An IndexWriter creates and maintains an index.
The third argument (
create
) to the
constructor
determines whether a new index is created, or whether an existing index is
opened for the addition of new documents. 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.
In either case, documents are added with the
addDocument method.
When finished adding documents,
close should be called.
If an index will not have more documents added for a while and optimal search
performance is desired, then the
optimize
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 an IOException. The IOException
is also thrown if an IndexReader on the same directory is used to delete documents
from the index.
As of
2.1, IndexWriter can now delete documents
by
Term
(see
deleteDocuments
) and update
(delete then add) documents (see
updateDocument
).
Deletes are buffered until
setMaxBufferedDeleteTerms(int)
Terms
at which
point they are flushed to the index. Note that a flush
occurs when there are enough buffered deletes or enough
added documents, whichever is sooner. When a flush
occurs, both pending deletes and added documents are
flushed to the index.
DEFAULT_MAX_BUFFERED_DELETE_TERMS
public static final int DEFAULT_MAX_BUFFERED_DELETE_TERMS
DEFAULT_MAX_BUFFERED_DOCS
public static final int DEFAULT_MAX_BUFFERED_DOCS
DEFAULT_MAX_FIELD_LENGTH
public static final int DEFAULT_MAX_FIELD_LENGTH
DEFAULT_MAX_MERGE_DOCS
public static final int DEFAULT_MAX_MERGE_DOCS
DEFAULT_MERGE_FACTOR
public static final int DEFAULT_MERGE_FACTOR
DEFAULT_TERM_INDEX_INTERVAL
public static final int DEFAULT_TERM_INDEX_INTERVAL
WRITE_LOCK_NAME
public static final String WRITE_LOCK_NAME
WRITE_LOCK_TIMEOUT
public static long WRITE_LOCK_TIMEOUT
Default value for the write lock timeout (1,000).
IndexWriter
public IndexWriter(File path,
Analyzer a)
throws IOException
Constructs an IndexWriter for the index in
path
, creating it first if it does not
already exist, otherwise appending to the existing
index. Text will be analyzed with
a
.
path
- the path to the index directorya
- the analyzer to use
IndexWriter
public IndexWriter(File path,
Analyzer a,
boolean create)
throws IOException
Constructs an IndexWriter for the index in path
.
Text will be analyzed with a
. If create
is true, then a new, empty index will be created in
path
, replacing the index already there, if any.
path
- the path to the index directorya
- the analyzer to usecreate
- true
to create the index or overwrite
the existing one; false
to append to the existing
index
IndexWriter
public IndexWriter(String path,
Analyzer a)
throws IOException
Constructs an IndexWriter for the index in
path
, creating it first if it does not
already exist, otherwise appending to the existing
index. Text will be analyzed with a
.
path
- the path to the index directorya
- the analyzer to use
IndexWriter
public IndexWriter(String path,
Analyzer a,
boolean create)
throws IOException
Constructs an IndexWriter for the index in path
.
Text will be analyzed with a
. If create
is true, then a new, empty index will be created in
path
, replacing the index already there, if any.
path
- the path to the index directorya
- the analyzer to usecreate
- true
to create the index or overwrite
the existing one; false
to append to the existing
index
IndexWriter
public IndexWriter(Directory d,
Analyzer a)
throws IOException
Constructs an IndexWriter for the index in
d
, creating it first if it does not
already exist, otherwise appending to the existing
index. Text will be analyzed with a
.
d
- the index directorya
- the analyzer to use
IndexWriter
public IndexWriter(Directory d,
Analyzer a,
boolean create)
throws 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.
d
- the index directorya
- the analyzer to usecreate
- true
to create the index or overwrite
the existing one; false
to append to the existing
index
addDocument
public void addDocument(Document doc)
throws 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 (every
setMaxBufferedDocs(int)
),
and also periodically merges segments in the index
(every
setMergeFactor(int)
flushes). When this
occurs, the method will take more time to run (possibly
a long time if the index is large), and will require
free temporary space in the Directory to do the
merging.
The amount of free space required when a merge is
triggered 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). Most
merges are small (merging the smallest segments
together), but whenever a full merge occurs (all
segments in the index, which is the worst case for
temporary space usage) then the maximum free disk space
required is the same as
optimize()
.
addDocument
public void addDocument(Document doc,
Analyzer analyzer)
throws 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.
addIndexes
public void addIndexes(IndexReader[] readers)
throws IOException
Merges the provided indexes into this index.
After this completes, the index is optimized.
The provided IndexReaders are not closed.
See
addIndexes(Directory[])
for
details on transactional semantics, temporary free
space required in the Directory, and non-CFS segments
on an Exception.
addIndexes
public void addIndexes(Directory[] dirs)
throws 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.
After this completes, the index is optimized.
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.
If an Exception is hit, it's still possible that all
indexes were successfully added. This happens when the
Exception is hit when trying to build a CFS file. In
this case, one segment in the index will be in non-CFS
format, even when using compound file format.
Also note that on an Exception, the index may still
have been partially or fully optimized even though none
of the input indexes were added.
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.
See
LUCENE-702
for details.
addIndexesNoOptimize
public void addIndexesNoOptimize(Directory[] dirs)
throws IOException
Merges all segments from an array of indexes into this index.
This is similar to addIndexes(Directory[]). However, no optimize()
is called either at the beginning or at the end. Instead, merges
are carried out as necessary.
This requires this index not be among those to be added, and the
upper bound* of those segment doc counts not exceed maxMergeDocs.
See
addIndexes(Directory[])
for
details on transactional semantics, temporary free
space required in the Directory, and non-CFS segments
on an Exception.
close
public void close()
throws IOException
Flushes all changes to an index and closes all
associated files.
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 (IndexReader.isLocked(directory)) {
IndexReader.unlock(directory);
}
}
after which, you must be certain not to use the writer
instance anymore.
deleteDocuments
public void deleteDocuments(Term term)
throws IOException
Deletes the document(s) containing term
.
term
- the term to identify the documents to be deleted
deleteDocuments
public void deleteDocuments(Term[] terms)
throws IOException
Deletes the document(s) containing any of the
terms. All deletes are flushed at the same time.
terms
- array of terms to identify the documents
to be deleted
docCount
public int docCount()
Returns the number of documents currently in this index.
finalize
protected void finalize()
throws Throwable
Release the write lock, if needed.
flush
public final void flush()
throws IOException
Flush all in-memory buffered updates (adds and deletes)
to the Directory.
getAnalyzer
public Analyzer getAnalyzer()
Returns the analyzer used by this index.
getDefaultWriteLockTimeout
public static long getDefaultWriteLockTimeout()
getDirectory
public Directory getDirectory()
Returns the Directory used by this index.
getInfoStream
public PrintStream getInfoStream()
getMaxBufferedDeleteTerms
public int getMaxBufferedDeleteTerms()
getMaxBufferedDocs
public int getMaxBufferedDocs()
getMaxFieldLength
public int getMaxFieldLength()
getMaxMergeDocs
public int getMaxMergeDocs()
getMergeFactor
public int getMergeFactor()
getSimilarity
public Similarity getSimilarity()
Expert: Return the Similarity implementation used by this IndexWriter.
This defaults to the current value of
Similarity.getDefault()
.
getTermIndexInterval
public int getTermIndexInterval()
Expert: Return the interval between indexed terms.
getUseCompoundFile
public boolean getUseCompoundFile()
Get the current setting of whether to use the compound file format.
Note that this just returns the value you set with setUseCompoundFile(boolean)
or the default. You cannot use this to query the status of an existing index.
getWriteLockTimeout
public long getWriteLockTimeout()
maybeFlushRamSegments
protected final void maybeFlushRamSegments()
throws IOException
numRamDocs
public final int numRamDocs()
Expert: Return the number of documents whose segments are currently cached in memory.
Useful when calling flushRamSegments()
optimize
public void optimize()
throws IOException
Merges all segments together into a single segment,
optimizing an index for search.
Note that this requires substantial temporary free
space in the Directory (see
LUCENE-764
for details):
-
If no readers/searchers are open against the index,
then free space required is up to 1X the total size of
the starting index. For example, if the starting
index is 10 GB, then you must have up to 10 GB of free
space before calling optimize.
-
If readers/searchers are using the index, then free
space required is up to 2X the size of the starting
index. This is because in addition to the 1X used by
optimize, the original 1X of the starting index is
still consuming space in the Directory as the readers
are holding the segments files open. Even on Unix,
where it will appear as if the files are gone ("ls"
won't list them), they still consume storage due to
"delete on last close" semantics.
Furthermore, if some but not all readers re-open
while the 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).
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.
ramSizeInBytes
public final long ramSizeInBytes()
Expert: Return the total size of all index files currently cached in memory.
Useful for size management with flushRamDocs()
setDefaultWriteLockTimeout
public static void setDefaultWriteLockTimeout(long writeLockTimeout)
Sets the default (for any instance of IndexWriter) maximum time to wait for a write lock (in
milliseconds).
setInfoStream
public void setInfoStream(PrintStream infoStream)
If non-null, information about merges and a message when
maxFieldLength is reached will be printed to this.
setMaxBufferedDeleteTerms
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.
The default value is
DEFAULT_MAX_BUFFERED_DELETE_TERMS
.
setMaxBufferedDocs
public void setMaxBufferedDocs(int maxBufferedDocs)
Determines the minimal number of documents required before the buffered
in-memory documents are merged and a new Segment is created.
Since Documents are merged in a
RAMDirectory
,
large value gives faster indexing. At the same time, mergeFactor limits
the number of files open in a FSDirectory.
The default value is 10.
setMaxFieldLength
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.
Note that this effectively truncates large documents, excluding from the
index 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 10,000 terms will be indexed for a field.
setMaxMergeDocs
public void setMaxMergeDocs(int maxMergeDocs)
Determines the largest number of documents ever merged by addDocument().
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
.
setMergeFactor
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 (<3210) for indices that are
interactively maintained.
This must never be less than 2. The default value is 10.
setSimilarity
public void setSimilarity(Similarity similarity)
Expert: Set the Similarity implementation used by this IndexWriter.
setTermIndexInterval
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.
setUseCompoundFile
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 once the segment creation
is finished. This is done regardless of what directory is in use.
setWriteLockTimeout
public void setWriteLockTimeout(long writeLockTimeout)
Sets the maximum time to wait for a write lock (in milliseconds) for this instance of IndexWriter. @see
updateDocument
public void updateDocument(Term term,
Document doc)
throws 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).
term
- the term to identify the document(s) to be
deleteddoc
- the document to be added
updateDocument
public void updateDocument(Term term,
Document doc,
Analyzer analyzer)
throws 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).
term
- the term to identify the document(s) to be
deleteddoc
- the document to be addedanalyzer
- the analyzer to use when analyzing the document