What are docValues in Solr? When should I use them?

Question

So, I have read multiple sources that try to explain what \'docValues\' are in Solr, but I don\'t seem to understand when I should use them, especially in relation to indexed vs

Answer 1

Use cases of DocValues are already explained by @Persimmonium and are pretty clear. they are good for faceting and sorting and such fancy stuff in the IR world.

What are docValue and why they are there ? docValue is nothing but a way to build a forward index so that documents point to values. they are built to overcome the limitations of FieldCache by providing a document to value mapping built at index time and they store values in a column based fashion and it does all the heavyweight lifting during document indexing.

What docvalues are:

NRT-compatible: These are per-segment datastructures built at index-time and designed to be efficient for the use case where data is changing rapidly.

Basic query/filter support: You can do basic term, range, etc queries on docvalues fields without also indexing them, but these are constant-score only and typically slower. If you care about performance and scoring, index the field too.

Better compression than fieldcache: Docvalues fields compress better than fieldcache, and "insanity" is impossible.

Able to store data outside of heap memory: You can specify a different docValuesFormat on the fieldType (docValuesFormat="Disk") to only load minimal data on the heap, keeping other data structures on disk.

What docvalues are not:

Not a replacement for stored fields: These are unrelated to stored fields in every way and instead datastructures for search (sort/facet/group/join/scoring).

Use case to use with Lucene docValues this way.

    public Bits getDocsWithField(FieldInfo field) throws IOException {
  switch(field.getDocValuesType()) {
    case SORTED_SET:
      return DocValues.docsWithValue(getSortedSet(field), maxDoc);
    case SORTED_NUMERIC:
      return DocValues.docsWithValue(getSortedNumeric(field), maxDoc);
    case SORTED:
      return DocValues.docsWithValue(getSorted(field), maxDoc);
    case BINARY:
      BinaryEntry be = binaries.get(field.number);
      return getMissingBits(be.missingOffset);
    case NUMERIC:
      NumericEntry ne = numerics.get(field.number);
      return getMissingBits(ne.missingOffset);
    default:
      throw new AssertionError();
  }
}