Yes, you can simply mmap the index file. The index server have not to read the index at the start. The goal of query processing is to decrease the query latency

Yes, you can simply mmap the index file. The index server have not to read the index at the start. The goal of query processing is to decrease the query latency, this is why it is better/necessary to do partitioning. Each query can be processed simultaneously by all threads. Intersections are very costly for long posting lists.