Yes. It takes your hardware about 3 seconds to read through 700M of ram.
Keep in mind that you're not just reading RAM. You're pushing system
requests through the VFS layer of your operating system, which is treating
the RAM like a disk (with cylinder groups and inodes and blocks, etc) so
you have all that processing overhead as well. What filesystem did you
format the RAM disk with?
tmpfs
Why are you doing this? If you have enough RAM to store the table, why
not just allocate it to shared buffers?
just allocating will make read from hdd to RAM at first time, to eliminate that
are you saying it will take 3 seconds surely if i have 50 lakh record