Package org.apache.lucene.util

Class BytesRefHash

java.lang.Object

org.apache.lucene.util.BytesRefHash

public final class BytesRefHash
extends Object

BytesRefHash is a special purpose hash-map like data-structure optimized for BytesRef instances. BytesRefHash maintains mappings of byte arrays to ids (Map<BytesRef,int>) storing the hashed bytes efficiently in continuous storage. The mapping to the id is encapsulated inside BytesRefHash and is guaranteed to be increased for each added BytesRef.

Note: The maximum capacity BytesRef instance passed to add(BytesRef) must not be longer than ByteBlockPool.BYTE_BLOCK_SIZE-2. The internal storage is limited to 2GB total byte storage.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	BytesRefHash.BytesStartArray	Manages allocation of the per-term addresses.
static class	BytesRefHash.DirectBytesStartArray	A simple BytesRefHash.BytesStartArray that tracks memory allocation using a private Counter instance.
static class	BytesRefHash.MaxBytesLengthExceededException	Thrown if a BytesRef exceeds the BytesRefHash limit of ByteBlockPool.BYTE_BLOCK_SIZE-2.

Field Summary

Fields

Modifier and Type	Field	Description
static int	DEFAULT_CAPACITY

Constructor Summary

Constructors

Constructor	Description
BytesRefHash()	Creates a new BytesRefHash with a ByteBlockPool using a ByteBlockPool.DirectAllocator.
BytesRefHash(ByteBlockPool pool)	Creates a new BytesRefHash
BytesRefHash(ByteBlockPool pool, int capacity, BytesRefHash.BytesStartArray bytesStartArray)	Creates a new BytesRefHash

Method Summary

Modifier and Type	Method	Description
int	add(BytesRef bytes)	Adds a new BytesRef
int	add(BytesRef bytes, int code)	Adds a new BytesRef with a pre-calculated hash code.
int	addByPoolOffset(int offset)	Adds a "arbitrary" int offset instead of a BytesRef term.
int	byteStart(int bytesID)	Returns the bytesStart offset into the internally used ByteBlockPool for the given bytesID
void	clear()
void	clear(boolean resetPool)	Clears the BytesRef which maps to the given BytesRef
void	close()	Closes the BytesRefHash and releases all internally used memory
int	find(BytesRef bytes)	Returns the id of the given BytesRef.
int	find(BytesRef bytes, int code)	Returns the id of the given BytesRef with a pre-calculated hash code.
BytesRef	get(int bytesID, BytesRef ref)	Populates and returns a BytesRef with the bytes for the given bytesID.
void	reinit()	reinitializes the BytesRefHash after a previous clear() call.
int	size()	Returns the number of BytesRef values in this BytesRefHash.
int[]	sort(Comparator<BytesRef> comp)	Returns the values array sorted by the referenced byte values.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_CAPACITY

public static final int DEFAULT_CAPACITY

See Also:

Constant Field Values

Constructor Detail

BytesRefHash

public BytesRefHash()

Creates a new BytesRefHash with a ByteBlockPool using a ByteBlockPool.DirectAllocator.

BytesRefHash

public BytesRefHash(ByteBlockPool pool)

Creates a new BytesRefHash

BytesRefHash

public BytesRefHash(ByteBlockPool pool,
                    int capacity,
                    BytesRefHash.BytesStartArray bytesStartArray)

Creates a new BytesRefHash

Method Detail

size

public int size()

Returns the number of BytesRef values in this BytesRefHash.

Returns:

the number of BytesRef values in this BytesRefHash.

get

public BytesRef get(int bytesID,
                    BytesRef ref)

Populates and returns a BytesRef with the bytes for the given bytesID.

Note: the given bytesID must be a positive integer less than the current size (size())

Parameters:

bytesID - the id

ref - the BytesRef to populate

Returns:

the given BytesRef instance populated with the bytes for the given bytesID

sort

public int[] sort(Comparator<BytesRef> comp)

Returns the values array sorted by the referenced byte values.

Note: This is a destructive operation. clear() must be called in order to reuse this BytesRefHash instance.

Parameters:

comp - the Comparator used for sorting

clear

public void clear(boolean resetPool)

Clears the BytesRef which maps to the given BytesRef

clear

public void clear()

close

public void close()

Closes the BytesRefHash and releases all internally used memory

add

public int add(BytesRef bytes)

Adds a new BytesRef

Parameters:

bytes - the bytes to hash

Returns:

the id the given bytes are hashed if there was no mapping for the given bytes, otherwise (-(id)-1). This guarantees that the return value will always be >= 0 if the given bytes haven't been hashed before.

Throws:

BytesRefHash.MaxBytesLengthExceededException - if the given bytes are > 2 + ByteBlockPool.BYTE_BLOCK_SIZE

add

public int add(BytesRef bytes,
               int code)

Adds a new BytesRef with a pre-calculated hash code.

Parameters:

bytes - the bytes to hash

code - the bytes hash code

Hashcode is defined as:

 int hash = 0;
 for (int i = offset; i < offset + length; i++) {
   hash = 31 * hash + bytes[i];
 }
 

Returns:

the id the given bytes are hashed if there was no mapping for the given bytes, otherwise (-(id)-1). This guarantees that the return value will always be >= 0 if the given bytes haven't been hashed before.

Throws:

BytesRefHash.MaxBytesLengthExceededException - if the given bytes are > ByteBlockPool.BYTE_BLOCK_SIZE - 2

find

public int find(BytesRef bytes)

Returns the id of the given BytesRef.

See Also:

find(BytesRef, int)

find

public int find(BytesRef bytes,
                int code)

Returns the id of the given BytesRef with a pre-calculated hash code.

Parameters:

bytes - the bytes to look for

code - the bytes hash code

Returns:

the id of the given bytes, or -1 if there is no mapping for the given bytes.

addByPoolOffset

public int addByPoolOffset(int offset)

Adds a "arbitrary" int offset instead of a BytesRef term. This is used in the indexer to hold the hash for term vectors, because they do not redundantly store the byte[] term directly and instead reference the byte[] term already stored by the postings BytesRefHash. See add(int textStart) in TermsHashPerField.

reinit

public void reinit()

reinitializes the BytesRefHash after a previous clear() call. If clear() has not been called previously this method has no effect.

byteStart

public int byteStart(int bytesID)

Returns the bytesStart offset into the internally used ByteBlockPool for the given bytesID

Parameters:

bytesID - the id to look up

Returns:

the bytesStart offset into the internally used ByteBlockPool for the given id