Your operating includes a page cache (in some cases it may have even more e.g., ZFS on Solaris with ARC). It can very effectively load these indexed values into

Your operating includes a page cache (in some cases it may have even more e.g., ZFS on Solaris with ARC). It can very effectively load these indexed values into memory. Of course your own cache and direct I/O may be more efficient if you're building a search index or a relational database, but for a key/value store the page cache should be very effective.