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org.apache.lucene.index
public class: IndexWriter [javadoc | source]
java.lang.Object
   org.apache.lucene.index.IndexWriter

All Implemented Interfaces:
    Closeable

An IndexWriter creates and maintains an index.

The create argument to the constructor determines whether a new index is created, or whether an existing index is opened. Note that you can open an index with create=true 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. There are also constructors with no create argument which 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 and removed with #deleteDocuments(Term) or #deleteDocuments(Query) . A document can be updated with updateDocument (which just deletes and then adds the entire document). When finished adding, deleting and updating documents, close 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 buffered deletes (see #setMaxBufferedDeleteTerms ) or enough added documents since the last flush, whichever is sooner. For the added documents, flushing is triggered either by RAM usage of the documents (see #setRAMBufferSizeMB ) or the number of added documents. The default is to flush when RAM usage hits 16 MB. For best indexing speed you should flush by RAM usage with a large RAM buffer. 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 #close 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 MergeScheduler ).

If an index will not have more documents added for a while and optimal search performance is desired, then either the full optimize method or partial #optimize(int) method should be called before the index is closed.

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 MergePolicy and the MergeScheduler . The 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. It also selects merges to do for optimize(). (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 OutOfMemoryError 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 IllegalStateException. The only course of action is to call #close() , 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: If you call Thread.interrupt() on a thread that's within IndexWriter, IndexWriter will try to catch this (eg, if it's in a wait() or Thread.sleep()), and will then throw the unchecked exception ThreadInterruptedException and clear the interrupt status on the thread.

Nested Class Summary:
class  IndexWriter.ReaderPool  Holds shared SegmentReader instances. IndexWriter uses SegmentReaders for 1) applying deletes, 2) doing merges, 3) handing out a real-time reader. This pool reuses instances of the SegmentReaders in all these places if it is in "near real-time mode" (getReader() has been called on this instance). 
public static final class  IndexWriter.MaxFieldLength  Specifies maximum field length (in number of tokens/terms) in {@link IndexWriter} constructors. {@link #setMaxFieldLength(int)} overrides the value set by the constructor. 
abstract public static class  IndexWriter.IndexReaderWarmer  If {@link #getReader} has been called (ie, this writer is in near real-time mode), then after a merge completes, this class can be invoked to warm the reader on the newly merged segment, before the merge commits. This is not required for near real-time search, but will reduce search latency on opening a new near real-time reader after a merge completes.

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

NOTE: warm is called before any deletes have been carried over to the merged segment. 

Field Summary
public static  long WRITE_LOCK_TIMEOUT    Default value for the write lock timeout (1,000). 
public static final  String WRITE_LOCK_NAME    Name of the write lock in the index. 
public static final  int DISABLE_AUTO_FLUSH    Value to denote a flush trigger is disabled 
public static final  int DEFAULT_MAX_BUFFERED_DOCS    Disabled by default (because IndexWriter flushes by RAM usage by default). Change using #setMaxBufferedDocs(int)
public static final  double DEFAULT_RAM_BUFFER_SIZE_MB    Default value is 16 MB (which means flush when buffered docs consume 16 MB RAM). Change using #setRAMBufferSizeMB
public static final  int DEFAULT_MAX_BUFFERED_DELETE_TERMS    Disabled by default (because IndexWriter flushes by RAM usage by default). Change using #setMaxBufferedDeleteTerms(int)
public static final  int DEFAULT_MAX_FIELD_LENGTH    Default value is 10,000. Change using #setMaxFieldLength(int)
public static final  int DEFAULT_TERM_INDEX_INTERVAL    Default value is 128. Change using #setTermIndexInterval(int)
public static final  int MAX_TERM_LENGTH    Absolute hard maximum length for a term. If a term arrives from the analyzer longer than this length, it is skipped and a message is printed to infoStream, if set (see #setInfoStream ). 
volatile  SegmentInfos pendingCommit     
volatile  long pendingCommitChangeCount     
final  ReaderPool readerPool     
Constructor:
 public IndexWriter(Directory d,
    Analyzer a,
    MaxFieldLength mfl) throws CorruptIndexException, LockObtainFailedException, IOException 
    Constructs an IndexWriter for the index in d, first creating it if it does not already exist. Text will be analyzed with a.
    Parameters:
    d - the index directory
    a - the analyzer to use
    mfl - Maximum field length in number of terms/tokens: LIMITED, UNLIMITED, or user-specified via the MaxFieldLength constructor.
    Throws:
    CorruptIndexException - if the index is corrupt
    LockObtainFailedException - if another writer has this index open (write.lock could not be obtained)
    IOException - if the directory cannot be read/written to or if there is any other low-level IO error
 public IndexWriter(Directory d,
    Analyzer a,
    boolean create,
    MaxFieldLength mfl) throws CorruptIndexException, LockObtainFailedException, IOException 
    Constructs an IndexWriter for the index in d. Text will be analyzed with a. If create is true, then a new, empty index will be created in d, replacing the index already there, if any.
    Parameters:
    d - the index directory
    a - the analyzer to use
    create - true to create the index or overwrite the existing one; false to append to the existing index
    mfl - Maximum field length in number of terms/tokens: LIMITED, UNLIMITED, or user-specified via the MaxFieldLength constructor.
    Throws:
    CorruptIndexException - if the index is corrupt
    LockObtainFailedException - if another writer has this index open (write.lock could not be obtained)
    IOException - if the directory cannot be read/written to, or if it does not exist and create is false or if there is any other low-level IO error
 public IndexWriter(Directory d,
    Analyzer a,
    IndexDeletionPolicy deletionPolicy,
    MaxFieldLength mfl) throws CorruptIndexException, LockObtainFailedException, IOException 
    Expert: constructs an IndexWriter with a custom IndexDeletionPolicy , for the index in d, first creating it if it does not already exist. Text will be analyzed with a.
    Parameters:
    d - the index directory
    a - the analyzer to use
    deletionPolicy - see above
    mfl - whether or not to limit field lengths
    Throws:
    CorruptIndexException - if the index is corrupt
    LockObtainFailedException - if another writer has this index open (write.lock could not be obtained)
    IOException - if the directory cannot be read/written to or if there is any other low-level IO error
 public IndexWriter(Directory d,
    Analyzer a,
    boolean create,
    IndexDeletionPolicy deletionPolicy,
    MaxFieldLength mfl) throws CorruptIndexException, LockObtainFailedException, IOException 
    Expert: constructs an IndexWriter with a custom IndexDeletionPolicy , for the index in d. Text will be analyzed with a. If create is true, then a new, empty index will be created in d, replacing the index already there, if any.
    Parameters:
    d - the index directory
    a - the analyzer to use
    create - true to create the index or overwrite the existing one; false to append to the existing index
    deletionPolicy - see above
    mfl - org.apache.lucene.index.IndexWriter.MaxFieldLength , whether or not to limit field lengths. Value is in number of terms/tokens
    Throws:
    CorruptIndexException - if the index is corrupt
    LockObtainFailedException - if another writer has this index open (write.lock could not be obtained)
    IOException - if the directory cannot be read/written to, or if it does not exist and create is false or if there is any other low-level IO error
 public IndexWriter(Directory d,
    Analyzer a,
    IndexDeletionPolicy deletionPolicy,
    MaxFieldLength mfl,
    IndexCommit commit) throws CorruptIndexException, LockObtainFailedException, IOException 
    Expert: constructs an IndexWriter on specific commit point, with a custom IndexDeletionPolicy , for the index in d. Text will be analyzed with a.

    This is only meaningful if you've used a IndexDeletionPolicy in that past that keeps more than just the last commit.

    This operation is similar to #rollback() , except that method can only rollback what's been done with the current instance of IndexWriter since its last commit, whereas this method can rollback to an arbitrary commit point from the past, assuming the IndexDeletionPolicy has preserved past commits.

    Parameters:
    d - the index directory
    a - the analyzer to use
    deletionPolicy - see above
    mfl - whether or not to limit field lengths, value is in number of terms/tokens. See org.apache.lucene.index.IndexWriter.MaxFieldLength .
    commit - which commit to open
    Throws:
    CorruptIndexException - if the index is corrupt
    LockObtainFailedException - if another writer has this index open (write.lock could not be obtained)
    IOException - if the directory cannot be read/written to, or if it does not exist and create is false or if there is any other low-level IO error
 IndexWriter(Directory d,
    Analyzer a,
    boolean create,
    IndexDeletionPolicy deletionPolicy,
    MaxFieldLength mfl,
    IndexingChain indexingChain,
    IndexCommit commit) throws CorruptIndexException, LockObtainFailedException, IOException 
    Expert: constructs an IndexWriter with a custom IndexDeletionPolicy and IndexingChain , for the index in d. Text will be analyzed with a. If create is true, then a new, empty index will be created in d, replacing the index already there, if any.
    Parameters:
    d - the index directory
    a - the analyzer to use
    create - true to create the index or overwrite the existing one; false to append to the existing index
    deletionPolicy - see above
    mfl - whether or not to limit field lengths, value is in number of terms/tokens. See org.apache.lucene.index.IndexWriter.MaxFieldLength .
    indexingChain - the DocConsumer chain to be used to process documents
    commit - which commit to open
    Throws:
    CorruptIndexException - if the index is corrupt
    LockObtainFailedException - if another writer has this index open (write.lock could not be obtained)
    IOException - if the directory cannot be read/written to, or if it does not exist and create is false or if there is any other low-level IO error
Method from org.apache.lucene.index.IndexWriter Summary:
acquireRead,   acquireWrite,   addDocument,   addDocument,   addIndexes,   addIndexesNoOptimize,   addMergeException,   close,   close,   commit,   commit,   deleteAll,   deleteDocuments,   deleteDocuments,   deleteDocuments,   deleteDocuments,   doAfterFlush,   ensureOpen,   ensureOpen,   expungeDeletes,   expungeDeletes,   flush,   getAnalyzer,   getBufferedDeleteTermsSize,   getDefaultInfoStream,   getDefaultWriteLockTimeout,   getDirectory,   getDocCount,   getFlushCount,   getFlushDeletesCount,   getInfoStream,   getMaxBufferedDeleteTerms,   getMaxBufferedDocs,   getMaxFieldLength,   getMaxMergeDocs,   getMergeFactor,   getMergePolicy,   getMergeScheduler,   getMergedSegmentWarmer,   getNextMerge,   getNumBufferedDeleteTerms,   getNumBufferedDocuments,   getRAMBufferSizeMB,   getReader,   getReader,   getSegmentCount,   getSimilarity,   getTermIndexInterval,   getUseCompoundFile,   getWriteLockTimeout,   hasDeletions,   isClosed,   isLocked,   isOpen,   maxDoc,   maybeMerge,   merge,   mergeFinish,   mergeInit,   mergeSuccess,   message,   newSegmentName,   newestSegment,   nrtIsCurrent,   numDeletedDocs,   numDocs,   numRamDocs,   optimize,   optimize,   optimize,   optimize,   prepareCommit,   prepareCommit,   ramSizeInBytes,   registerMerge,   releaseRead,   releaseWrite,   rollback,   segString,   setDefaultInfoStream,   setDefaultWriteLockTimeout,   setInfoStream,   setMaxBufferedDeleteTerms,   setMaxBufferedDocs,   setMaxFieldLength,   setMaxMergeDocs,   setMergeFactor,   setMergePolicy,   setMergeScheduler,   setMergedSegmentWarmer,   setRAMBufferSizeMB,   setSimilarity,   setTermIndexInterval,   setUseCompoundFile,   setWriteLockTimeout,   testPoint,   unlock,   updateDocument,   updateDocument,   upgradeReadToWrite,   verbose,   waitForMerges
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from org.apache.lucene.index.IndexWriter Detail:
 synchronized  void acquireRead() 
 synchronized  void acquireWrite() 
 public  void addDocument(Document doc) throws CorruptIndexException, IOException 
    Adds a document to this index. If the document contains more than #setMaxFieldLength(int) terms for a given field, the remainder are discarded.

    Note that if an 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 above), 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 #optimize() 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 16383 characters, otherwise an IllegalArgumentException 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 OutOfMemoryError you should immediately close the writer. See above for details.

 public  void addDocument(Document doc,
    Analyzer analyzer) throws CorruptIndexException, IOException 
    Adds a document to this index, using the provided analyzer instead of the value of #getAnalyzer() . If the document contains more than #setMaxFieldLength(int) terms for a given field, the remainder are discarded.

    See #addDocument(Document) for details on index and IndexWriter state after an Exception, and flushing/merging temporary free space requirements.

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public  void addIndexes(IndexReader readers) throws CorruptIndexException, IOException 
    Merges the provided indexes into this index.

    After this completes, the index is optimized.

    The provided IndexReaders are not closed.

    NOTE: while this is running, any attempts to add or delete documents (with another thread) will be paused until this method completes.

    See #addIndexesNoOptimize for details on transactional semantics, temporary free space required in the Directory, and non-CFS segments on an Exception.

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public  void addIndexesNoOptimize(Directory dirs) throws CorruptIndexException, IOException 
    Merges 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: the index in each Directory must not be changed (opened by a writer) while this method is running. This method does not acquire a write lock in each input Directory, so it is up to the caller to enforce this.

    NOTE: while this is running, any attempts to add or delete documents (with another thread) will be paused until this method completes.

    This method is transactional in how Exceptions are handled: it does not commit a new segments_N file until all indexes are added. This means if an 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 #optimize() for details).

    Once this completes, the final size of the index will be less than the sum of all input index sizes (including the starting index). It could be quite a bit smaller (if there were many pending deletes) or just slightly smaller.

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

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 synchronized  void addMergeException(OneMerge merge) 
 public  void close() throws CorruptIndexException, IOException 
    Commits all changes to an index and closes all associated files. 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 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 close() 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.close();
    } 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 OutOfMemoryError you should immediately close the writer, again. See above for details.

 public  void close(boolean waitForMerges) throws CorruptIndexException, IOException 
    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 OutOfMemoryError you should immediately close the writer, again. See above for details.

    NOTE: it is dangerous to always call close(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.

 public final  void commit() throws CorruptIndexException, IOException 

    Commits all pending changes (added & deleted documents, optimizations, 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 Directory.sync 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 OutOfMemoryError you should immediately close the writer. See above for details.

 public final  void commit(Map<String, String> commitUserData) throws CorruptIndexException, IOException 
    Commits all changes to the index, specifying a commitUserData Map (String -> String). This just calls #prepareCommit(Map) (if you didn't already call it) and then #finishCommit .

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public synchronized  void deleteAll() throws IOException 
    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() ).

    NOTE: this method will forcefully abort all merges in progress. If other threads are running #optimize() or any of the addIndexes methods, they will receive MergePolicy.MergeAbortedException s.

 public  void deleteDocuments(Term term) throws CorruptIndexException, IOException 
    Deletes the document(s) containing term.

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public  void deleteDocuments(Term terms) throws CorruptIndexException, IOException 
    Deletes the document(s) containing any of the terms. All deletes are flushed at the same time.

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public  void deleteDocuments(Query query) throws CorruptIndexException, IOException 
    Deletes the document(s) matching the provided query.

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public  void deleteDocuments(Query queries) throws CorruptIndexException, IOException 
    Deletes the document(s) matching any of the provided queries. All deletes are flushed at the same time.

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

  void doAfterFlush() throws IOException 
 protected final synchronized  void ensureOpen() throws AlreadyClosedException 
 protected final synchronized  void ensureOpen(boolean includePendingClose) throws AlreadyClosedException 
 public  void expungeDeletes() throws CorruptIndexException, IOException 
    Expunges all deletes from the index. When an index has many document deletions (or updates to existing documents), it's best to either call optimize or expungeDeletes to remove all unused data in the index associated with the deleted documents. To see how many deletions you have pending in your index, call IndexReader#numDeletedDocs This saves disk space and memory usage while searching. expungeDeletes should be somewhat faster than optimize since it does not insist on reducing the index to a single segment (though, this depends on the MergePolicy ; see MergePolicy#findMergesToExpungeDeletes .). Note that this call does not first commit any buffered documents, so you must do so yourself if necessary. See also #expungeDeletes(boolean)

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public  void expungeDeletes(boolean doWait) throws CorruptIndexException, IOException 
    Just like #expungeDeletes() , 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 OutOfMemoryError you should immediately close the writer. See above for details.

 protected final  void flush(boolean triggerMerge,
    boolean flushDocStores,
    boolean flushDeletes) throws CorruptIndexException, IOException 
    Flush all in-memory buffered udpates (adds and deletes) to the Directory.
 public Analyzer getAnalyzer() 
    Returns the analyzer used by this index.
 final synchronized int getBufferedDeleteTermsSize() 
 public static PrintStream getDefaultInfoStream() 
    Returns the current default infoStream for newly instantiated IndexWriters.
 public static long getDefaultWriteLockTimeout() 
    Returns default write lock timeout for newly instantiated IndexWriters.
 public Directory getDirectory() 
    Returns the Directory used by this index.
 final synchronized int getDocCount(int i) 
 final synchronized int getFlushCount() 
 final synchronized int getFlushDeletesCount() 
 public PrintStream getInfoStream() 
    Returns the current infoStream in use by this writer.
 public int getMaxBufferedDeleteTerms() 
    Returns the number of buffered deleted terms that will trigger a flush if enabled.
 public int getMaxBufferedDocs() 
    Returns the number of buffered added documents that will trigger a flush if enabled.
 public int getMaxFieldLength() 
    Returns the maximum number of terms that will be indexed for a single field in a document.
 public int getMaxMergeDocs() 

    Returns the largest segment (measured by document count) that may be merged with other segments.

    Note that this method is a convenience method: it just calls mergePolicy.getMaxMergeDocs as long as mergePolicy is an instance of LogMergePolicy . Otherwise an IllegalArgumentException is thrown.

 public int getMergeFactor() 

    Returns the number of segments that are merged at once and also controls the total number of segments allowed to accumulate in the index.

    Note that this method is a convenience method: it just calls mergePolicy.getMergeFactor as long as mergePolicy is an instance of LogMergePolicy . Otherwise an IllegalArgumentException is thrown.

 public MergePolicy getMergePolicy() 
    Expert: returns the current MergePolicy in use by this writer.
 public MergeScheduler getMergeScheduler() 
    Expert: returns the current MergePolicy in use by this writer.
 public IndexReaderWarmer getMergedSegmentWarmer() 
 synchronized OneMerge getNextMerge() 
    Expert: the MergeScheduler calls this method to retrieve the next merge requested by the MergePolicy
 final synchronized int getNumBufferedDeleteTerms() 
 final synchronized int getNumBufferedDocuments() 
 public double getRAMBufferSizeMB() 
 public IndexReader getReader() throws IOException 
    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 {#commit} and then using IndexReader#open to open a new reader. But the turarnound 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 IndexReader#reopen , 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 call #setMergedSegmentWarmer 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 .

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

 public IndexReader getReader(int termInfosIndexDivisor) throws IOException 
    Expert: like #getReader , except you can specify which termInfosIndexDivisor should be used for any newly opened readers.
 final synchronized int getSegmentCount() 
 public Similarity getSimilarity() 
    Expert: Return the Similarity implementation used by this IndexWriter.

    This defaults to the current value of Similarity#getDefault() .

 public int getTermIndexInterval() 
    Expert: Return the interval between indexed terms.
 public boolean getUseCompoundFile() 

    Get the current setting of whether newly flushed segments will use the compound file format. Note that this just returns the value previously set with setUseCompoundFile(boolean), or the default value (true). You cannot use this to query the status of previously flushed segments.

    Note that this method is a convenience method: it just calls mergePolicy.getUseCompoundFile as long as mergePolicy is an instance of LogMergePolicy . Otherwise an IllegalArgumentException is thrown.

 public long getWriteLockTimeout() 
    Returns allowed timeout when acquiring the write lock.
 public synchronized boolean hasDeletions() throws IOException 
 synchronized boolean isClosed() 
 public static boolean isLocked(Directory directory) throws IOException 
    Returns true iff the index in the named directory is currently locked.
 final synchronized boolean isOpen(boolean includePendingClose) 
 public synchronized int maxDoc() 
    Returns total number of docs in this index, including docs not yet flushed (still in the RAM buffer), not counting deletions.
 public final  void maybeMerge() throws CorruptIndexException, IOException 
    Expert: asks the 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 mergePolicy. Explicit calls to maybeMerge() are usually not necessary. The most common case is when merge policy parameters have changed.

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 final  void merge(OneMerge merge) throws CorruptIndexException, IOException 
    Merges the indicated segments, replacing them in the stack with a single segment.
 final synchronized  void mergeFinish(OneMerge merge) throws IOException 
    Does fininishing for a merge, which is fast but holds the synchronized lock on IndexWriter instance.
 final synchronized  void mergeInit(OneMerge merge) throws IOException 
    Does initial setup for a merge, which is fast but holds the synchronized lock on IndexWriter instance.
  void mergeSuccess(OneMerge merge) 
    Hook that's called when the specified merge is complete.
 public  void message(String message) 
    Prints a message to the infoStream (if non-null), prefixed with the identifying information for this writer and the thread that's calling it.
 final String newSegmentName() 
 SegmentInfo newestSegment() 
 synchronized boolean nrtIsCurrent(SegmentInfos infos) 
 public int numDeletedDocs(SegmentInfo info) throws IOException 
    Obtain the number of deleted docs for a pooled reader. If the reader isn't being pooled, the segmentInfo's delCount is returned.
 public synchronized int numDocs() throws IOException 
    Returns 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.
 public final synchronized int numRamDocs() 
    Expert: Return the number of documents currently buffered in RAM.
 public  void optimize() throws CorruptIndexException, IOException 
    Requests an "optimize" operation on an index, priming the index for the fastest available search. Traditionally this has meant merging all segments into a single segment as is done in the default merge policy, but individual merge policies may implement optimize in different ways.

    It is recommended that this method be called upon completion of indexing. In environments with frequent updates, optimize is best done during low volume times, if at all.

    See http://www.gossamer-threads.com/lists/lucene/java-dev/47895 for more discussion.

    Note that optimize requires 2X the index size free space in your Directory. For example, if your index size is 10 MB then you need 20 MB free for optimize to complete.

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

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

    In general, once the optimize 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 Exception is hit during optimize(), for example due to disk full, the index will not be corrupt and no documents will have been lost. However, it may have been partially optimized (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 Exception is hit during conversion of the segment into compound format.

    This call will optimize 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 optimized unless you call optimize again.

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public  void optimize(int maxNumSegments) throws CorruptIndexException, IOException 
    Optimize the index down to <= maxNumSegments. If maxNumSegments==1 then this is the same as #optimize() .

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public  void optimize(boolean doWait) throws CorruptIndexException, IOException 
    Just like #optimize() , except you can specify whether the call should block until the optimize completes. This is only meaningful with a MergeScheduler that is able to run merges in background threads.

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public  void optimize(int maxNumSegments,
    boolean doWait) throws CorruptIndexException, IOException 
    Just like #optimize(int) , except you can specify whether the call should block until the optimize completes. This is only meaningful with a MergeScheduler that is able to run merges in background threads.

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public final  void prepareCommit() throws CorruptIndexException, IOException 
    Expert: prepare for commit.

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public final  void prepareCommit(Map<String, String> commitUserData) throws CorruptIndexException, IOException 

    Expert: prepare for commit, specifying commitUserData Map (String -> String). 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(Map) directly without prepareCommit first in which case that method will internally call prepareCommit.

    NOTE: if this method hits an OutOfMemoryError you should immediately close the writer. See above for details.

 public final long ramSizeInBytes() 
    Expert: Return the total size of all index files currently cached in memory. Useful for size management with flushRamDocs()
 final synchronized boolean registerMerge(OneMerge merge) throws MergeAbortedException 
    Checks whether this merge involves any segments already participating in a merge. If not, this merge is "registered", meaning we record that its segments are now participating in a merge, and true is returned. Else (the merge conflicts) false is returned.
 synchronized  void releaseRead() 
 synchronized  void releaseWrite() 
 public  void rollback() throws IOException 
    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 .
 public synchronized String segString() 
 public static  void setDefaultInfoStream(PrintStream infoStream) 
    If non-null, this will be the default infoStream used by a newly instantiated IndexWriter.
 public static  void setDefaultWriteLockTimeout(long writeLockTimeout) 
    Sets the default (for any instance of IndexWriter) maximum time to wait for a write lock (in milliseconds).
 public  void setInfoStream(PrintStream infoStream) 
    If non-null, information about merges, deletes and a message when maxFieldLength is reached will be printed to this.
 public  void setMaxBufferedDeleteTerms(int maxBufferedDeleteTerms) 

    Determines the minimal number of delete terms required before the buffered in-memory delete terms are applied and flushed. If there are documents buffered in memory at the time, they are merged and a new segment is created.

    Disabled by default (writer flushes by RAM usage).

 public  void setMaxBufferedDocs(int maxBufferedDocs) 
    Determines the minimal number of documents required before the buffered in-memory documents are flushed as a new Segment. Large values generally gives faster indexing.

    When this is set, the writer will flush every maxBufferedDocs added documents. Pass in #DISABLE_AUTO_FLUSH to prevent triggering a flush due to number of buffered documents. Note that if flushing by RAM usage is also enabled, then the flush will be triggered by whichever comes first.

    Disabled by default (writer flushes by RAM usage).

 public  void setMaxFieldLength(int maxFieldLength) 
    The maximum number of terms that will be indexed for a single field in a document. This limits the amount of memory required for indexing, so that collections with very large files will not crash the indexing process by running out of memory. This setting refers to the number of running terms, not to the number of different terms.

    Note: this silently truncates large documents, excluding from the index all terms that occur further in the document. If you know your source documents are large, be sure to set this value high enough to accomodate the expected size. If you set it to Integer.MAX_VALUE, then the only limit is your memory, but you should anticipate an OutOfMemoryError.

    By default, no more than #DEFAULT_MAX_FIELD_LENGTH terms will be indexed for a field.

 public  void setMaxMergeDocs(int maxMergeDocs) 

    Determines the largest segment (measured by document count) that may be merged with other segments. Small values (e.g., less than 10,000) are best for interactive indexing, as this limits the length of pauses while indexing to a few seconds. Larger values are best for batched indexing and speedier searches.

    The default value is Integer#MAX_VALUE .

    Note that this method is a convenience method: it just calls mergePolicy.setMaxMergeDocs as long as mergePolicy is an instance of LogMergePolicy . Otherwise an IllegalArgumentException is thrown.

    The default merge policy (LogByteSizeMergePolicy ) also allows you to set this limit by net size (in MB) of the segment, using LogByteSizeMergePolicy#setMaxMergeMB .

 public  void setMergeFactor(int mergeFactor) 
    Determines how often segment indices are merged by addDocument(). With smaller values, less RAM is used while indexing, and searches on unoptimized indices are faster, but indexing speed is slower. With larger values, more RAM is used during indexing, and while searches on unoptimized indices are slower, indexing is faster. Thus larger values (> 10) are best for batch index creation, and smaller values (< 10) for indices that are interactively maintained.

    Note that this method is a convenience method: it just calls mergePolicy.setMergeFactor as long as mergePolicy is an instance of LogMergePolicy . Otherwise an IllegalArgumentException is thrown.

    This must never be less than 2. The default value is 10.

 public  void setMergePolicy(MergePolicy mp) 
    Expert: set the merge policy used by this writer.
 public synchronized  void setMergeScheduler(MergeScheduler mergeScheduler) throws CorruptIndexException, IOException 
    Expert: set the merge scheduler used by this writer.
 public  void setMergedSegmentWarmer(IndexReaderWarmer warmer) 
 public  void setRAMBufferSizeMB(double mb) 
    Determines the amount of RAM that may be used for buffering added documents and deletions before they are flushed to the Directory. Generally for faster indexing performance it's best to flush by RAM usage instead of document count and use as large a RAM buffer as you can.

    When this is set, the writer will flush whenever buffered documents and deletions use this much RAM. Pass in #DISABLE_AUTO_FLUSH to prevent triggering a flush due to RAM usage. Note that if flushing by document count is also enabled, then the flush will be triggered by whichever comes first.

    NOTE: the account of RAM usage for pending deletions is only approximate. Specifically, if you delete by Query, Lucene currently has no way to measure the RAM usage if individual Queries so the accounting will under-estimate and you should compensate by either calling commit() periodically yourself, or by using #setMaxBufferedDeleteTerms to flush by count instead of RAM usage (each buffered delete Query counts as one).

    NOTE: because IndexWriter uses ints when managing its internal storage, the absolute maximum value for this setting is somewhat less than 2048 MB. The precise limit depends on various factors, such as how large your documents are, how many fields have norms, etc., so it's best to set this value comfortably under 2048.

    The default value is #DEFAULT_RAM_BUFFER_SIZE_MB .

 public  void setSimilarity(Similarity similarity) 
    Expert: Set the Similarity implementation used by this IndexWriter.
 public  void setTermIndexInterval(int interval) 
    Expert: Set the interval between indexed terms. Large values cause less memory to be used by IndexReader, but slow random-access to terms. Small values cause more memory to be used by an IndexReader, and speed random-access to terms. This parameter determines the amount of computation required per query term, regardless of the number of documents that contain that term. In particular, it is the maximum number of other terms that must be scanned before a term is located and its frequency and position information may be processed. In a large index with user-entered query terms, query processing time is likely to be dominated not by term lookup but rather by the processing of frequency and positional data. In a small index or when many uncommon query terms are generated (e.g., by wildcard queries) term lookup may become a dominant cost. In particular, numUniqueTerms/interval terms are read into memory by an IndexReader, and, on average, interval/2 terms must be scanned for each random term access.
 public  void setUseCompoundFile(boolean value) 

    Setting to turn on usage of a compound file. When on, multiple files for each segment are merged into a single file when a new segment is flushed.

    Note that this method is a convenience method: it just calls mergePolicy.setUseCompoundFile as long as mergePolicy is an instance of LogMergePolicy . Otherwise an IllegalArgumentException is thrown.

 public  void setWriteLockTimeout(long writeLockTimeout) 
    Sets the maximum time to wait for a write lock (in milliseconds) for this instance of IndexWriter. @see
 boolean testPoint(String name) 
 public static  void unlock(Directory directory) throws IOException 
    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.

 public  void updateDocument(Term term,
    Document doc) throws CorruptIndexException, IOException 
    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 OutOfMemoryError you should immediately close the writer. See above for details.

 public  void updateDocument(Term term,
    Document doc,
    Analyzer analyzer) throws CorruptIndexException, IOException 
    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 OutOfMemoryError you should immediately close the writer. See above for details.

 synchronized  void upgradeReadToWrite() 
 public boolean verbose() 
    Returns true if verbosing is enabled (i.e., infoStream != null).
 public synchronized  void 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.