Question
In Lucene if you had multiple indexes that covered only one partition each. Why does the same search on different indexes return results with different scores? The results from different servers match exactly.
i.e. if I searched for :
Partition 0 would return a score of 0.345
Partition 1 would return a score of 0.337
Both match exactly on name and DOB.
Solution
The scoring contains the Inverse Document Frequency(IDF). If the term "John Smith" is in one partition, 0, 100 times and in partition 1, once. The score for searching for John Smith would be higher search in partition 1 as the term is more scarce.
To get round this you would wither have to have your index being over all partitions, or you would need to override the IDF.
Solution
Because the score is determined on the index if I am not completely mistaken.
If you have different indexes (more/less or different data that was indexed), the score will differ:
http://lucene.apache.org/core/3_6_0/scoring.html
(Warning: Contains Math :-))