Heikki's experiments with ranking

Personal notes, likely to be out of date.

Things to experiment with, and find out, and mess about

Goals:
 - Understand the ranking
 - make a better ranking merging algorithm




Tue 19-Nov-2013 Started this branch


Wed 20-Nov-2013 Make a script that tests ranking against yaz-zserver
(as that is the default config). Mostly to have a script to build on later.

Thu 21-Nov-2013. Start my own complete config

Fri 22-Nov-2013. Adam defined a new sort type, relevance_h, and put it place
in the code. Now I have a place to implement my stuff. Relevant places:
 pazpar2_config.c:1020  - minor
 session.c:1318 - call relevance_prepare_read also for my type
 reclists.c:104 - parse params
 reclists.c:166 - compare function (for quicksort)
 relevance.c:417 - calculate score
         (same function as for relevance, but with extra arg for type)

The compare function compares positions, when sorting by Metadata_sortkey_position
This loops through the records (in the cluster) and finds the smallest rec->pos
and then compares those.

Next: See if I can implement a round robin.
 - clients.h declares int clients_count(void)
 - rec->client is a pointer to the client, but we don't have an ordinal from that
   - keep an array of structs with the pointer, and locate the client number that way
 - robin-score = pos * n_clients + client_num