Hi, 2015-08-12 17:46 GMT+02:00 Sanne Grinovero <sa...@hibernate.org>: > That's an interesting proposal, as index sharing inherently implies > that fields on different types shall not have conflicting mapping > (i.e. don't reuse the same field name for a different type). > > By default we don't share indexes across unrelated types, but also *by > default* subtypes are indexed in the same index as their parent - if > the parent is indexed as well.
Yes, I think that's the case where it makes sense. It'd make sense to re-phrase the docs in that regard. > > The reason is to efficiently map a polymorphic domain: when people > search for type X, they implicitly also search for its subtypes as > these are valid candidates for the query. > Having them all in the same index makes for better result quality and > better search performance - as joining multiple IndexReaders to > perform a cross - index Query is generally a bad idea, as it's then > hard to accurately normalize statistics across different vector > spaces, and that's what defines the quality of the search result. > At least I believe that *generally* that would give you better > results, but that's why we give options, and also why sometimes people > might want multiple Domain objects to be stored in the same index: > they might be "subtypes" from a domain perspective even if they don't > technically use inheritance at the Java level: they might be different > types and yet be mapped to some common fields with (hopefully) > compatible indexing options. Have you ever seen this as an actual requirement by someone? > > If we were to drop index sharing, then I think it should be fair to > also not support multiple types as target for a query anymore; as I'm > assuming in this case you'd only share for subtypes of some common > parent, and you'd target that common parent exclusively to perform a > polymorphic query. Assuming we'd drop index sharing for unrelated types but would continue to support it for the types of one inheritance hierarchy, one still might want results only from a sub-set of the hierarchy's types. > > So that's the reasons for which it exists; there are some good reasons > to not allow it too: as you mention the filtering, but also the very > fact that the type information has to be stored in form of classname > (typename, in free-form). Interestingly, that's not so much an issue with ES. There you always add a "type" discriminator. > I think the strongest reason to not allow it is to avoid the > inconsistent field mappings, but we could compensate for that with > better schema validation - something which seems is getting more > necessary anyway. Yes, that' help. All in all, index sharing for inheritance hierarchies makes sense to me, but I am doubtful about sharing between unrelated types. > > I didn't mean to kill the proposal :) just hoping it helps figure out > why someone might need it. Would be nice to think of alternatives out > of the box to avoid the filtering. > > Sanne --Gunnar > > > > On 12 August 2015 at 15:30, Gunnar Morling <gun...@hibernate.org> wrote: >> Hibernate Search aficionados, >> >> I am wondering what that's the rationale for offering the feature of >> index sharing [1]. >> >> The ref guide says "there is really not much benefit in sharing >> indexes". It complicates queries, as an additional filter on the type >> field must be applied in case of targeting only one entity using a >> shared index. >> >> Should we consider to drop this feature in HS 6? >> >> Thanks, >> >> --Gunnar >> >> [1] >> https://docs.jboss.org/hibernate/search/5.4/reference/en-US/html_single/#section-sharing-indexes >> _______________________________________________ >> hibernate-dev mailing list >> hibernate-dev@lists.jboss.org >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > _______________________________________________ > hibernate-dev mailing list > hibernate-dev@lists.jboss.org > https://lists.jboss.org/mailman/listinfo/hibernate-dev _______________________________________________ hibernate-dev mailing list hibernate-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev
