For random gets:
- decrease the block size, not more than 64kb, 32k should be good
- add a bloom filter on your table, at the row level
- split your table in multiple regions by setting a low region file max to 1Go or lower and presplit your table (by country, merchants, or whatever you want)
- activate the in memory
- use a fast compression codec (lzo or snappy are good)
- use a tablepool on your client side
- use memcache (...)
Enjoy ;)