How to use vmtouch - the Virtual Memory Toucher to keep file or files in memory to super speed-up their access. Eg: sqlite database file or critical web-server resources.
How to keep a file in memory
vmtouch -vt file.dat
How to evict a file from memory
vmtouch -ve file.dat
How to daemonise and lock all files in a directory into physical memory
vmtouch -dl /opt/app