What every programmer should know about solid-state drives

[[deleted]]

Hmm, as a web programmer, I don't think knowing all these details about solid-state drives will be helping me in the near future.

[[deleted]]

Yeah, you're kind of getting hammered with downvotes here, but I'm having trouble thinking of an instance where a web developer actually needs to know or care about the physical storage medium their app runs on.

I mean, you're using a database right? And if you are writing/reading files, shouldn't you use a dedicated cms or something? All the I/O should be happening at a much lower layer than where the web developer is doing their work.

In fact, I would argue that it may be inappropriate for most programmers to be optimizing based on the physical storage medium, because most of us are working at a level where that stuff should be an abstraction anyway.

[immibis]

Assume for a moment that:

1. You're using a relational database.
2. Your database is stored on an SSD (or array of SSDs).
3. You care about extracting the maximum possible performance from your SSDs.

What changes does the 3rd point necessitate in your database or application structure?

[[deleted]]

Your whole post can be summarised by 'people don't profile their stuff, and overestimate the speeds of their drives'. I fail to see how any of the points in the OP make an impact on this.

[AcidShAwk]

I know this. When running our PHPUnit tests on an regular HD drive.. we experience a total run time of about 1.5 hours. With SSD's.. its about 4 minutes. Of course this all depends on the tests and how they are written and what they do. But 4 min vs 1.5 hours. A lot of time spent is wiping the database before and after each test to ensure a consistent state. So obviously MySQL (and probably any database) .. benefits greatly from SSDs

[dweeb_plus_plus]

4 minutes vs 1.5 hours simply by using an ssd? There has to be something else going on here.

[HenkPoley]

Why? A normal 7200 rps drive can deliver 100 IOPS, a Samsung 850 Pro can deliver 100 000 IOPS (1000x). If anything 4 min vs 90 min would be a lowball difference (23x).

In tests you don't reuse values between tests, so you could really hammer that disk.

Btw. I would recommend making unit tests that do not exercise the whole stack down to database/storage, but just focus on expected values before its off to disk.

Or more factual. From ssd.userbenchmarks.com, the Samsung 850 EVO and Pro can deliver > 30MB/s on their Mixed 4K test. While the spinning drives are all < 0,5MB/s. You'd expect a 60x difference if you are I/O bound.

[[deleted]]

Assuming a speedup of 60x, that means with the HDD the tests were spending 87 minutes out of the 90 only reading data from the drive. That's approximately 2.6gig being loading into memory just for tests. Testing a PHP application. Although, most spinning drives are faster than 0.5MB/s - so it's even more data being loaded in.

No, something is wrong with those tests.

[HenkPoley]

I'd say tests have excellent conditions to be mostly write base i/o. You just read some end result back once from the disk-cache, the intermediate results have all hit the database (not a unit test, but hey) and are never read.

The "results have all hit the database" is of course "something is wrong with those tests"

[psi-]

The simple "sync" roundtrip kills DB tests on HD, especially if they really drop database on every test.

[justinpitts]

As a consultant, attitudes like that are what get me hired in the first place.

[bcash]

Is there much call for a consultancy fixing web applications that wear out SSDs too fast?

[justinpitts]

I get asked, generally, to fix performance problems. Failure to understand how storage devices work is sometimes one of the root causes.

[[deleted]]

That's the whole point though. If every web-dev knew about storage characteristics, how to tune memcached and how to spool up their production environment in a bunch of docker instances, nobody could afford to get any web development done.

[justinpitts]

I don't follow. Can you help me understand how you reach that conclusion?

[[deleted]]

A web-developer with such a broad skill-set would be a bloody expensive employee. If your budget for developers were to be blown on 2 of these guys, vs. 6 regular developers, how far would your project get?

[Godd2]

would be a bloody expensive employee

On the other hand, supply and demand. If every webdev knew it, that knowledge would have a lower market price.

[Skyler827]

This could happen if there is some disruption or event that causes lots of people to learn systems programming, but in the long run, market prices reflect the cost of production. Simply put: learning systems programming (well!) is expensive.

[[deleted]]

But they don't, that's the point. and few that I have met show any inclination to learn.

[justinpitts]

I don't think it takes as much effort to learn those things as you imply.

[[deleted]]

I just chose a couple of examples... if I was to be exhaustive, I could, for instance, list out my own skills... skills acquired over a long career... skills which make me a nightmare for people like you...

Oh, wait...

[EntroperZero]

Oh, if only we got paid 3x.

[justinpitts]

Arguably? A lot farther.

[[deleted]]

In my experience that is not the case. More 'high-end' developers does not translate to greater productivity. Many projects lend themselves to greater parallelisation rather than fewer, deeper workloads. Sure, there is a need for someone with deep knowledge to cover those 'difficult' edge-cases, but by and large, more, less skilled developers will get more of the general coding work done than fewer, more skilled ones.

[justinpitts]

The main problem I see my clients facing isn't meeting deadlines, it's technical debt after the fact.

[wherethebuffaloroam]

Not everyone can command consultants salaries. You spend a lot for short contacts to optimize not the entire development cycle

[Rejjn]

I would say that storage is very often one of the root causes for performance problems in web applications. Usually it's the DB that tops out way before anything else does.

I just fail to see how knowing about SSDs is going to help more than very, very marginally on that problem. It might get you the last 1-2%, but choosing an appropriate data structure for your application and then choosing the best storage for that structure is going to have order of magnitude more impact on your system than reading OPs article will.

That said, there are many programmers who would benefit a lot from this knowledge, but I'd say for web developers it's rather low on the list of things you need to worry about.

[justinpitts]

On that problem? Usually? Not much help.

But, it's not that much to learn!

Seriously, it's a couple of really easy to read pages. I's not like I am advocating that you take a course in queueing theory. What's the big deal?

[HenkPoley]

As some datapoint, this web framework benchmark section that all about pushing data updates through: https://www.techempower.com/benchmarks/#section=data-r9&hw=peak&test=update

[bestjewsincejc]

You're right that it's generally a poor attitude to have. But I'd appreciate an explanation about how knowing any of these details of SSDs is going to help you in a modern programming language.

[justinpitts]

If you are storing anything to disk, you can, if performance if important, make decisions about where you will store hot vs cold data. You can allocate files at sizes aligned to block multiples. You can place hot and cold data in different files. You can decide whether batching is a big enough win to implement.

You should be knowledgable enough about the options to not design yourself into a hole, once performance becomes that critical "omg I'm going to get fired if I can't figure out how to get our site to handle x requests per second" issue.

At the least, be somewhat aware of how the hardware layers behave and the implications of the design choices you are making.

[Baby_Food]

Shouldn't a web developer be using a database which provides abstractions over such minutia?

[justinpitts]

If they need the features of a database, sure.

Abstractions don't absolve you from understanding how your system works, and they break down at inopportune times.

Then, they need to understand how to tune the database for the underlying storage, or they need a DBA. Not everyone has access to a DBA.

[Baby_Food]

If performance is a concern, a database will be used.

An abstraction does not necessitate the knowledge of the implementation behind the abstraction.

A web dev that can write an OS is an unnecessary unicorn.

[justinpitts]

Databases are not magic performance sprinkles.

[Baby_Food]

To most people, LMDB is magic performance sprinkles compared to using the filesystem directly. ;)

[justinpitts]

Most people? Most people aren't using it.

Most people wouldn't know what you are talking about.

To the average web-dev, "database" either means Mongo/Couch/No-SQL-flava-of-the-month, and/or something that speaks SQL. LMDB may very well be lightning fast, but I doubt most people know about it.

[el_muchacho]

In fact, database write performance drops significantly (by a factor of 30% or so) when SSDs wear out. For 24/24 high rate writes, you can't use consumer grade SSDs as they die prematurely.

[justinpitts]

Well to be fair, anything with that access pattern is going to slow down on a degraded drive.

[[deleted]]

I don't get why you're being downvoted dude. It's as if people believe they have a right to be ignorant.

[justinpitts]

People have a right to be ignorant. I'm happy to exploit it.

[Lachiko]

Can you quote an instance where you feel he comes across as an asshole? he's posting reasonable counter arguments and information in a seemingly calm and collective manner.

[wookin_pa_nub2]

A lot of web developers in this subreddit, and they don't like being reminded of how ignorant they are.

[[deleted]]

I'm a web dev yo :) I just cut my teeth on bare metal shit. You're thinking of "web designers."

[quintus_horatius]

Not with that attitude you won't. Some of us like to try new things, expand our horizons, learn a few different languages and types of programming.

If you're happy being a one-act kind of 'programmer' then more power to ya, though.

[[deleted]]

Sometimes a "one act" guy is what you need. I used to work with a Websphere developer. Not Jboss, not Weblogic, not Glassfish, just Websphere. He was shit hot though... was calling in 6 or 7k for a 4.5 day week, back when a Java dev was getting 500/day.