Package org.apache.lucene.util.fst

Class Builder<T>

  • public class Builder<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.

    • Constructor Detail

      • Builder

        public Builder​(FST.INPUT_TYPE inputType,
               int minSuffixCount1,
               int minSuffixCount2,
               boolean doShareSuffix,
               boolean doShareNonSingletonNodes,
               int shareMaxTailLength,
               Outputs<T> outputs,
               Builder.FreezeTail<T> freezeTail,
               boolean doPackFST,
               float acceptableOverheadRatio,
               boolean allowArrayArcs,
               int bytesPageBits)
        Instantiates an FST/FSA builder with all the possible tuning and construction tweaks. Read parameter documentation carefully.
        Parameters:
        inputType - The input type (transition labels). Can be anything from FST.INPUT_TYPE enumeration. Shorter types will consume less memory. Strings (character sequences) are represented as FST.INPUT_TYPE.BYTE4 (full unicode codepoints).
        minSuffixCount1 - If pruning the input graph during construction, this threshold is used for telling if a node is kept or pruned. If transition_count(node) >= minSuffixCount1, the node is kept.
        minSuffixCount2 - (Note: only Mike McCandless knows what this one is really doing...)
        doShareSuffix - If true, the shared suffixes will be compacted into unique paths. This requires an additional RAM-intensive hash map for lookups in memory. Setting this parameter to false creates a single suffix path for all input sequences. This will result in a larger FST, but requires substantially less memory and CPU during building.
        doShareNonSingletonNodes - Only used if doShareSuffix is true. Set this to true to ensure FST is fully minimal, at cost of more CPU and more RAM during building.
        shareMaxTailLength - Only used if doShareSuffix is true. Set this to Integer.MAX_VALUE to ensure FST is fully minimal, at cost of more CPU and more RAM during building.
        outputs - The output type for each input sequence. Applies only if building an FST. For FSA, use NoOutputs.getSingleton() and NoOutputs.getNoOutput() as the singleton output object.
        doPackFST - Pass true to create a packed FST.
        acceptableOverheadRatio - How to trade speed for space when building the FST. This option is only relevant when doPackFST is true. @see PackedInts#getMutable(int, int, float)
        allowArrayArcs - Pass false to disable the array arc optimization while building the FST; this will make the resulting FST smaller but slower to traverse.
        bytesPageBits - How many bits wide to make each byte[] block in the BytesStore; if you know the FST will be large then make this larger. For example 15 bits = 32768 byte pages.

    • Method Detail

      • getTotStateCount

        public long getTotStateCount()

      • getTermCount

        public long getTermCount()

      • getMappedStateCount

        public long getMappedStateCount()

      • add

        public void add​(IntsRef input,
                T output)
         throws IOException
        It's OK to add the same input twice in a row with different outputs, as long as outputs impls the merge 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

      • finish

        public FST<T> finish()
              throws IOException
        Returns final FST. NOTE: this will return null if nothing is accepted by the FST.
        Throws:
        IOException

      • fstSizeInBytes

        public long fstSizeInBytes()