[sqlite] Read data from database slow the first time but then very fast thereafter. How can I improve the speed for the first time read?

[Linquan Bai]

I am trying to read large data from the database about 1 million records.
It takes around 1min for the first time read. But if I do the same process
thereafter, the time is significantly reduced to 3 seconds. How can I get a
fast speed for the first time read?
Hope to received your valuable suggestions.
Thanks!