Yes, surprisingly enough, if indexed=false, docValues=true — you can still search. I’ve seen the code behind it; it’s interesting. Rob wrote it. I’m not sure how scalable it is compared to the inverted index. I suspect it wouldn’t do well for a lot of distinct values but will fine for a small number of them. What definition of “small” though… I don’t know. I’d love to see benchmarks of such a comparison.
~ David Smiley Freelance Apache Lucene/Solr Search Consultant/Developer http://www.linkedin.com/in/davidwsmiley On Thu, Apr 9, 2015 at 8:30 PM, Erick Erickson <erickerick...@gmail.com> wrote: > So I was a bit embarrassed to be asked whether there was a use-case > for this. I did some simple tests on a field (with a magnificent total > of 32 docs indexed) and, with the exception of an error that > facet.mincount=0 doesn't work if a field isn't indexed (see > SOLR-5260), everything I tried worked fine. Searching by wildcards, > searching with the term query parser, faceting, grouping, whatever. I > admit I didn't spend very much time looking. > > As I understand it DocValues are basically a serialized UnInverted > field so I'm wondering how searches work at all. Or, more > specifically, whether this works fine on small numbers of docs but > wouldn't scale. Or does a search on a DocValues field build an > inverted field? > > Or anything else I should know. Is the rule simply 'if you search on > it, or use it in fq clauses, set indexed="true", and if you facet, > group etc. set indexed="true" '. So it would make sense to set > docValues="true" and indexed="false" on a field that's never searched > or used in an fq clause but used for faceting & etc. > > So my mental model is "some operations need inverted fields, and some > need uninverted fields" and that docValues provide a way to store > uninverted fields on disk just like indexed="true" allows you to store > inverted fields on disk. Assuming you need both and set both > indexed="true" and docValues="true", the _total_ memory requirements > for Solr are the same. What's NOT the same is that the docValues make > use of MMapDirectory where uninverting a field doesn't (this last is a > total guess). > > I'm preparing a Google Doc that I'll certainly permit to anyone who > wants to add to it. I'll then add the results into the Reference > Guide. > > Anyway, you can see I'm confused, but if I ask enough silly questions > eventually my questions get less silly. > > Erick >
