Package org.apache.lucene.util.fst

Class FSTCompiler<T>

java.lang.Object

org.apache.lucene.util.fst.FSTCompiler<T>

public class FSTCompiler<T>
extends Object

Builds a minimal FST (maps an IntsRef term to an arbitrary output) from pre-sorted terms with outputs. The FST becomes an FSA if you use NoOutputs. The FST is written on-the-fly into a compact serialized format byte array, which can be saved to / loaded from a Directory or used directly for traversal. The FST is always finite (no cycles).

NOTE: The algorithm is described at http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.24.3698

The parameterized type T is the output type. See the subclasses of Outputs.

FSTs larger than 2.1GB are now possible (as of Lucene 4.2). FSTs containing more than 2.1B nodes are also now possible, however they cannot be packed.

It now supports 3 different workflows:

- Build FST and use it immediately entirely in RAM and then discard it

- Build FST and use it immediately entirely in RAM and also save it to other DataOutput, and load it later and use it

- Build FST but stream it immediately to disk (except the FSTMetaData, to be saved at the end). In order to use it, you need to construct the corresponding DataInput and use the FST constructor to read it.

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

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	FSTCompiler.Builder<T>	Fluent-style constructor for FST FSTCompiler.

Method Summary

Modifier and Type	Method	Description
void	add(IntsRef input, T output)	Add the next input/output pair.
FST.FSTMetadata<T>	compile()	Returns the metadata of the final FST.
long	fstRamBytesUsed()
long	fstSizeInBytes()
long	getArcCount()
float	getDirectAddressingMaxOversizingFactor()
FSTReader	getFSTReader()	Get the respective FSTReader of the DataOutput.
long	getNodeCount()
static DataOutput	getOnHeapReaderWriter(int blockBits)	Get an on-heap DataOutput that allows the FST to be read immediately after writing, and also optionally saved to an external DataOutput.

Methods inherited from class java.lang.Object

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

Method Detail

getOnHeapReaderWriter

public static DataOutput getOnHeapReaderWriter(int blockBits)

Get an on-heap DataOutput that allows the FST to be read immediately after writing, and also optionally saved to an external DataOutput.

Parameters:

blockBits - how many bits wide to make each block of the DataOutput

Returns:

the DataOutput

getFSTReader

public FSTReader getFSTReader()

Get the respective FSTReader of the DataOutput. To call this method, you need to use the default DataOutput or getOnHeapReaderWriter(int), otherwise we will throw an exception.

Returns:

the DataOutput as FSTReader

Throws:

IllegalStateException - if the DataOutput does not implement FSTReader

getDirectAddressingMaxOversizingFactor

public float getDirectAddressingMaxOversizingFactor()

getNodeCount

public long getNodeCount()

getArcCount

public long getArcCount()

add

public void add(IntsRef input,
                T output)
         throws IOException

Add the next input/output pair. The provided input must be sorted after the previous one according to IntsRef.compareTo(org.apache.lucene.util.IntsRef). It's also OK to add the same input twice in a row with different outputs, as long as Outputs implements the Outputs.merge(T, T) method. Note that input is fully consumed after this method is returned (so caller is free to reuse), but output is not. So if your outputs are changeable (eg ByteSequenceOutputs or IntSequenceOutputs) then you cannot reuse across calls.

Throws:

IOException

compile

public FST.FSTMetadata<T> compile()
                           throws IOException

Returns the metadata of the final FST. NOTE: this will return null if nothing is accepted by the FST themselves.

To create the FST, you need to:

- If a FSTReader DataOutput was used, such as the one returned by getOnHeapReaderWriter(int)

     fstMetadata = fstCompiler.compile();
     fst = FST.fromFSTReader(fstMetadata, fstCompiler.getFSTReader());
 

- If a non-FSTReader DataOutput was used, such as IndexOutput, you need to first create the corresponding DataInput, such as IndexInput then pass it to the FST construct

     fstMetadata = fstCompiler.compile();
     fst = new FST<>(fstMetadata, dataInput, new OffHeapFSTStore());
 

Throws:

IOException

fstRamBytesUsed

public long fstRamBytesUsed()

fstSizeInBytes

public long fstSizeInBytes()