Hi @wchu, thanks for your reply. I am comparing these two because writing a new data sets hits the disk - to persist the data to the ssd device. On top of that there is event a minor penalty of updating the secondary index (in memory). Yes, if I am writing the data first only later adding the index (as you are suggesting) , I am experiencing the same high io and long time to read the data and creating the index. What I am asking why is there in Aerospike such a big difference in terms of elapsed time and io usage between writing the data (persisting to SSD) and reading it when creating the secondary index.
I conclude the elapsed times of primary index and secondary by looking at the log messages. They were explained here.