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## org.apache.lucene.index
Class ParallelReader

    java.lang.Object
      org.apache.lucene.index.IndexReader
          org.apache.lucene.index.ParallelReader

    public class ParallelReader

extends IndexReader

An IndexReader which reads multiple, parallel indexes. Each index added must have the same number of documents, but typically each contains different fields. Each document contains the union of the fields of all documents with the same document number. When searching, matches for a query term are from the first index added that has the field.

This is useful, e.g., with collections that have large fields which change rarely and small fields that change more frequently. The smaller fields may be re-indexed in a new index and both indexes may be searched together.

Warning: It is up to you to make sure all indexes are created and modified the same way. For example, if you add documents to one index, you need to add the same documents in the same order to the other indexes. Failure to do so will result in undefined behavior.

Nested Class Summary

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

Field Summary

Fields inherited from class org.apache.lucene.index.IndexReader
`hasChanges`

Constructor Summary
`ParallelReader()` Construct a ParallelReader.
`ParallelReader(boolean closeSubReaders)` Construct a ParallelReader.

Method Summary
`void` | `add(IndexReader reader)` Add an IndexReader.
`void` | `add(IndexReader reader, boolean ignoreStoredFields)` Add an IndexReader whose stored fields will not be returned.
`int` | `docFreq(Term term)` Returns the number of documents containing the term `t`.
`protected void` | `doClose()` Implements close.
`protected void` | `doCommit()` Implements commit.
`Document` | `document(int n, FieldSelector fieldSelector)` Get the `Document` at the `n`th position.
`protected void` | `doDelete(int n)` Implements deletion of the document numbered `docNum`.
`protected void` | `doSetNorm(int n, String field, byte value)` Implements setNorm in subclass.
`protected void` | `doUndeleteAll()` Implements actual undeleteAll() in subclass.
`Collection` | `getFieldNames(IndexReader.FieldOption fieldNames)` Get a list of unique field names that exist in this index and have the specified field option information.
`TermFreqVector` | `getTermFreqVector(int n, String field)` Return a term frequency vector for the specified document and field.
`void` | `getTermFreqVector(int docNumber, String field, TermVectorMapper mapper)` Load the Term Vector into a user-defined data structure instead of relying on the parallel arrays of the `TermFreqVector`.
`void` | `getTermFreqVector(int docNumber, TermVectorMapper mapper)` Map all the term vectors for all fields in a Document
`TermFreqVector[]` | `getTermFreqVectors(int n)` Return an array of term frequency vectors for the specified document.
`long` | `getVersion()` Not implemented.
`boolean` | `hasDeletions()` Returns true if any documents have been deleted
`boolean` | `hasNorms(String field)` Returns true if there are norms stored for this field.
`boolean` | `isCurrent()` Checks recursively if all subreaders are up to date.
`boolean` | `isDeleted(int n)` Returns true if document n has been deleted
`boolean` | `isOptimized()` Checks recursively if all subindexes are optimized
`int` | `maxDoc()` Returns one greater than the largest possible document number.
`byte[]` | `norms(String field)` Returns the byte-encoded normalization factor for the named field of every document.
`void` | `norms(String field, byte[] result, int offset)` Reads the byte-encoded normalization factor for the named field of every document.
`int` | `numDocs()` Returns the number of documents in this index.
`IndexReader` | `reopen()` Tries to reopen the subreaders.
`TermDocs` | `termDocs()` Returns an unpositioned `TermDocs` enumerator.
`TermDocs` | `termDocs(Term term)` Returns an enumeration of all the documents which contain `term`.
`TermPositions` | `termPositions()` Returns an unpositioned `TermPositions` enumerator.
`TermPositions` | `termPositions(Term term)` Returns an enumeration of all the documents which contain `term`.
`TermEnum` | `terms()` Returns an enumeration of all the terms in the index.
`TermEnum` | `terms(Term term)` Returns an enumeration of all terms starting at a given term.

Methods inherited from class org.apache.lucene.index.IndexReader
`acquireWriteLock, close, commit, decRef, deleteDocument, deleteDocuments, directory, document, ensureOpen, flush, getCurrentVersion, getCurrentVersion, getCurrentVersion, getTermInfosIndexDivisor, incRef, indexExists, indexExists, indexExists, isLocked, isLocked, lastModified, lastModified, lastModified, main, open, open, open, open, setNorm, setNorm, setTermInfosIndexDivisor, undeleteAll, unlock`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### ParallelReader

    public ParallelReader()
                   throws IOException

  Construct a ParallelReader.

  Note that all subreaders are closed if this ParallelReader is closed.

  Throws:
    `IOException`

### ParallelReader

    public ParallelReader(boolean closeSubReaders)
                   throws IOException

  Construct a ParallelReader.

  Parameters:
    `closeSubReaders` - indicates whether the subreaders should be closed when this ParallelReader is closed
  Throws:
    `IOException`

Method Detail

### add

    public void add(IndexReader reader)
             throws IOException

  Add an IndexReader.

  Throws:
    `IOException` - if there is a low-level IO error

### add

    public void add(IndexReader reader,
                    boolean ignoreStoredFields)
             throws IOException

  Add an IndexReader whose stored fields will not be returned. This can accellerate search when stored fields are only needed from a subset of the IndexReaders.

  Throws:
    `IllegalArgumentException` - if not all indexes contain the same number of documents
    `IllegalArgumentException` - if not all indexes have the same value of `IndexReader.maxDoc()`
    `IOException` - if there is a low-level IO error

### reopen

    public IndexReader reopen()
                       throws CorruptIndexException,
                              IOException

  Tries to reopen the subreaders.
  If one or more subreaders could be re-opened (i. e. subReader.reopen() returned a new instance != subReader), then a new ParallelReader instance is returned, otherwise this instance is returned.

  A re-opened instance might share one or more subreaders with the old instance. Index modification operations result in undefined behavior when performed before the old instance is closed. (see `IndexReader.reopen()`).

  If subreaders are shared, then the reference count of those readers is increased to ensure that the subreaders remain open until the last referring reader is closed.

  Overrides:
    `reopen` in class `IndexReader`
  Throws:
    `CorruptIndexException` - if the index is corrupt
    `IOException` - if there is a low-level IO error

### numDocs

    public int numDocs()

  Description copied from class: `IndexReader`
  Returns the number of documents in this index.

  Specified by:
    `numDocs` in class `IndexReader`

### maxDoc

    public int maxDoc()

  Description copied from class: `IndexReader`
  Returns one greater than the largest possible document number. This may be used to, e.g., determine how big to allocate an array which will have an element for every document number in an index.

  Specified by:
    `maxDoc` in class `IndexReader`

### hasDeletions

    public boolean hasDeletions()

  Description copied from class: `IndexReader`
  Returns true if any documents have been deleted

  Specified by:
    `hasDeletions` in class `IndexReader`

### isDeleted

    public boolean isDeleted(int n)

  Description copied from class: `IndexReader`
  Returns true if document n has been deleted

  Specified by:
    `isDeleted` in class `IndexReader`

### doDelete

    protected void doDelete(int n)
                     throws CorruptIndexException,
                            IOException

  Description copied from class: `IndexReader`
  Implements deletion of the document numbered `docNum`. Applications should call `IndexReader.deleteDocument(int)` or `IndexReader.deleteDocuments(Term)`.

  Specified by:
    `doDelete` in class `IndexReader`
  Throws:
    `CorruptIndexException`
    `IOException`

### doUndeleteAll

    protected void doUndeleteAll()
                          throws CorruptIndexException,
                                 IOException

  Description copied from class: `IndexReader`
  Implements actual undeleteAll() in subclass.

  Specified by:
    `doUndeleteAll` in class `IndexReader`
  Throws:
    `CorruptIndexException`
    `IOException`

### document

    public Document document(int n,
                             FieldSelector fieldSelector)
                      throws CorruptIndexException,
                             IOException

  Description copied from class: `IndexReader`
  Get the `Document` at the `n`th position. The `FieldSelector` may be used to determine what `Field`s to load and how they should be loaded. NOTE: If this Reader (more specifically, the underlying `FieldsReader`) is closed before the lazy `Field` is loaded an exception may be thrown. If you want the value of a lazy `Field` to be available after closing you must explicitly load it or fetch the Document again with a new loader.

  Specified by:
    `document` in class `IndexReader`
  Parameters:
    `n` - Get the document at the `n`th position
    `fieldSelector` - The `FieldSelector` to use to determine what Fields should be loaded on the Document. May be null, in which case all Fields will be loaded.
  Returns:
    The stored fields of the `Document` at the nth position
  Throws:
    `CorruptIndexException` - if the index is corrupt
    `IOException` - if there is a low-level IO error
  See Also:
    `Fieldable`, `FieldSelector`, `SetBasedFieldSelector`, `LoadFirstFieldSelector`

### getTermFreqVectors

    public TermFreqVector[] getTermFreqVectors(int n)
                                        throws IOException

  Description copied from class: `IndexReader`
  Return an array of term frequency vectors for the specified document. The array contains a vector for each vectorized field in the document. Each vector contains terms and frequencies for all terms in a given vectorized field. If no such fields existed, the method returns null. The term vectors that are returned my either be of type TermFreqVector or of type TermPositionsVector if positions or offsets have been stored.

  Specified by:
    `getTermFreqVectors` in class `IndexReader`
  Parameters:
    `n` - document for which term frequency vectors are returned
  Returns:
    array of term frequency vectors. May be null if no term vectors have been stored for the specified document.
  Throws:
    `IOException` - if index cannot be accessed
  See Also:
    `Field.TermVector`

### getTermFreqVector

    public TermFreqVector getTermFreqVector(int n,
                                            String field)
                                     throws IOException

  Description copied from class: `IndexReader`
  Return a term frequency vector for the specified document and field. The returned vector contains terms and frequencies for the terms in the specified field of this document, if the field had the storeTermVector flag set. If termvectors had been stored with positions or offsets, a TermPositionsVector is returned.

  Specified by:
    `getTermFreqVector` in class `IndexReader`
  Parameters:
    `n` - document for which the term frequency vector is returned
    `field` - field for which the term frequency vector is returned.
  Returns:
    term frequency vector May be null if field does not exist in the specified document or term vector was not stored.
  Throws:
    `IOException` - if index cannot be accessed
  See Also:
    `Field.TermVector`

### getTermFreqVector

    public void getTermFreqVector(int docNumber,
                                  String field,
                                  TermVectorMapper mapper)
                           throws IOException

  Description copied from class: `IndexReader`
  Load the Term Vector into a user-defined data structure instead of relying on the parallel arrays of the `TermFreqVector`.

  Specified by:
    `getTermFreqVector` in class `IndexReader`
  Parameters:
    `docNumber` - The number of the document to load the vector for
    `field` - The name of the field to load
    `mapper` - The `TermVectorMapper` to process the vector. Must not be null
  Throws:
    `IOException` - if term vectors cannot be accessed or if they do not exist on the field and doc. specified.

### getTermFreqVector

    public void getTermFreqVector(int docNumber,
                                  TermVectorMapper mapper)
                           throws IOException

  Description copied from class: `IndexReader`
  Map all the term vectors for all fields in a Document

  Specified by:
    `getTermFreqVector` in class `IndexReader`
  Parameters:
    `docNumber` - The number of the document to load the vector for
    `mapper` - The `TermVectorMapper` to process the vector. Must not be null
  Throws:
    `IOException` - if term vectors cannot be accessed or if they do not exist on the field and doc. specified.

### hasNorms

    public boolean hasNorms(String field)
                     throws IOException

  Description copied from class: `IndexReader`
  Returns true if there are norms stored for this field.

  Overrides:
    `hasNorms` in class `IndexReader`
  Throws:
    `IOException`

### norms

    public byte[] norms(String field)
                 throws IOException

  Description copied from class: `IndexReader`
  Returns the byte-encoded normalization factor for the named field of every document. This is used by the search code to score documents.

  Specified by:
    `norms` in class `IndexReader`
  Throws:
    `IOException`
  See Also:
    `AbstractField.setBoost(float)`

### norms

    public void norms(String field,
                      byte[] result,
                      int offset)
               throws IOException

  Description copied from class: `IndexReader`
  Reads the byte-encoded normalization factor for the named field of every document. This is used by the search code to score documents.

  Specified by:
    `norms` in class `IndexReader`
  Throws:
    `IOException`
  See Also:
    `AbstractField.setBoost(float)`

### doSetNorm

    protected void doSetNorm(int n,
                             String field,
                             byte value)
                      throws CorruptIndexException,
                             IOException

  Description copied from class: `IndexReader`
  Implements setNorm in subclass.

  Specified by:
    `doSetNorm` in class `IndexReader`
  Throws:
    `CorruptIndexException`
    `IOException`

### terms

    public TermEnum terms()
                   throws IOException

  Description copied from class: `IndexReader`
  Returns an enumeration of all the terms in the index. The enumeration is ordered by Term.compareTo(). Each term is greater than all that precede it in the enumeration. Note that after calling terms(), `TermEnum.next()` must be called on the resulting enumeration before calling other methods such as `TermEnum.term()`.

  Specified by:
    `terms` in class `IndexReader`
  Throws:
    `IOException` - if there is a low-level IO error

### terms

    public TermEnum terms(Term term)
                   throws IOException

  Description copied from class: `IndexReader`
  Returns an enumeration of all terms starting at a given term. If the given term does not exist, the enumeration is positioned at the first term greater than the supplied therm. The enumeration is ordered by Term.compareTo(). Each term is greater than all that precede it in the enumeration.

  Specified by:
    `terms` in class `IndexReader`
  Throws:
    `IOException` - if there is a low-level IO error

### docFreq

    public int docFreq(Term term)
                throws IOException

  Description copied from class: `IndexReader`
  Returns the number of documents containing the term `t`.

  Specified by:
    `docFreq` in class `IndexReader`
  Throws:
    `IOException` - if there is a low-level IO error

### termDocs

    public TermDocs termDocs(Term term)
                      throws IOException

  Description copied from class: `IndexReader`
  Returns an enumeration of all the documents which contain `term`. For each document, the document number, the frequency of the term in that document is also provided, for use in search scoring. Thus, this method implements the mapping:

  Term => <docNum, freq>*

  The enumeration is ordered by document number. Each document number is greater than all that precede it in the enumeration.

  Overrides:
    `termDocs` in class `IndexReader`
  Throws:
    `IOException` - if there is a low-level IO error

### termDocs

    public TermDocs termDocs()
                      throws IOException

  Description copied from class: `IndexReader`
  Returns an unpositioned `TermDocs` enumerator.

  Specified by:
    `termDocs` in class `IndexReader`
  Throws:
    `IOException` - if there is a low-level IO error

### termPositions

    public TermPositions termPositions(Term term)
                                throws IOException

  Description copied from class: `IndexReader`
  Returns an enumeration of all the documents which contain `term`. For each document, in addition to the document number and frequency of the term in that document, a list of all of the ordinal positions of the term in the document is available. Thus, this method implements the mapping:

  Term => <docNum, freq, <pos1, pos2, ... posfreq-1> >*

  This positional information facilitates phrase and proximity searching.

  The enumeration is ordered by document number. Each document number is greater than all that precede it in the enumeration.

  Overrides:
    `termPositions` in class `IndexReader`
  Throws:
    `IOException` - if there is a low-level IO error

### termPositions

    public TermPositions termPositions()
                                throws IOException

  Description copied from class: `IndexReader`
  Returns an unpositioned `TermPositions` enumerator.

  Specified by:
    `termPositions` in class `IndexReader`
  Throws:
    `IOException` - if there is a low-level IO error

### isCurrent

    public boolean isCurrent()
                      throws CorruptIndexException,
                             IOException

  Checks recursively if all subreaders are up to date.

  Overrides:
    `isCurrent` in class `IndexReader`
  Throws:
    `CorruptIndexException` - if the index is corrupt
    `IOException` - if there is a low-level IO error

### isOptimized

    public boolean isOptimized()

  Checks recursively if all subindexes are optimized

  Overrides:
    `isOptimized` in class `IndexReader`
  Returns:
    `true` if the index is optimized; `false` otherwise

### getVersion

    public long getVersion()

  Not implemented.

  Overrides:
    `getVersion` in class `IndexReader`
  Throws:
    `UnsupportedOperationException`

### doCommit

    protected void doCommit()
                     throws IOException

  Description copied from class: `IndexReader`
  Implements commit.

  Specified by:
    `doCommit` in class `IndexReader`
  Throws:
    `IOException`

### doClose

    protected void doClose()
                    throws IOException

  Description copied from class: `IndexReader`
  Implements close.

  Specified by:
    `doClose` in class `IndexReader`
  Throws:
    `IOException`

### getFieldNames

    public Collection getFieldNames(IndexReader.FieldOption fieldNames)

  Description copied from class: `IndexReader`
  Get a list of unique field names that exist in this index and have the specified field option information.

  Specified by:
    `getFieldNames` in class `IndexReader`
  Parameters:
    `fieldNames` - specifies which field option should be available for the returned fields
  Returns:
    Collection of Strings indicating the names of the fields.
  See Also:
    `IndexReader.FieldOption`

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