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 {@link 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 {@link #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.

See {@link #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.

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

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 {@link #AddIndexesNoOptimize(Directory[])} 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.

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 {@link #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.

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);
            }
            }
            

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

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.

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.

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

This method will drop all buffered documents and will remove all segments from the index. This change will not be visible until a {@link #Commit()} has been called. This method can be rolled back using {@link #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 {@link #Optimize()} or any of the addIndexes methods, they will receive {@link MergePolicy.MergeAbortedException}s.

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

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

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

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

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

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

Note: while this will force buffered docs to be pushed into the index, it will not make these docs visible to a reader. Use {@link #Commit()} instead

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

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 {@link LogMergePolicy}. Otherwise an IllegalArgumentException is thrown.

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 {@link LogMergePolicy}. Otherwise an IllegalArgumentException is thrown.

Note that this is functionally equivalent to calling {#commit} and then using {@link IndexReader#open} to open a new reader. But the turarnound time of this method should be faster since it avoids the potentially costly {@link #commit}.

You must close the {@link 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 faster 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 suppports {@link 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 {@link #setMergedSegmentWarmer} to call {@link #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 {@link AlreadyClosedException}.

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

This defaults to the current value of {@link Similarity#GetDefault()}.

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 {@link LogMergePolicy}. Otherwise an IllegalArgumentException is thrown.

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

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 (3X if you're using compound file format). For example, if your index size is 10 MB then you need 20 MB free for optimize to complete (30 MB if you're using compound fiel format).

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.

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

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

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

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

Expert: prepare for commit, specifying commitUserData Map (String -> String). This does the first phase of 2-phase commit. You can only call this when autoCommit is false. 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 {@link #Commit()} to finish the commit, or {@link #Rollback()} to revert the commit and undo all changes done since the writer was opened.

You can also just call {@link #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.

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).

When this is set, the writer will flush every maxBufferedDocs added documents. Pass in {@link #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).

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 {@link #DEFAULT_MAX_FIELD_LENGTH} terms will be indexed for a field.

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 {@link Integer#MAX_VALUE}.

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

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

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

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

When this is set, the writer will flush whenever buffered documents and deletions use this much RAM. Pass in {@link #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 {@link #setMaxBufferedDeleteTerms} to flush by count instead of RAM usage (each buffered delete Query counts as one).

NOTE: because IndexWriter uses

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The default value is {@link #DEFAULT_RAM_BUFFER_SIZE_MB}.

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 {@link LogMergePolicy}. Otherwise an IllegalArgumentException is thrown.

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.

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

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

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