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Lucene has four underlying types that a docvalues field can have. Currently Solr uses three of these:

  1. Wiki Markup
    NUMERIC: a single-valued per-document numeric type. This is like having a large long\[\] array for the whole index, though the data is compressed based upon the values that are actually used.

    • For example, consider 3 documents with these values:
      No Format
             doc[0] = 1005
       doc[1] = 1006
       doc[2] = 1005
      In this example the field would use around 1 bit per document, since that is all that is needed.

  2. Wiki Markup
    SORTED: a single-valued per-document string type. This is like having a large String\[\] array for the whole index, but with an additional level of indirection. Each unique value is assigned a term number that represents its ordinal value. So each document really stores a compressed integer, and separately there is a "dictionary" mapping these term numbers back to term values.

    • For example, consider 3 documents with these values:
      No Format
             doc[0] = "aardvark"
       doc[1] = "beaver"
       doc[2] = "aardvark"
      Value "aardvark" will be assigned ordinal 0, and "beaver" 1, creating these two data structures:
      No Format
             doc[0] = 0
       doc[1] = 1
       doc[2] = 0

       term[0] = "aardvark"
       term[1] = "beaver"

  3. SORTED_SET: a multi-valued per-document string type. Its similar to SORTED, except each document has a "set" of values (in increasing sorted order). So it intentionally discards duplicate values (frequency) within a document and loses order within the document.
    • For example, consider 3 documents with these values:
      No Format
             doc[0] = "cat", "aardvark", "beaver", "aardvark"
       doc[1] =
       doc[2] = "cat"
      Value "aardvark" will be assigned ordinal 0, "beaver" 1, and "cat" 2, creating these two data structures:
      No Format
             doc[0] = [0, 1, 2]
       doc[1] = []
       doc[2] = [2]

       term[0] = "aardvark"
       term[1] = "beaver"
       term[2] = "cat"

  4. Wiki Markup
    BINARY: a single-valued per-document byte\[\] array. This can be used for encoding custom per-document datastructures.