Is there a good way to join data from SOLR indices ? Of course, I assume server side support for this is limited, but i want to do it client side (right now, im manually doing this in java, using hashmaps and loops .... Im assuming there might be a better way to combine data from different indices).
If with join you mean relational joining a la SQL, then no.
If with join you mean merging then server side support is far from limited.
What you are looking for is index sharding.
This is not "fast" since searches are distributed and then merged, but it scales really well.
Give a read to the following articles:
