type	Description
LiveIndexWriterConfig

Directory

Gets the Directory used by this index.

Declaration

public virtual Directory Directory { get; }

Property Value

Type	Description
Directory

IsClosed

Declaration

public virtual bool IsClosed { get; }

Property Value

Type	Description
System.Boolean

KeepFullyDeletedSegments

Only for testing.

Note

This API is for internal purposes only and might change in incompatible ways in the next release.

Declaration

public virtual bool KeepFullyDeletedSegments { get; set; }

Property Value

Type	Description
System.Boolean

MaxDoc

Gets total number of docs in this index, including docs not yet flushed (still in the RAM buffer), not counting deletions.

Declaration

public virtual int MaxDoc { get; }

Property Value

Type	Description
System.Int32

See Also

NumDocs

MergingSegments

Expert: to be used by a MergePolicy to avoid selecting merges for segments already being merged. The returned collection is not cloned, and thus is only safe to access if you hold IndexWriter's lock (which you do when IndexWriter invokes the MergePolicy).

Do not alter the returned collection!

Declaration

public virtual ICollection<SegmentCommitInfo> MergingSegments { get; }

Property Value

Type	Description
System.Collections.Generic.ICollection<SegmentCommitInfo>

NumDocs

Gets total number of docs in this index, including docs not yet flushed (still in the RAM buffer), and including deletions. NOTE: buffered deletions are not counted. If you really need these to be counted you should call Commit() first.

Declaration

public virtual int NumDocs { get; }

Property Value

Type	Description
System.Int32

See Also

MaxDoc

Methods

AddDocument(IEnumerable<IIndexableField>)

Adds a document to this index.

Note that if an System.Exception is hit (for example disk full) then the index will be consistent, but this document may not have been added. Furthermore, it's possible the index will have one segment in non-compound format even when using compound files (when a merge has partially succeeded).

This method periodically flushes pending documents to the Directory (see IndexWriter), and also periodically triggers segment merges in the index according to the MergePolicy in use.

Merges temporarily consume space in the directory. The amount of space required is up to 1X the size of all segments being merged, when no readers/searchers are open against the index, and up to 2X the size of all segments being merged when readers/searchers are open against the index (see ForceMerge(Int32) for details). The sequence of primitive merge operations performed is governed by the merge policy.

Note that each term in the document can be no longer than MAX_TERM_LENGTH in bytes, otherwise an System.ArgumentException will be thrown.

Note that it's possible to create an invalid Unicode string in java if a UTF16 surrogate pair is malformed. In this case, the invalid characters are silently replaced with the Unicode replacement character U+FFFD.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void AddDocument(IEnumerable<IIndexableField> doc)

Parameters

Type	Name	Description
System.Collections.Generic.IEnumerable<IIndexableField>	doc

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

AddDocument(IEnumerable<IIndexableField>, Analyzer)

Adds a document to this index, using the provided analyzer instead of the value of Analyzer.

See AddDocument(IEnumerable<IIndexableField>) for details on index and IndexWriter state after an System.Exception, and flushing/merging temporary free space requirements.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void AddDocument(IEnumerable<IIndexableField> doc, Analyzer analyzer)

Parameters

Type	Name	Description
System.Collections.Generic.IEnumerable<IIndexableField>	doc
Analyzer	analyzer

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

AddDocuments(IEnumerable<IEnumerable<IIndexableField>>)

Atomically adds a block of documents with sequentially assigned document IDs, such that an external reader will see all or none of the documents.

WARNING: the index does not currently record which documents were added as a block. Today this is fine, because merging will preserve a block. The order of documents within a segment will be preserved, even when child documents within a block are deleted. Most search features (like result grouping and block joining) require you to mark documents; when these documents are deleted these search features will not work as expected. Obviously adding documents to an existing block will require you the reindex the entire block.

However it's possible that in the future Lucene may merge more aggressively re-order documents (for example, perhaps to obtain better index compression), in which case you may need to fully re-index your documents at that time.

See AddDocument(IEnumerable<IIndexableField>) for details on index and IndexWriter state after an System.Exception, and flushing/merging temporary free space requirements.

NOTE: tools that do offline splitting of an index (for example, IndexSplitter in Lucene.Net.Misc) or re-sorting of documents (for example, IndexSorter in contrib) are not aware of these atomically added documents and will likely break them up. Use such tools at your own risk!

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Note

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

Declaration

public virtual void AddDocuments(IEnumerable<IEnumerable<IIndexableField>> docs)

Parameters

Type	Name	Description
System.Collections.Generic.IEnumerable<System.Collections.Generic.IEnumerable<IIndexableField>>	docs

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

AddDocuments(IEnumerable<IEnumerable<IIndexableField>>, Analyzer)

Atomically adds a block of documents, analyzed using the provided analyzer, with sequentially assigned document IDs, such that an external reader will see all or none of the documents.

Note

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

Declaration

public virtual void AddDocuments(IEnumerable<IEnumerable<IIndexableField>> docs, Analyzer analyzer)

Parameters

Type	Name	Description
System.Collections.Generic.IEnumerable<System.Collections.Generic.IEnumerable<IIndexableField>>	docs
Analyzer	analyzer

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

AddIndexes(IndexReader[])

Merges the provided indexes into this index.

The provided IndexReaders are not closed.

See AddIndexes(IndexReader[]) for details on transactional semantics, temporary free space required in the Directory, and non-CFS segments on an System.Exception.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

NOTE: empty segments are dropped by this method and not added to this index.

NOTE: this method merges all given IndexReaders in one merge. If you intend to merge a large number of readers, it may be better to call this method multiple times, each time with a small set of readers. In principle, if you use a merge policy with a mergeFactor or maxMergeAtOnce parameter, you should pass that many readers in one call. Also, if the given readers are DirectoryReaders, they can be opened with termIndexInterval=-1 to save RAM, since during merge the in-memory structure is not used. See Open(Directory, Int32).

NOTE: if you call Dispose(Boolean) with false, which aborts all running merges, then any thread still running this method might hit a MergePolicy.MergeAbortedException.

Declaration

public virtual void AddIndexes(params IndexReader[] readers)

Parameters

Type	Name	Description
IndexReader[]	readers

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

AddIndexes(Directory[])

Adds all segments from an array of indexes into this index.

This may be used to parallelize batch indexing. A large document collection can be broken into sub-collections. Each sub-collection can be indexed in parallel, on a different thread, process or machine. The complete index can then be created by merging sub-collection indexes with this method.

NOTE: this method acquires the write lock in each directory, to ensure that no IndexWriter is currently open or tries to open while this is running.

This method is transactional in how System.Exceptions are handled: it does not commit a new segments_N file until all indexes are added. this means if an System.Exception occurs (for example disk full), then either no indexes will have been added or they all will have been.

Note that this requires temporary free space in the Directory up to 2X the sum of all input indexes (including the starting index). If readers/searchers are open against the starting index, then temporary free space required will be higher by the size of the starting index (see ForceMerge(Int32) for details).

NOTE: this method only copies the segments of the incoming indexes and does not merge them. Therefore deleted documents are not removed and the new segments are not merged with the existing ones.

This requires this index not be among those to be added.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void AddIndexes(params Directory[] dirs)

Parameters

Type	Name	Description
Directory[]	dirs

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error
LockObtainFailedException	if we were unable to acquire the write lock in at least one directory

Commit()

Commits all pending changes (added & deleted documents, segment merges, added indexes, etc.) to the index, and syncs all referenced index files, such that a reader will see the changes and the index updates will survive an OS or machine crash or power loss. Note that this does not wait for any running background merges to finish. This may be a costly operation, so you should test the cost in your application and do it only when really necessary.

Note that this operation calls Sync(ICollection<String>) on the index files. That call should not return until the file contents & metadata are on stable storage. For FSDirectory, this calls the OS's fsync. But, beware: some hardware devices may in fact cache writes even during fsync, and return before the bits are actually on stable storage, to give the appearance of faster performance. If you have such a device, and it does not have a battery backup (for example) then on power loss it may still lose data. Lucene cannot guarantee consistency on such devices.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public void Commit()

DeleteAll()

Delete all documents in the index.

This method will drop all buffered documents and will remove all segments from the index. This change will not be visible until a Commit() has been called. This method can be rolled back using Rollback().

NOTE: this method is much faster than using DeleteDocuments(new MatchAllDocsQuery()). Yet, this method also has different semantics compared to DeleteDocuments(Query) / DeleteDocuments(Query[]) since internal data-structures are cleared as well as all segment information is forcefully dropped anti-viral semantics like omitting norms are reset or doc value types are cleared. Essentially a call to DeleteAll() is equivalent to creating a new IndexWriter with CREATE which a delete query only marks documents as deleted.

NOTE: this method will forcefully abort all merges in progress. If other threads are running ForceMerge(Int32), AddIndexes(IndexReader[]) or ForceMergeDeletes() methods, they may receive MergePolicy.MergeAbortedExceptions.

Declaration

public virtual void DeleteAll()

DeleteDocuments(Term)

Deletes the document(s) containing term.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void DeleteDocuments(Term term)

Parameters

Type	Name	Description
Term	term	the term to identify the documents to be deleted

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

DeleteDocuments(Term[])

Deletes the document(s) containing any of the terms. All given deletes are applied and flushed atomically at the same time.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void DeleteDocuments(params Term[] terms)

Parameters

Type	Name	Description
Term[]	terms	array of terms to identify the documents to be deleted

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

DeleteDocuments(Query)

Deletes the document(s) matching the provided query.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void DeleteDocuments(Query query)

Parameters

Type	Name	Description
Query	query	the query to identify the documents to be deleted

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

DeleteDocuments(Query[])

Deletes the document(s) matching any of the provided queries. All given deletes are applied and flushed atomically at the same time.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void DeleteDocuments(params Query[] queries)

Parameters

Type	Name	Description
Query[]	queries	array of queries to identify the documents to be deleted

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

DeleteUnusedFiles()

Expert: remove any index files that are no longer used.

IndexWriter normally deletes unused files itself, during indexing. However, on Windows, which disallows deletion of open files, if there is a reader open on the index then those files cannot be deleted. This is fine, because IndexWriter will periodically retry the deletion.

However, IndexWriter doesn't try that often: only on open, close, flushing a new segment, and finishing a merge. If you don't do any of these actions with your IndexWriter, you'll see the unused files linger. If that's a problem, call this method to delete them (once you've closed the open readers that were preventing their deletion).

In addition, you can call this method to delete unreferenced index commits. this might be useful if you are using an IndexDeletionPolicy which holds onto index commits until some criteria are met, but those commits are no longer needed. Otherwise, those commits will be deleted the next time Commit() is called.

Declaration

public virtual void DeleteUnusedFiles()

Dispose()

Commits all changes to an index, waits for pending merges to complete, and closes all associated files.

This is a "slow graceful shutdown" which may take a long time especially if a big merge is pending: If you only want to close resources use Rollback(). If you only want to commit pending changes and close resources see Dispose(Boolean).

Note that this may be a costly operation, so, try to re-use a single writer instead of closing and opening a new one. See Commit() for caveats about write caching done by some IO devices.

If an System.Exception is hit during close, eg due to disk full or some other reason, then both the on-disk index and the internal state of the IndexWriter instance will be consistent. However, the close will not be complete even though part of it (flushing buffered documents) may have succeeded, so the write lock will still be held.

If you can correct the underlying cause (eg free up some disk space) then you can call Dispose() again. Failing that, if you want to force the write lock to be released (dangerous, because you may then lose buffered docs in the IndexWriter instance) then you can do something like this:

try 
{
    writer.Dispose();
} 
finally 
{
    if (IndexWriter.IsLocked(directory)) 
    {
        IndexWriter.Unlock(directory);
    }
}

after which, you must be certain not to use the writer instance anymore.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer, again. See IndexWriter for details.

Declaration

public void Dispose()

Exceptions

Type	Condition
System.IO.IOException	if there is a low-level IO error

Dispose(Boolean)

Closes the index with or without waiting for currently running merges to finish. This is only meaningful when using a MergeScheduler that runs merges in background threads.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer, again. See IndexWriter for details.

NOTE: it is dangerous to always call Dispose(false), especially when IndexWriter is not open for very long, because this can result in "merge starvation" whereby long merges will never have a chance to finish. This will cause too many segments in your index over time.

Declaration

public virtual void Dispose(bool waitForMerges)

Parameters

Type	Name	Description
System.Boolean	waitForMerges	if true, this call will block until all merges complete; else, it will ask all running merges to abort, wait until those merges have finished (which should be at most a few seconds), and then return.

DoAfterFlush()

A hook for extending classes to execute operations after pending added and deleted documents have been flushed to the Directory but before the change is committed (new segments_N file written).

Declaration

protected virtual void DoAfterFlush()

DoBeforeFlush()

A hook for extending classes to execute operations before pending added and deleted documents are flushed to the Directory.

Declaration

protected virtual void DoBeforeFlush()

EnsureOpen()

Used internally to throw an System.ObjectDisposedException if this IndexWriter has been disposed (closed=true) or is in the process of disposing (closing=true).

Calls EnsureOpen(Boolean).

Declaration

protected void EnsureOpen()

Exceptions

Type	Condition
System.ObjectDisposedException	if this IndexWriter is disposed

EnsureOpen(Boolean)

Used internally to throw an System.ObjectDisposedException if this IndexWriter has been disposed or is in the process of diposing.

Declaration

protected void EnsureOpen(bool failIfDisposing)

Parameters

Type	Name	Description
System.Boolean	failIfDisposing	if true, also fail when IndexWriter is in the process of disposing (closing=true) but not yet done disposing ( closed=false)

Exceptions

Type	Condition
System.ObjectDisposedException	if this IndexWriter is closed or in the process of closing

Flush(Boolean, Boolean)

Flush all in-memory buffered updates (adds and deletes) to the Directory.

Declaration

public void Flush(bool triggerMerge, bool applyAllDeletes)

Parameters

Type	Name	Description
System.Boolean	triggerMerge	if true, we may merge segments (if deletes or docs were flushed) if necessary
System.Boolean	applyAllDeletes	whether pending deletes should also

ForceMerge(Int32)

Forces merge policy to merge segments until there are <= maxNumSegments. The actual merges to be executed are determined by the MergePolicy.

This is a horribly costly operation, especially when you pass a small maxNumSegments; usually you should only call this if the index is static (will no longer be changed).

Note that this requires up to 2X the index size free space in your Directory (3X if you're using compound file format). For example, if your index size is 10 MB then you need up to 20 MB free for this to complete (30 MB if you're using compound file format). Also, it's best to call Commit() afterwards, to allow IndexWriter to free up disk space.

If some but not all readers re-open while merging is underway, this will cause > 2X temporary space to be consumed as those new readers will then hold open the temporary segments at that time. It is best not to re-open readers while merging is running.

The actual temporary usage could be much less than these figures (it depends on many factors).

In general, once this completes, the total size of the index will be less than the size of the starting index. It could be quite a bit smaller (if there were many pending deletes) or just slightly smaller.

If an System.Exception is hit, for example due to disk full, the index will not be corrupted and no documents will be lost. However, it may have been partially merged (some segments were merged but not all), and it's possible that one of the segments in the index will be in non-compound format even when using compound file format. This will occur when the System.Exception is hit during conversion of the segment into compound format.

This call will merge those segments present in the index when the call started. If other threads are still adding documents and flushing segments, those newly created segments will not be merged unless you call ForceMerge(Int32) again.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

NOTE: if you call Dispose(Boolean) with false, which aborts all running merges, then any thread still running this method might hit a MergePolicy.MergeAbortedException.

Declaration

public virtual void ForceMerge(int maxNumSegments)

Parameters

Type	Name	Description
System.Int32	maxNumSegments	maximum number of segments left in the index after merging finishes

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

See Also

FindMerges(MergeTrigger, SegmentInfos)

ForceMerge(Int32, Boolean)

Just like ForceMerge(Int32), except you can specify whether the call should block until all merging completes. This is only meaningful with a Lucene.Net.Index.IndexWriter.mergeScheduler that is able to run merges in background threads.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void ForceMerge(int maxNumSegments, bool doWait)

Parameters

Type	Name	Description
System.Int32	maxNumSegments
System.Boolean	doWait

ForceMergeDeletes()

Forces merging of all segments that have deleted documents. The actual merges to be executed are determined by the MergePolicy. For example, the default TieredMergePolicy will only pick a segment if the percentage of deleted docs is over 10%.

This is often a horribly costly operation; rarely is it warranted.

To see how many deletions you have pending in your index, call NumDeletedDocs.

NOTE: this method first flushes a new segment (if there are indexed documents), and applies all buffered deletes.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void ForceMergeDeletes()

ForceMergeDeletes(Boolean)

Just like ForceMergeDeletes(), except you can specify whether the call should block until the operation completes. This is only meaningful with a MergeScheduler that is able to run merges in background threads.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

NOTE: if you call Dispose(Boolean) with false, which aborts all running merges, then any thread still running this method might hit a MergePolicy.MergeAbortedException.

Declaration

public virtual void ForceMergeDeletes(bool doWait)

Parameters

Type	Name	Description
System.Boolean	doWait

GetReader(Boolean)

Expert: returns a readonly reader, covering all committed as well as un-committed changes to the index. this provides "near real-time" searching, in that changes made during an IndexWriter session can be quickly made available for searching without closing the writer nor calling Commit().

Note that this is functionally equivalent to calling Flush() and then opening a new reader. But the turnaround time of this method should be faster since it avoids the potentially costly Commit().

You must close the IndexReader returned by this method once you are done using it.

It's near real-time because there is no hard guarantee on how quickly you can get a new reader after making changes with IndexWriter. You'll have to experiment in your situation to determine if it's fast enough. As this is a new and experimental feature, please report back on your findings so we can learn, improve and iterate.

The resulting reader supports DoOpenIfChanged(), but that call will simply forward back to this method (though this may change in the future).

The very first time this method is called, this writer instance will make every effort to pool the readers that it opens for doing merges, applying deletes, etc. This means additional resources (RAM, file descriptors, CPU time) will be consumed.

For lower latency on reopening a reader, you should set MergedSegmentWarmer to pre-warm a newly merged segment before it's committed to the index. This is important for minimizing index-to-search delay after a large merge.

If an AddIndexes* call is running in another thread, then this reader will only search those segments from the foreign index that have been successfully copied over, so far.

NOTE: Once the writer is disposed, any outstanding readers may continue to be used. However, if you attempt to reopen any of those readers, you'll hit an System.ObjectDisposedException.

Note

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

Declaration

public virtual DirectoryReader GetReader(bool applyAllDeletes)

Parameters

Type	Name	Description
System.Boolean	applyAllDeletes

Returns

Type	Description
DirectoryReader	IndexReader that covers entire index plus all changes made so far by this IndexWriter instance

Exceptions

Type	Condition
System.IO.IOException	If there is a low-level I/O error

HasDeletions()

Returns true if this index has deletions (including buffered deletions). Note that this will return true if there are buffered Term/Query deletions, even if it turns out those buffered deletions don't match any documents. Also, if a merge kicked off as a result of flushing a

Declaration

public virtual bool HasDeletions()

Returns

Type	Description
System.Boolean

HasPendingMerges()

Expert: returns true if there are merges waiting to be scheduled.

Note

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

Declaration

public virtual bool HasPendingMerges()

Returns

Type	Description
System.Boolean

HasUncommittedChanges()

Returns true if there may be changes that have not been committed. There are cases where this may return true when there are no actual "real" changes to the index, for example if you've deleted by Term or Query but that Term or Query does not match any documents. Also, if a merge kicked off as a result of flushing a new segment during Commit(), or a concurrent merged finished, this method may return true right after you had just called Commit().

Declaration

public bool HasUncommittedChanges()

Returns

Type	Description
System.Boolean

IsLocked(Directory)

Returns true iff the index in the named directory is currently locked.

Declaration

public static bool IsLocked(Directory directory)

Parameters

Type	Name	Description
Directory	directory	the directory to check for a lock

Returns

Type	Description
System.Boolean

Exceptions

Type	Condition
System.IO.IOException	if there is a low-level IO error

MaybeMerge()

Expert: asks the Lucene.Net.Index.IndexWriter.mergePolicy whether any merges are necessary now and if so, runs the requested merges and then iterate (test again if merges are needed) until no more merges are returned by the Lucene.Net.Index.IndexWriter.mergePolicy.

Explicit calls to MaybeMerge() are usually not necessary. The most common case is when merge policy parameters have changed.

this method will call the Lucene.Net.Index.IndexWriter.mergePolicy with EXPLICIT.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public void MaybeMerge()

Merge(MergePolicy.OneMerge)

Merges the indicated segments, replacing them in the stack with a single segment.

Note

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

Declaration

public virtual void Merge(MergePolicy.OneMerge merge)

Parameters

Type	Name	Description
MergePolicy.OneMerge	merge

MergeFinish(MergePolicy.OneMerge)

Does fininishing for a merge, which is fast but holds the synchronized lock on IndexWriter instance.

Declaration

public void MergeFinish(MergePolicy.OneMerge merge)

Parameters

Type	Name	Description
MergePolicy.OneMerge	merge

NextMerge()

Expert: the Lucene.Net.Index.IndexWriter.mergeScheduler calls this method to retrieve the next merge requested by the MergePolicy

Note

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

Declaration

public virtual MergePolicy.OneMerge NextMerge()

Returns

Type	Description
MergePolicy.OneMerge

NumDeletedDocs(SegmentCommitInfo)

Obtain the number of deleted docs for a pooled reader. If the reader isn't being pooled, the segmentInfo's delCount is returned.

Declaration

public virtual int NumDeletedDocs(SegmentCommitInfo info)

Parameters

Type	Name	Description
SegmentCommitInfo	info

Returns

Type	Description
System.Int32

NumRamDocs()

Expert: Return the number of documents currently buffered in RAM.

Declaration

public int NumRamDocs()

Returns

Type	Description
System.Int32

PrepareCommit()

Expert: prepare for commit. This does the first phase of 2-phase commit. this method does all steps necessary to commit changes since this writer was opened: flushes pending added and deleted docs, syncs the index files, writes most of next segments_N file. After calling this you must call either Commit() to finish the commit, or Rollback() to revert the commit and undo all changes done since the writer was opened.

You can also just call Commit() directly without PrepareCommit() first in which case that method will internally call PrepareCommit().

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public void PrepareCommit()

RamSizeInBytes()

Expert: Return the total size of all index files currently cached in memory. Useful for size management with flushRamDocs()

Declaration

public long RamSizeInBytes()

Returns

Type	Description
System.Int64

Rollback()

Close the IndexWriter without committing any changes that have occurred since the last commit (or since it was opened, if commit hasn't been called). this removes any temporary files that had been created, after which the state of the index will be the same as it was when Commit() was last called or when this writer was first opened. This also clears a previous call to PrepareCommit().

Declaration

public virtual void Rollback()

Exceptions

Type	Condition
System.IO.IOException	if there is a low-level IO error

SegString()

Returns a string description of all segments, for debugging.

Note

This API is for internal purposes only and might change in incompatible ways in the next release.

Declaration

public virtual string SegString()

Returns

Type	Description
System.String

SegString(SegmentCommitInfo)

Returns a string description of the specified segment, for debugging.

Note

This API is for internal purposes only and might change in incompatible ways in the next release.

Declaration

public virtual string SegString(SegmentCommitInfo info)

Parameters

Type	Name	Description
SegmentCommitInfo	info

Returns

Type	Description
System.String

SegString(IEnumerable<SegmentCommitInfo>)

Returns a string description of the specified segments, for debugging.

Note

This API is for internal purposes only and might change in incompatible ways in the next release.

Declaration

public virtual string SegString(IEnumerable<SegmentCommitInfo> infos)

Parameters

Type	Name	Description
System.Collections.Generic.IEnumerable<SegmentCommitInfo>	infos

Returns

Type	Description
System.String

SetCommitData(IDictionary<String, String>)

Sets the commit user data map. That method is considered a transaction by IndexWriter and will be committed (Commit() even if no other changes were made to the writer instance. Note that you must call this method before PrepareCommit(), or otherwise it won't be included in the follow-on Commit().

NOTE: the dictionary is cloned internally, therefore altering the dictionary's contents after calling this method has no effect.

Declaration

public void SetCommitData(IDictionary<string, string> commitUserData)

Parameters

Type	Name	Description
System.Collections.Generic.IDictionary<System.String, System.String>	commitUserData

TryDeleteDocument(IndexReader, Int32)

Expert: attempts to delete by document ID, as long as the provided readerIn is a near-real-time reader (from Open(IndexWriter, Boolean). If the provided readerIn is an NRT reader obtained from this writer, and its segment has not been merged away, then the delete succeeds and this method returns true; else, it returns false the caller must then separately delete by Term or Query.

NOTE: this method can only delete documents visible to the currently open NRT reader. If you need to delete documents indexed after opening the NRT reader you must use the other DeleteDocument() methods (e.g., DeleteDocuments(Term)).

Declaration

public virtual bool TryDeleteDocument(IndexReader readerIn, int docID)

Parameters

Type	Name	Description
IndexReader	readerIn
System.Int32	docID

Returns

Type	Description
System.Boolean

Unlock(Directory)

Forcibly unlocks the index in the named directory.

Caution: this should only be used by failure recovery code, when it is known that no other process nor thread is in fact currently accessing this index.

Declaration

public static void Unlock(Directory directory)

Parameters

Type	Name	Description
Directory	directory

UpdateBinaryDocValue(Term, String, BytesRef)

Updates a document's BinaryDocValues for field to the given value. this method can be used to 'unset' a document's value by passing null as the new value. Also, you can only update fields that already exist in the index, not add new fields through this method.

NOTE: this method currently replaces the existing value of all affected documents with the new value.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void UpdateBinaryDocValue(Term term, string field, BytesRef value)

Parameters

Type	Name	Description
Term	term	the term to identify the document(s) to be updated
System.String	field	field name of the BinaryDocValues field
BytesRef	value	new value for the field

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

UpdateDocument(Term, IEnumerable<IIndexableField>)

Updates a document by first deleting the document(s) containing term and then adding the new document. The delete and then add are atomic as seen by a reader on the same index (flush may happen only after the add).

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void UpdateDocument(Term term, IEnumerable<IIndexableField> doc)

Parameters

Type	Name	Description
Term	term	the term to identify the document(s) to be deleted
System.Collections.Generic.IEnumerable<IIndexableField>	doc	the document to be added

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

UpdateDocument(Term, IEnumerable<IIndexableField>, Analyzer)

Updates a document by first deleting the document(s) containing term and then adding the new document. The delete and then add are atomic as seen by a reader on the same index (flush may happen only after the add).

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void UpdateDocument(Term term, IEnumerable<IIndexableField> doc, Analyzer analyzer)

Parameters

Type	Name	Description
Term	term	the term to identify the document(s) to be deleted
System.Collections.Generic.IEnumerable<IIndexableField>	doc	the document to be added
Analyzer	analyzer	the analyzer to use when analyzing the document

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

UpdateDocuments(Term, IEnumerable<IEnumerable<IIndexableField>>)

Atomically deletes documents matching the provided delTerm and adds a block of documents with sequentially assigned document IDs, such that an external reader will see all or none of the documents.

Note

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

Declaration

public virtual void UpdateDocuments(Term delTerm, IEnumerable<IEnumerable<IIndexableField>> docs)

Parameters

Type	Name	Description
Term	delTerm
System.Collections.Generic.IEnumerable<System.Collections.Generic.IEnumerable<IIndexableField>>	docs

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

See Also

AddDocuments(IEnumerable<IEnumerable<IIndexableField>>)

UpdateDocuments(Term, IEnumerable<IEnumerable<IIndexableField>>, Analyzer)

Atomically deletes documents matching the provided delTerm and adds a block of documents, analyzed using the provided analyzer, with sequentially assigned document IDs, such that an external reader will see all or none of the documents.

Note

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

Declaration

public virtual void UpdateDocuments(Term delTerm, IEnumerable<IEnumerable<IIndexableField>> docs, Analyzer analyzer)

Parameters

Type	Name	Description
Term	delTerm
System.Collections.Generic.IEnumerable<System.Collections.Generic.IEnumerable<IIndexableField>>	docs
Analyzer	analyzer

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

See Also

AddDocuments(IEnumerable<IEnumerable<IIndexableField>>)

UpdateNumericDocValue(Term, String, Nullable<Int64>)

Updates a document's NumericDocValues for field to the given value. This method can be used to 'unset' a document's value by passing null as the new value. Also, you can only update fields that already exist in the index, not add new fields through this method.

NOTE: if this method hits an System.OutOfMemoryException you should immediately dispose the writer. See IndexWriter for details.

Declaration

public virtual void UpdateNumericDocValue(Term term, string field, long? value)

Parameters

Type	Name	Description
Term	term	the term to identify the document(s) to be updated
System.String	field	field name of the NumericDocValues field
System.Nullable<System.Int64>	value	new value for the field

Exceptions

Type	Condition
CorruptIndexException	if the index is corrupt
System.IO.IOException	if there is a low-level IO error

WaitForMerges()

Wait for any currently outstanding merges to finish.

It is guaranteed that any merges started prior to calling this method will have completed once this method completes.

Declaration

public virtual void WaitForMerges()

Implements

System.IDisposable

ITwoPhaseCommit