Non-volatile, Faster than DRAM: The Next Big Thing?
We're always looking for "the next big thing." See why that might be non-volatile RAM at massive scale.
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A few years ago I was asked to take part in a panel session at a conference. One of the questions asked by the audience was what we thought the “next big thing might be.” Most of the panel talked about software, after all it was a software conference and we were all software people. I recall people talking about Functional Programming and the addition of Lambdas to Java amongst other things.
At the time this was not long after HP had announced that they had cracked the Memristor, and my answer was “Massive scale, non-volatile RAM.”
If you are a programmer, as I am, then maybe that doesn’t sound as sexy as Functional programming or Lambdas in Java, but let me make my case…
The relative poor performance of memory has been a fundamental constraint on how we design systems pretty much from the beginning of the digital age.
A foundational component of our computer systems, since the secret computers at Bletchley Park that helped us to win the second world war is DRAM. The ‘D’ in DRAM stands for Dynamic. What that means is that this kind of memory is leaky. It forgets unless it is dynamically refreshed.
The computers at Bletchley Park had a big bank of capacitors that represented the working memory of the system and this was refreshed from paper-tape. That has been pretty much the pattern of computing ever since. We have had a relatively small working store of DRAM, backed by bigger, cheaper, store of more durable non-volatile memory of some kind.
In addition to this division between the volatile DRAM and non-volatile backing storage, there has also, always been a big performance gap.
Processors are fast with small storage, DRAM is slow but stores more, Flash is VERY slow but stores lots, Disk is even slower, but is really vast!
Now imagine that our wonderful colleagues in the hardware game came up with something that started to blur those divisions. What if we had vast memory that was fast and, crucially, non-volatile.
Pause for a moment, and think about what that might mean for the way in which you would design your software. I think that this would be revolutionary. What if you could store all of your data in memory, and not bother with storing it on disk or SSD or SAN. Would the ideas of “Committing” or “Saving” still make sense? Well, maybe they would, but they would certainly be more abstract. In lots of problem domains I think that the idea of “Saving” would just vanish.
Modern DRAM requires that current is supplied to keep the capacitors, representing the bits in our programs and data, charged. So when you turn off your computer at night it forgets everything. Modern consumer operating systems do clever things like implement complicated “sleep” modes so that when you turn off, the in-memory state of the DRAM is written to disk or SSD. If we had our magic, massive, non-volatile storage, then we could just turn off the power and the state of our memory would remain in-tact. Operating Systems could be simplified, at least in this respect, and implement a real “instant-on.”
What would our software systems look like if they were designed to run on a computer with this kind of memory? Maybe we would all end up creating those very desirable “software simulations of the problem domain” that we talk about in Domain Driven Design? Maybe it would be simpler to avoid the leaky abstractions so common with mismatches between what we want of our business logic and the realities of storing something in a RDBMS or column store? Or maybe we would all just partition off a section of our massive-scale non-volatile RAM and pretend it was a disc and keep on building miserable 3-tier architecture based systems and running them wholly in-memory?
I think that this is intriguing. I think that it could change the way that we think about software design for the better.
Why am I talking about this hypothetical future? Well, Intel and Micron have just announced 3D XPoint memory. This is nearly all that I have just described. It is 10 times denser than conventional memory (DRAM), it is 1000x faster than NAND (Flash). It is also 1000x better endurance than NAND, which wears out.
This isn’t yet the DRAM replacement that I am talking about. That is because although this memory will be a lot denser than DRAM and a lot faster than NAND it is still a lot slower than DRAM, but the gap is closing. If the marketing specs are to be believed then the new 3D XPoint memory is about 10 times slower than DRAM and has about half the endurance. In hardware performance terms, that is really not far off.
I think that massive scale non-volatile RAM of sufficient performance to replace DRAM is coming. It may well be a few years away yet, but when it arrives I think it will cause a revolution in software design. We will have a lot more flexibility about how we design things. We will have to decide explicitly about stuff that, over recent years, we have taken for granted and we will have a whole new set of lessons to learn.
Published at DZone with permission of Dave Farley, DZone MVB. See the original article here.
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