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A senior engineer's guide to the system design interview

interviewing.io

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Re: A senior engineer's guide to the system design interview

#171

Post by Wagthesam »

mgraczyk wrote: post #149
yunwal wrote: post #127

Earlier quoted context omitted.

> People with real experience will have encountered this problem and know that you have to spend time investigating to find the root cause of the backpressure, otherwise you could add capacity to random things without reducing the queue occupancy. Are your queue consumers getting throttled by some downstream service? Are your workers CPU bound? The "right" answer here is basically "we should figure out why the queue…

This might be true of SRE roles, but not really true for most engineers, particularly not where I currently work. I wasn't completely clear but what I'd be asking for here is how to predict and design for bottlenecks, not how to mitigate active disasters. Also making a queue bigger is a bad reflexive response to queues being full. I was very involved in the SEV review (postmortem) process at Facebook and witnessed lo…

do you work at google? most engineering roles ive been in engineers absolutely own their systems and take on call rotations.

I agree though, hasty response is the mark of a junior eng

Re: A senior engineer's guide to the system design interview

#172

Post by l8again »

azornathogron wrote: post #30
rednerrus wrote: post #9

We've gone away from system design interview questions on my team. We ask people to diagram something technical they understand well and the team digs in and asks questions to understand depth and breadth of the candidates understanding. For us it works much better. It's a chance to see how well candidates do in following instructions. It gives you a chance to explore depth and breadth of their knowledge on something…

I like this... in theory. But I don't think I'm allowed to give you a system diagram and detailed explanation of systems I've worked on, because obviously they're proprietary. That seems like a problem. How do your candidates normally work around this? Does everyone just talk about hobby or open-source systems they've worked on?

In my first semester as a freshman in an American university, I took a quiz in the Calculus class that had a question based on American football. Having never played the sports or even knowing the rules all that well, I aced the exam.

Yes, it is not that hard to keep the proprietary business logic separate from the system design.

Re: A senior engineer's guide to the system design interview

#173

Post by stale2002 »

rco8786 wrote: post #103
eschneider wrote: post #92

Earlier quoted context omitted.

98% of what you'd be inclined to diagram out and explain for a system design interview isn't remotely proprietary. People are generally looking for a high-level overview of a system you've worked on to see a) that you've really worked on it and b) you can explain it such that it makes sense. Sure, folks will ask you to drill down here and there for more detailed info, but if someone pokes on something where the detai…

> 98% of what you'd be inclined to diagram out and explain for a system design interview isn't remotely proprietary Maybe we're just on different wavelengths, but literally every single thing I work on that would be a good candidate for this sort of interview is extremely proprietary...and I'm just working on regular ol' backend services at [generic big tech].

If the entirety of your web development knowledge is NDA'ed, then what good are you as a potential employee anyway?

You wouldn't be able to build anything, as all your knowledge is NDAed!

Re: A senior engineer's guide to the system design interview

#174

Post by thdc »

A senior interviewer's guide to the system design interview*.

I've speed read over the existing two sections and while it's informative, I'd argue that the maybe 10+/12 of the core design concepts are things that someone with a formal CS education should have picked up - you don't need to be a senior software engineer.

The barrier is knowing how these things can be pieced together to make a system from scratch which is the more difficult part as it is a much rarer occurrence in most people's experiences. Even seniors may not have much experience in setting up large scale systems (depending on your definition of senior), so at the end of the day anyone that studied or memorized the material is good enough to pass - practical experience or not.

I'd much rather have a high level view of an existing or theoretical system, be provided with some issue that occurs, and be asked for ways to diagnose and remediate said issue. Forget the dance around setting the system up. This is similar to the practice of providing existing code in an interview, describing a bug with the code, and watching the interviewee debug and fix it - but with systems. It mirrors actual work more closely.

Re: A senior engineer's guide to the system design interview

#175

Post by lhorie »

nonethewiser wrote: post #148
lhorie wrote: post #99

Earlier quoted context omitted.

The way it typically fall aparts for my candidates is I ask about optimizations, they say X could be cached, then I ask about cache invalidation and lo and behold, it didn't even occur to them that the cache needs to be invalidated at some point, so they blurt something along the lines of doing the entire expensive operation again and checking it against the cache, or something similarly nonsensical. More common than…

Isn’t it better to know you can add a cache to reduce latency, even if you’re not sure how to invalidate it?

The problem isn't demonstrating understanding of what a cache does conceptually, in fact any SWE worth their salt ought to be able to explain caching. The problem is if the candidate's decision to add a cache causes the system behavior to become obviously incorrect upon an ounce of further inspection, because this demonstrates a lack of foresight about local maxima vs global maxima, and systems are all about trade-offs at the macro scale.

Caching is an easy thing to blurt out in an interview setting, but not all problem spaces benefit from caching and caching often isn't the only available solution, or the most ideal one.

Re: A senior engineer's guide to the system design interview

#177

Post by blue039 »

hot_gril wrote: post #156
blue039 wrote: post #112

Earlier quoted context omitted.

Yeah, I don't think I want a job that asks such questions. I've done the webscale BS. I've done actual architecture that exists in reality. At this stage in my career there's nothing an interviewer can do but insult me. You might say that this is hubris about my own skill but it has nothing to do with how good I am. My resume has a LOOONG track record of consistent work in the industry. Call my references, do some ac…

Companies already look at resumes, and the interview is a good way to double check things in a pass/fail manner. It's not like the SAT where you take a single test that sorta determines where you go, but even that is useful as a broad measure. Like if I'm in a top school's admissions and see 1800/2400 (idk the new scoring), there'd better be an explanation. If Amazon saw my resume and I couldn't explain to them gener…

These interviews are not gutchecks. They are shibboleth checks.

I can design you a nice document, do the research, put the pieces together, etc with the big picture. I may not know a ton about AWS or another cloud provider but I can put the document together that describes how it will be looking when it's done. That is architecture. Somewhere between UML and word documents.

What these interviews are checking, and the one you are describing, is whether or not I can parrot the correct code-words. Lambda, elastic cache, all this other nonsense. That's the purpose of the bloodsuckers I mentioned above. If you can train someone with little architecture experience to pass a senior level interview by just saying the right things and knowing the right hype tech then you're not hiring architects you're hiring grifters.

It's a problem that is endemic in this industry. You can't "gut check" 30 years of architectural experience unless you're legitimately asking the core questions of architecture. Every interview I've been in has had me studying stupid buzzwords from cloud technology and every interview I am asked how to use these technologies. As an example, I was once turned down because I didn't use Kafka. I knew what the underlying technology was and suggested using it but the fact I didn't say kafka eliminated me. The reason? I can only guess, but it's likely because the interviewer doesnt know much and was looking for a way to get into a debate over kafka vs protobuf vs whatever instead of discussing actual planning of a system. These debates are resolved after I take the problem back to my desk and think about it for a week. Not in an hour. In an hour the best I can give you is a block diagram with maybe some very rough fleshed out detail.

The humility check should be bi-directional. It has been my experience that interviewers tend to be the least humble people at a company. The power dynamic is obvious and it's not in the character at most startups where a "senior" engineer high on hopium can settle themselves into their rightful place.

Re: A senior engineer's guide to the system design interview

#178

Post by kimburgess »

Since we’re talking systems here and reasoning from some provided constraints:

> We began by listening to 30+ hours of system design interviews and system design lessons. We then performed data analysis to identify 50+ of our highest rated interviewers.

At an average 30 mins an interview, that’s 60 interviews in the data set this is based on. That seems like a disproportionate sample to form general advice. That doesn’t mean it’s bad, but does likely bias heavily to a subset of system/interview styles.

Re: A senior engineer's guide to the system design interview

#179

Post by Plasmoid »

mgraczyk wrote: post #53

I am on the interviewer side of ~1 system design interview per week and have done probably around 100 of them at Google and other companies. Most of the advice here is good, although it could be condensed quite a bit. The biggest red flag for me as an interviewer is when candidates list off concepts or technologies they don't understand. DO NOT say things like "we can't do this because of the CAP theorem" or "we shou…

A cache is such a red flag when I'm doing a system design interview.

I ask people to design a system but the system itself is very write heavy. Like 50 writes per read imbalanced. People will often suggest a cache because it's in the standard interview prep but not actually think about why they need it. They just go right to "I need a cache somewhere".

Re: A senior engineer's guide to the system design interview

#180

Post by ramraj07 »

rednerrus wrote: post #9

We've gone away from system design interview questions on my team. We ask people to diagram something technical they understand well and the team digs in and asks questions to understand depth and breadth of the candidates understanding. For us it works much better. It's a chance to see how well candidates do in following instructions. It gives you a chance to explore depth and breadth of their knowledge on something…

How many rounds of interviews do you typically do? What other interviews if any? Curious what good orgs are doing in this regard!
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