[Koha] Elasticsearch recent works at BibLibre

[Claire Hernandez]

Hi,

This week, some devs work together to move forward concretely on 
Elasticsearch issues encountered. You will find below a focus on some 
points (some are at poc state today) written by Alex and Jajm from 
BibLibre. We would be glad to discuss these topics at hackfest in march 
and having user feedbacks too :)

#1 Proof of concept for language analyzers

bug 21357 - 
https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=21357#c32
It's an attempt at having a default ES configuration with stemming, 
elision, etc. that works with multi-languages catalogs
You can read the comments and patch for more information.

#2 Compatibilites for tomorrow

Compatibility with latest version of Search::Elasticsearch - 
https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=24552

Compatibility with Elasticsearch 7.x : Problem: Search::Elasticsearch is 
not yet compatible with ES 7.x, so we are stuck with
  ES 6.x (unless we use something else...)

#3 Querying Elasticsearch in a better way

POC query_string => boolean query 
https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=24555
This POC is about replacing the use of full text queries (query_string) 
with Boolean queries for biblio search

Advantage:
     => No search craches with special character ( "!", ")" etc...)
     => Separate query context and filter context:
          - Search scores are not altered by facets,
         - Ability to use range filter  (i.e for publication date facet)

Regards,
Claire.