Hi Markus, I confirm (if that counts) that all current built-in similarities (expect Sweet spot) save same stuff into the norms.
They can be switched/changed at search time. Actually, I am doing this today with Lucene, experimenting different term-weighting models using a single index. It would be impractical to create a dedicated/separate index for each term weighting model (similarity). Only assumption here is, their discountOverlap should remain same with the one used at index time. But of course we cannot make any assumptions regarding custom similarity implementations. As Hoss pointed out, discountOverlap affects the way document length calculated. It cannot be changed on the search time. Thanks, Ahmet On Tuesday, December 15, 2015 9:43 PM, Chris Hostetter <hossman_luc...@fucit.org> wrote: : Sweetspot does require reindexing but is that the only one? I have not : investigated some exotic implementations, anyone to confirm sweetspot is : the only one? In that case you could patch QueryComponent right, instead : of having a custom component? I'm not sure how where this thread developed this weird assumption that switching from/to SweetSpotSimilarity in particular requires reindexing but that many/most other Similarities wouldn't require this ... SweetSpotSimilarity certainly has explicit config options for tuning the index time field norm, but it's not a special case... 1) Solr shouldn't make any naive assumptions about whatever arbitrary (custom) Similarity class a user might provide -- particularly when it comes to field norms, since the all of the Similarity base classes / callers have been setup to make it trivial for people to write custom ismilarities for the express purpose of adjusting how many bits are used by field norms. 2) In both ClassicSimilarity and BM25Similarity (the new default in Solr6) the config option "discountOverlaps" impacts what norm values get encoded at index time for a given field length -- so it's possible to break things w/o even switching what class you use, w/o even consider custom Similarity impls (or new out of the box similarity classes that might be added to Solr tomorow) -Hoss http://www.lucidworks.com/
