Creating a DocValue Field
Similar to a stored field, DocValue is a part of a document. It's also created at indexing time, and contains value that are specific to a document. The major difference between the two concerns their underlying storage structure. The field's storage is row-oriented, whereas DocValue's storage is column-oriented. In retrieval, all field values are returned at once per document, so that loading the relevant information about a document is very fast. However, if you need to scan a field for any other purpose it will be a slow process, as you will have to iterate through all the documents and load each document's fields per iteration. The DocValue is stored by column in DocId to value mapping, and loading the values for a specific DocValue for all documents at once can be done quickly, as Lucene only has to scan through one column rather than iterating through each document to load a field. In summary, the field and DocValue both contain information about a document...
