I want to have search results from SOLR ordered like this:
All the documents that have the same score will be ordered descending by date added.
So when I query solr I will have n documents. In this results set there will be groups of documents with the same score. I want each of this group of documents to be ordered descending by date added.
I discovered I can accomplish this using function queries, more exactly using rord function http://wiki.apache.org/solr/FunctionQuery#rord, but as it is stated in the documentation
WARNING: as of Solr 1.4, ord() and rord() can cause excess memory use since they must use a FieldCache entry at the top level reader, while sorting and function queries now use entries at the segment level. Hence sorting or using a different function query, in addition to ord()/rord() will double memory use.
it will cause excess memory use.
What other options do I have ?
I was thinking to use recip(ms(NOW,startTime),1,1,0). Is this the best approach ?
Is there any negative performance impact if I use recip and ms ?
You can use multiple SORT conditions:
Multiple sort orderings can be separated by a comma, ie: sort=+[,+]...
http://wiki.apache.org/solr/CommonQueryParameters
So, in your case would be: sort=score DESC, date_added DESC