Now, that’s a disruptive change. Actually, it developed in the open, but still, I didn’t really think about it until today. We all have learned to love SSDs. My old company PCs used to boot for a couple of minutes, sometimes even for a quarter of an hour, before I could start my daily work. If you’ve got an SSD, that’s typically done in a minute, and if you’ve got a Mac, it’s a matter of seconds. The extreme being tablets and smartphones: Most of the time they run in stand-by, so they are just there when you need them.
Let’s think this to the end. Imagine that storing or retrieving data on your hard disk doesn’t take any perceptible time. Imagine that external storage of mass data isn’t your system performance’s bottleneck. What does this mean to programmers? What does it mean to hardware designers?
Actually, that doesn’t seem to be an utopia. Today I’ve learned that it’s possible to buy super-fast external storage plugged into your system’s PCIe bus. In other words: very close to your CPU. Flash memory – i.e. SSDs – are only the start. It’s fast, but NVDIMMs are way faster. Putting it in a nutshell, these are traditional RAMs backed by a flash memory, so they don’t loose data after switching the system off. If I’ve got it right, NVDIMMs are future tech, while PCIe flash memory is already there. It costs a lot, but it doesn’t seems to be an exotic technology. So let’s assume NVDIMMs were already there. Just for the fun of it.
Now for the exciting question: How does such super-fast memory affect us?
The idea is new to me, so I may have missed a lot of details, but it seems obvious to me that this is a game-changer.
For example, consider hardware design. It’s built on a hierarchy. Fast memory is scarce, but there’s an abundance of cheap and slow memory. So hardware designers started to invent caches. Later, they added a cache to cache the first level cache, and nowadays even third-level caches are mainstream technology. This continues at the hard disk level. Many hard disks employ caches themselves.
If mass storage was as fast as the CPU, all these optimizations were superfluous. Actually, they were a waste of energy, possibly even performance.
Software design would be affected, too. Software designers know that external storage is slow, so they try hard to keep all the data they need in memory – or, if you’re really power-hungry, in the CPU cache. A lot of thought went into finding ways how to keep your program and your data small. How to avoid database accesses. And so on. Mind you: would you implement your programs they way you do today if storing data in the database is just as fast as storing it in a temporary hash table?
My bet is that affordable NVDIMMs require us to redesign both our hardware and our software on all levels. For example, currently the programming API differs vastly if you write data to memory or if you write data to the hard disk. I suspect that’s one of the things that’d change with affordable NVDIMMs.
And what about database design? Technologies like SAP HANA indicate that databases running on RAM require – or allow for – a new programming model. SQL is optimized for relational databases running on slow memory. Databases that are as fast as the CPU may need a different optimization. For instance, many recent RAM-based databases are column-based, not row-based.
Did I make you curious? If so, I’d like to point you to the article I read this evening. As it seems, four guys had the opportunity to explore PCIe SSDs for four years and wrote an article about it. Highly recommended!
Oh, and one of the affected branches is the book industry. Almost every IT text book needs to be rewritten with the advent of super-fast external mass storage.