It depends on what 50K users is doing. (if your cluster capacity and configuration is right, you can scale horizontally without any problem) If it is just the point lookup(key value access) then depending upon the disk(SSD/HDD) you are using, you should be able to scale without any problem, some basic configuration tweak is required, like increasing no. of handlers for datanode and regionserver, block cache/bucket cache etc If you are doing heavy scans then you may need a large cluster which can bear this load. Network, CPU and disk will play an important role. ... View more