Lucene94FieldInfosFormat

Lucene 9.0 Field Infos format.

Field names are stored in the field info file, with suffix .fnm.

FieldInfos (.fnm) --> Header,FieldsCount, ^FieldsCount,Footer

Data types:

• Header -->IndexHeader

• FieldsCount -->DataOutput.writeVInt

• FieldName -->DataOutput.writeString

• FieldBits, IndexOptions, DocValuesBits -->DataOutput.writeByte

• FieldNumber, DimensionCount, DimensionNumBytes -->DataOutput.writeInt

• Attributes -->DataOutput.writeMapOfStrings

• DocValuesGen -->DataOutput.writeLong

• Footer -->CodecFooter

Field Descriptions:

• FieldsCount: the number of fields in this file.

• FieldName: name of the field as a UTF-8 String.

• FieldNumber: the field's number. Note that unlike previous versions of Lucene, the fields are not numbered implicitly by their order in the file, instead explicitly.

• FieldBits: a byte containing field options.

• The low order bit (0x1) is one for fields that have term vectors stored, and zero for fields without term vectors.

• If the second lowest order-bit is set (0x2), norms are omitted for the indexed field.

• If the third lowest-order bit is set (0x4), payloads are stored for the indexed field.

• IndexOptions: a byte containing index options.

• 0: not indexed

• 1: indexed as DOCS_ONLY

• 2: indexed as DOCS_AND_FREQS

• 3: indexed as DOCS_AND_FREQS_AND_POSITIONS

• 4: indexed as DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS

• DocValuesBits: a byte containing per-document value types. The type recorded as two four-bit integers, with the high-order bits representing norms options, and the low-order bits representing DocValues options. Each four-bit integer can be decoded as such:

• 0: no DocValues for this field.

• 1: NumericDocValues. (DocValuesType.NUMERIC)

• 2: BinaryDocValues. (DocValuesType#BINARY)

• 3: SortedDocValues. (DocValuesType#SORTED)

• DocValuesGen is the generation count of the field's DocValues. If this is -1, there are no DocValues updates to that field. Anything above zero means there are updates stored by DocValuesFormat.

• Attributes: a key-value map of codec-private attributes.

• PointDimensionCount, PointNumBytes: these are non-zero only if the field is indexed as points, e.g. using org.gnit.lucenekmp.document.LongPoint

• VectorDimension: it is non-zero if the field is indexed as vectors.

• VectorEncoding: a byte containing the encoding of vector values:

• 0: BYTE. Samples are stored as signed bytes

• 1: FLOAT32. Samples are stored in IEEE 32-bit floating point format.

• VectorSimilarityFunction: a byte containing distance function used for similarity calculation.

• 0: EUCLIDEAN distance. (VectorSimilarityFunction.EUCLIDEAN)

• 1: DOT_PRODUCT similarity. (VectorSimilarityFunction.DOT_PRODUCT)

• 2: COSINE similarity. (VectorSimilarityFunction.COSINE)

• 3: MAXIMUM_INNER_PRODUCT similarity. ( )