Package org.apache.lucene.util.fst

Class Builder<T>

  • public class Builder<T>
extends java.lang.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.

    • Field Detail

      • DIRECT_ADDRESSING_MAX_OVERSIZING_FACTOR

        static final float DIRECT_ADDRESSING_MAX_OVERSIZING_FACTOR
        Default oversizing factor used to decide whether to encode a node with direct addressing or binary search. Default is 1: ensure no oversizing on average.

        This factor does not determine whether to encode a node with a list of variable length arcs or with fixed length arcs. It only determines the effective encoding of a node that is already known to be encoded with fixed length arcs. See FST.shouldExpandNodeWithFixedLengthArcs() and FST.shouldExpandNodeWithDirectAddressing().

        For English words we measured 217K nodes, only 3.27% nodes are encoded with fixed length arcs, and 99.99% of them with direct addressing. Overall FST memory reduced by 1.67%.

        For worst case we measured 168K nodes, 50% of them are encoded with fixed length arcs, and 14% of them with direct encoding. Overall FST memory reduced by 0.8%.

        Use TestFstDirectAddressing.main() and TestFstDirectAddressing.testWorstCaseForDirectAddressing() to evaluate a change.

        See Also:
        setDirectAddressingMaxOversizingFactor(float), Constant Field Values

      • dedupHash

        private final NodeHash<T> dedupHash

      • fst

        final FST<T> fst

      • NO_OUTPUT

        private final T NO_OUTPUT

      • minSuffixCount1

        private final int minSuffixCount1

      • minSuffixCount2

        private final int minSuffixCount2

      • doShareNonSingletonNodes

        private final boolean doShareNonSingletonNodes

      • shareMaxTailLength

        private final int shareMaxTailLength

      • lastFrozenNode

        long lastFrozenNode

      • numBytesPerArc

        int[] numBytesPerArc

      • numLabelBytesPerArc

        int[] numLabelBytesPerArc

      • arcCount

        long arcCount

      • nodeCount

        long nodeCount

      • binarySearchNodeCount

        long binarySearchNodeCount

      • directAddressingNodeCount

        long directAddressingNodeCount

      • allowFixedLengthArcs

        boolean allowFixedLengthArcs

      • directAddressingMaxOversizingFactor

        float directAddressingMaxOversizingFactor

      • directAddressingExpansionCredit

        long directAddressingExpansionCredit

    • Constructor Detail

      • Builder

        public Builder​(FST.INPUT_TYPE inputType,
               int minSuffixCount1,
               int minSuffixCount2,
               boolean doShareSuffix,
               boolean doShareNonSingletonNodes,
               int shareMaxTailLength,
               Outputs<T> outputs,
               boolean allowFixedLengthArcs,
               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.
        allowFixedLengthArcs - Pass false to disable the fixed length arc optimization (binary search or direct addressing) 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

      • setDirectAddressingMaxOversizingFactor

        public Builder<T> setDirectAddressingMaxOversizingFactor​(float factor)
        Overrides the default the maximum oversizing of fixed array allowed to enable direct addressing of arcs instead of binary search.

        Setting this factor to a negative value (e.g. -1) effectively disables direct addressing, only binary search nodes will be created.

        See Also:
        DIRECT_ADDRESSING_MAX_OVERSIZING_FACTOR

      • getTermCount

        public long getTermCount()

      • getNodeCount

        public long getNodeCount()

      • getArcCount

        public long getArcCount()

      • getMappedStateCount

        public long getMappedStateCount()

      • freezeTail

        private void freezeTail​(int prefixLenPlus1)
                 throws java.io.IOException
        Throws:
        java.io.IOException

      • add

        public void add​(IntsRef input,
                T output)
         throws java.io.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:
        java.io.IOException

      • validOutput

        private boolean validOutput​(T output)

      • finish

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

      • compileAllTargets

        private void compileAllTargets​(Builder.UnCompiledNode<T> node,
                               int tailLength)
                        throws java.io.IOException
        Throws:
        java.io.IOException

      • fstRamBytesUsed

        public long fstRamBytesUsed()