Package org.apache.lucene.codecs.uniformsplit

Class FSTDictionary

java.lang.Object

org.apache.lucene.codecs.uniformsplit.FSTDictionary

All Implemented Interfaces:

IndexDictionary, Accountable

public class FSTDictionary
extends Object
implements IndexDictionary

Immutable stateless FST-based index dictionary kept in memory.

Use IndexDictionary.Builder to build the IndexDictionary.

Create a stateful IndexDictionary.Browser to seek a term in this IndexDictionary and get its corresponding block file pointer to the terms block file.

Its greatest advantage is to be very compact in memory thanks to both the compaction of the FST as a byte array, and the incremental encoding of the leaves block pointer values, which are long integers in increasing order, with PositiveIntOutputs.
With a compact dictionary in memory we can increase the number of blocks. This allows us to reduce the average block size, which means faster scan inside a block.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
protected class	FSTDictionary.Browser	Stateful FSTDictionary.Browser to seek a term in this FSTDictionary and get its corresponding block file pointer in the block file.
static class	FSTDictionary.BrowserSupplier	Provides stateful FSTDictionary.Browser to seek in the FSTDictionary.
static class	FSTDictionary.Builder	Builds an immutable FSTDictionary.

Field Summary

Fields

Modifier and Type	Field	Description
private static final long	BASE_RAM_USAGE
protected final FST<Long>	fst

Fields inherited from interface org.apache.lucene.util.Accountable

NULL_ACCOUNTABLE

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	FSTDictionary(FST<Long> fst)

Method Summary

Modifier and Type	Method	Description
FSTDictionary.Browser	browser()	Creates a new IndexDictionary.Browser.
long	ramBytesUsed()	Return the memory usage of this object in bytes.
protected static FSTDictionary	read(DataInput input, BlockDecoder blockDecoder, boolean isFSTOnHeap)	Reads a FSTDictionary from the provided input.
void	write(DataOutput output, BlockEncoder blockEncoder)	Writes this dictionary to the provided output.

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.lucene.util.Accountable

getChildResources

Field Details

BASE_RAM_USAGE

private static final long BASE_RAM_USAGE

fst

protected final FST<Long> fst

Constructor Details

FSTDictionary

protected FSTDictionary(FST<Long> fst)

Method Details

ramBytesUsed

public long ramBytesUsed()

Description copied from interface: Accountable

Return the memory usage of this object in bytes. Negative values are illegal.

Specified by:

ramBytesUsed in interface Accountable

write

public void write(DataOutput output,
 BlockEncoder blockEncoder)
           throws IOException

Description copied from interface: IndexDictionary

Writes this dictionary to the provided output.

Specified by:

write in interface IndexDictionary

Parameters:

blockEncoder - The BlockEncoder for specific encoding of this index dictionary; or null if none.

Throws:

IOException

read

protected static FSTDictionary read(DataInput input,
 BlockDecoder blockDecoder,
 boolean isFSTOnHeap)
                             throws IOException

Reads a FSTDictionary from the provided input.

Parameters:

blockDecoder - The BlockDecoder to use for specific decoding; or null if none.

Throws:

IOException

browser

public FSTDictionary.Browser browser()

Description copied from interface: IndexDictionary

Creates a new IndexDictionary.Browser.

Specified by:

browser in interface IndexDictionary