org.apache.lucene.index

Class DirectoryReader

java.lang.Object

org.apache.lucene.index.IndexReader

org.apache.lucene.index.CompositeReader

org.apache.lucene.index.BaseCompositeReader<LeafReader>

org.apache.lucene.index.DirectoryReader

All Implemented Interfaces:

Closeable, AutoCloseable

Direct Known Subclasses:

FilterDirectoryReader, StandardDirectoryReader

public abstract class DirectoryReader
extends BaseCompositeReader<LeafReader>

DirectoryReader is an implementation of CompositeReader that can read indexes in a Directory.

DirectoryReader instances are usually constructed with a call to one of the static open() methods, e.g. open(Directory).

For efficiency, in this API documents are often referred to via document numbers, non-negative integers which each name a unique document in the index. These document numbers are ephemeral -- they may change as documents are added to and deleted from an index. Clients should thus not rely on a given document having the same number between sessions.

NOTE: IndexReader 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 IndexReader instance; use your own (non-Lucene) objects instead.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.index.IndexReader

IndexReader.CacheHelper, IndexReader.CacheKey, IndexReader.ClosedListener

Field Summary

Fields

Modifier and Type	Field and Description
protected Directory	directory The index directory.

Fields inherited from class org.apache.lucene.index.BaseCompositeReader

subReadersSorter

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	DirectoryReader(Directory directory, LeafReader[] segmentReaders, Comparator<LeafReader> leafSorter) Expert: Constructs a DirectoryReader on the given subReaders.

Method Summary

Modifier and Type	Method and Description
Directory	directory() Returns the directory this index resides in.
protected abstract DirectoryReader	doOpenIfChanged() Implement this method to support openIfChanged(DirectoryReader).
protected abstract DirectoryReader	doOpenIfChanged(IndexCommit commit) Implement this method to support openIfChanged(DirectoryReader,IndexCommit).
protected abstract DirectoryReader	doOpenIfChanged(IndexWriter writer, boolean applyAllDeletes) Implement this method to support openIfChanged(DirectoryReader,IndexWriter,boolean).
abstract IndexCommit	getIndexCommit() Expert: return the IndexCommit that this reader has opened.
abstract long	getVersion() Version number when this IndexReader was opened.
static boolean	indexExists(Directory directory) Returns true if an index likely exists at the specified directory.
abstract boolean	isCurrent() Check whether any new changes have occurred to the index since this reader was opened.
static List<IndexCommit>	listCommits(Directory dir) Returns all commit points that exist in the Directory.
static DirectoryReader	open(Directory directory) Returns a IndexReader reading the index in the given Directory
static DirectoryReader	open(Directory directory, Comparator<LeafReader> leafSorter) Returns a IndexReader for the the index in the given Directory
static DirectoryReader	open(IndexCommit commit) Expert: returns an IndexReader reading the index in the given IndexCommit.
static DirectoryReader	open(IndexWriter writer) Open a near real time IndexReader from the IndexWriter.
static DirectoryReader	open(IndexWriter writer, boolean applyAllDeletes, boolean writeAllDeletes) Expert: open a near real time IndexReader from the IndexWriter, controlling whether past deletions should be applied.
static DirectoryReader	openIfChanged(DirectoryReader oldReader) If the index has changed since the provided reader was opened, open and return a new reader; else, return null.
static DirectoryReader	openIfChanged(DirectoryReader oldReader, IndexCommit commit) If the IndexCommit differs from what the provided reader is searching, open and return a new reader; else, return null.
static DirectoryReader	openIfChanged(DirectoryReader oldReader, IndexWriter writer) Expert: If there changes (committed or not) in the IndexWriter versus what the provided reader is searching, then open and return a new IndexReader searching both committed and uncommitted changes from the writer; else, return null (though, the current implementation never returns null).
static DirectoryReader	openIfChanged(DirectoryReader oldReader, IndexWriter writer, boolean applyAllDeletes) Expert: Opens a new reader, if there are any changes, controlling whether past deletions should be applied.

Methods inherited from class org.apache.lucene.index.BaseCompositeReader

docFreq, document, getDocCount, getSequentialSubReaders, getSumDocFreq, getSumTotalTermFreq, getTermVectors, maxDoc, numDocs, readerBase, readerIndex, totalTermFreq

Methods inherited from class org.apache.lucene.index.CompositeReader

getContext, toString

Methods inherited from class org.apache.lucene.index.IndexReader

close, decRef, doClose, document, document, ensureOpen, equals, getReaderCacheHelper, getRefCount, getTermVector, hasDeletions, hashCode, incRef, leaves, numDeletedDocs, registerParentReader, tryIncRef

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

directory

protected final Directory directory

The index directory.

Constructor Detail

DirectoryReader

protected DirectoryReader(Directory directory,
                          LeafReader[] segmentReaders,
                          Comparator<LeafReader> leafSorter)
                   throws IOException

Expert: Constructs a DirectoryReader on the given subReaders.

Parameters:

segmentReaders - the wrapped atomic index segment readers. This array is returned by BaseCompositeReader.getSequentialSubReaders() and used to resolve the correct subreader for docID-based methods. Please note: This array is not cloned and not protected for modification outside of this reader. Subclasses of DirectoryReader should take care to not allow modification of this internal array, e.g. doOpenIfChanged().

leafSorter - – a comparator for sorting leaf readers. If not null, this comparator is used for sorting leaf readers.

Throws:

IOException

Method Detail

open

public static DirectoryReader open(Directory directory)
                            throws IOException

Returns a IndexReader reading the index in the given Directory

Parameters:

directory - the index directory

Throws:

IOException - if there is a low-level IO error

open

public static DirectoryReader open(Directory directory,
                                   Comparator<LeafReader> leafSorter)
                            throws IOException

Returns a IndexReader for the the index in the given Directory

Parameters:

directory - the index directory

leafSorter - a comparator for sorting leaf readers. Providing leafSorter is useful for indices on which it is expected to run many queries with particular sort criteria (e.g. for time-based indices this is usually a descending sort on timestamp). In this case leafSorter should sort leaves according to this sort criteria. Providing leafSorter allows to speed up this particular type of sort queries by early terminating while iterating through segments and segments' documents.

Throws:

IOException - if there is a low-level IO error

open

public static DirectoryReader open(IndexWriter writer)
                            throws IOException

Open a near real time IndexReader from the IndexWriter.

Parameters:

writer - The IndexWriter to open from

Returns:

The new IndexReader

Throws:

CorruptIndexException - if the index is corrupt

IOException - if there is a low-level IO error

See Also:

openIfChanged(DirectoryReader,IndexWriter,boolean)

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

open

public static DirectoryReader open(IndexWriter writer,
                                   boolean applyAllDeletes,
                                   boolean writeAllDeletes)
                            throws IOException

Expert: open a near real time IndexReader from the IndexWriter, controlling whether past deletions should be applied.

Parameters:

writer - The IndexWriter to open from

applyAllDeletes - If true, all buffered deletes will be applied (made visible) in the returned reader. If false, the deletes are not applied but remain buffered (in IndexWriter) so that they will be applied in the future. Applying deletes can be costly, so if your app can tolerate deleted documents being returned you might gain some performance by passing false.

writeAllDeletes - If true, new deletes will be written down to index files instead of carried over from writer to reader directly in heap

Throws:

IOException

See Also:

open(IndexWriter)

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

open

public static DirectoryReader open(IndexCommit commit)
                            throws IOException

Expert: returns an IndexReader reading the index in the given IndexCommit.

Parameters:

commit - the commit point to open

Throws:

IOException - if there is a low-level IO error

openIfChanged

public static DirectoryReader openIfChanged(DirectoryReader oldReader)
                                     throws IOException

If the index has changed since the provided reader was opened, open and return a new reader; else, return null. The new reader, if not null, will be the same type of reader as the previous one, ie an NRT reader will open a new NRT reader, a MultiReader will open a new MultiReader, etc.

This method is typically far less costly than opening a fully new DirectoryReader as it shares resources (for example sub-readers) with the provided DirectoryReader, when possible.

The provided reader is not closed (you are responsible for doing so); if a new reader is returned you also must eventually close it. Be sure to never close a reader while other threads are still using it; see SearcherManager to simplify managing this.

Returns:

null if there are no changes; else, a new DirectoryReader instance which you must eventually close

Throws:

CorruptIndexException - if the index is corrupt

IOException - if there is a low-level IO error

openIfChanged

public static DirectoryReader openIfChanged(DirectoryReader oldReader,
                                            IndexCommit commit)
                                     throws IOException

If the IndexCommit differs from what the provided reader is searching, open and return a new reader; else, return null.

Throws:

IOException

See Also:

openIfChanged(DirectoryReader)

openIfChanged

public static DirectoryReader openIfChanged(DirectoryReader oldReader,
                                            IndexWriter writer)
                                     throws IOException

Expert: If there changes (committed or not) in the IndexWriter versus what the provided reader is searching, then open and return a new IndexReader searching both committed and uncommitted changes from the writer; else, return null (though, the current implementation never returns null).

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 IndexWriter.commit().

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 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 call IndexWriterConfig.setMergedSegmentWarmer(org.apache.lucene.index.IndexWriter.IndexReaderWarmer) 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 closed, any outstanding readers may continue to be used. However, if you attempt to reopen any of those readers, you'll hit an AlreadyClosedException.

Parameters:

writer - The IndexWriter to open from

Returns:

DirectoryReader that covers entire index plus all changes made so far by this IndexWriter instance, or null if there are no new changes

Throws:

IOException - if there is a low-level IO error

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

openIfChanged

public static DirectoryReader openIfChanged(DirectoryReader oldReader,
                                            IndexWriter writer,
                                            boolean applyAllDeletes)
                                     throws IOException

Expert: Opens a new reader, if there are any changes, controlling whether past deletions should be applied.

Parameters:

writer - The IndexWriter to open from

applyAllDeletes - If true, all buffered deletes will be applied (made visible) in the returned reader. If false, the deletes are not applied but remain buffered (in IndexWriter) so that they will be applied in the future. Applying deletes can be costly, so if your app can tolerate deleted documents being returned you might gain some performance by passing false.

Throws:

IOException - if there is a low-level IO error

See Also:

openIfChanged(DirectoryReader,IndexWriter)

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

listCommits

public static List<IndexCommit> listCommits(Directory dir)
                                     throws IOException

Returns all commit points that exist in the Directory. Normally, because the default is KeepOnlyLastCommitDeletionPolicy, there would be only one commit point. But if you're using a custom IndexDeletionPolicy then there could be many commits. Once you have a given commit, you can open a reader on it by calling open(IndexCommit) There must be at least one commit in the Directory, else this method throws IndexNotFoundException. Note that if a commit is in progress while this method is running, that commit may or may not be returned.

Returns:

a sorted list of IndexCommits, from oldest to latest.

Throws:

IOException

indexExists

public static boolean indexExists(Directory directory)
                           throws IOException

Returns true if an index likely exists at the specified directory. Note that if a corrupt index exists, or if an index in the process of committing

Parameters:

directory - the directory to check for an index

Returns:

true if an index exists; false otherwise

Throws:

IOException

directory

public final Directory directory()

Returns the directory this index resides in.

doOpenIfChanged

protected abstract DirectoryReader doOpenIfChanged()
                                            throws IOException

Implement this method to support openIfChanged(DirectoryReader). If this reader does not support reopen, return null, so client code is happy. This should be consistent with isCurrent() (should always return true) if reopen is not supported.

Returns:

null if there are no changes; else, a new DirectoryReader instance.

Throws:

IOException - if there is a low-level IO error

doOpenIfChanged

protected abstract DirectoryReader doOpenIfChanged(IndexCommit commit)
                                            throws IOException

Implement this method to support openIfChanged(DirectoryReader,IndexCommit). If this reader does not support reopen from a specific IndexCommit, throw UnsupportedOperationException.

Returns:

null if there are no changes; else, a new DirectoryReader instance.

Throws:

IOException - if there is a low-level IO error

doOpenIfChanged

protected abstract DirectoryReader doOpenIfChanged(IndexWriter writer,
                                                   boolean applyAllDeletes)
                                            throws IOException

Implement this method to support openIfChanged(DirectoryReader,IndexWriter,boolean). If this reader does not support reopen from IndexWriter, throw UnsupportedOperationException.

Returns:

null if there are no changes; else, a new DirectoryReader instance.

Throws:

IOException - if there is a low-level IO error

getVersion

public abstract long getVersion()

Version number when this IndexReader was opened.

This method returns the version recorded in the commit that the reader opened. This version is advanced every time a change is made with IndexWriter.

isCurrent

public abstract boolean isCurrent()
                           throws IOException

Check whether any new changes have occurred to the index since this reader was opened.

If this reader was created by calling open(org.apache.lucene.store.Directory), then this method checks if any further commits (see IndexWriter.commit()) have occurred in the directory.

If instead this reader is a near real-time reader (ie, obtained by a call to open(IndexWriter), or by calling openIfChanged(org.apache.lucene.index.DirectoryReader) on a near real-time reader), then this method checks if either a new commit has occurred, or any new uncommitted changes have taken place via the writer. Note that even if the writer has only performed merging, this method will still return false.

In any event, if this returns false, you should call openIfChanged(org.apache.lucene.index.DirectoryReader) to get a new reader that sees the changes.

Throws:

IOException - if there is a low-level IO error

getIndexCommit

public abstract IndexCommit getIndexCommit()
                                    throws IOException

Expert: return the IndexCommit that this reader has opened.

Throws:

IOException

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