Package org.apache.lucene.util.fst
Class Builder<T>
- java.lang.Object
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- org.apache.lucene.util.fst.Builder<T>
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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.
- WARNING: This API is experimental and might change in incompatible ways in the next release.
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Nested Class Summary
Nested Classes Modifier and Type Class Description static class
Builder.Arc<T>
Expert: holds a pending (seen but not yet serialized) arc.static class
Builder.UnCompiledNode<T>
Expert: holds a pending (seen but not yet serialized) Node.
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Constructor Summary
Constructors Constructor Description 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.Builder(FST.INPUT_TYPE inputType, Outputs<T> outputs)
Instantiates an FST/FSA builder without any pruning.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
add(IntsRef input, T output)
Add the next input/output pair.FST<T>
finish()
Returns final FST.long
fstRamBytesUsed()
long
getArcCount()
float
getDirectAddressingMaxOversizingFactor()
long
getMappedStateCount()
long
getNodeCount()
long
getTermCount()
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.
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Constructor Detail
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Builder
public Builder(FST.INPUT_TYPE inputType, Outputs<T> outputs)
Instantiates an FST/FSA builder without any pruning. A shortcut toBuilder(FST.INPUT_TYPE, int, int, boolean, boolean, int, Outputs, boolean, int)
with pruning options turned off.
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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 fromFST.INPUT_TYPE
enumeration. Shorter types will consume less memory. Strings (character sequences) are represented asFST.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
- Iftrue
, the shared suffixes will be compacted into unique paths. This requires an additional RAM-intensive hash map for lookups in memory. Setting this parameter tofalse
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, useNoOutputs.getSingleton()
andNoOutputs.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.
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Method Detail
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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
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getDirectAddressingMaxOversizingFactor
public float getDirectAddressingMaxOversizingFactor()
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getTermCount
public long getTermCount()
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getNodeCount
public long getNodeCount()
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getArcCount
public long getArcCount()
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getMappedStateCount
public long getMappedStateCount()
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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 toIntsRef.compareTo(org.apache.lucene.util.IntsRef)
. It's also OK to add the same input twice in a row with different outputs, as long asOutputs
implements theOutputs.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 (egByteSequenceOutputs
orIntSequenceOutputs
) then you cannot reuse across calls.- Throws:
IOException
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finish
public FST<T> finish() throws IOException
Returns final FST. NOTE: this will return null if nothing is accepted by the FST.- Throws:
IOException
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fstRamBytesUsed
public long fstRamBytesUsed()
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