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.

  • Method Details

    • 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()