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.
Get an on-heap DataOutput that allows the FST to be read immediately after writing, and also optionally saved to an external DataOutput.
| name | type | description |
|---|---|---|
| block_bits | int | how many bits wide to make each block of the DataOutput |
Returns: the DataOutput
Add the next input/output pair. The provided input must be sorted after the previous one
according to IntsRef#compareTo. It's also OK to add the same input twice in a row with
different outputs, as long as Outputs implements the Outputs#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.
getArcCount() · also: get_arc_countReturns 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 org.apache.lucene.store.IndexOutput, you need to first create the corresponding org.apache.lucene.store.DataInput, such as org.apache.lucene.store.IndexInput then
pass it to the FST construct
fstMetadata = fstCompiler.compile();
fst = new FST<>(fstMetadata, dataInput, new OffHeapFSTStore());
getDirectAddressingMaxOversizingFactor() · also: get_direct_addressing_max_oversizing_factorfstRamBytesUsed()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
| IllegalStateException | if the DataOutput does not implement FSTReader | |
fstSizeInBytes()getNodeCount() · also: get_node_count