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danluu's profile
Dan Luu
Dan Luu
Dan Luu
@danluu

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Dan Luu

@danluu

https://patreon.com/danluu 

danluu.com
Joined December 2008

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    1. Dan Luu‏ @danluu May 26
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      I'm starting to wonder if design interviews are not only useless, but actually contributors to poor design. I'm still thinking through this, by my reasoning for this is:

      5 replies 30 retweets 125 likes
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    2. Dan Luu‏ @danluu May 26
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      There've been times where I've reduced the implementation effort of something by 100x to 1000x, producing in 1 day something that replaced ~1 year of work (proposed or actual). This has never been with "design interview" reasoning, it's always been domain knowledge.

      2 replies 3 retweets 61 likes
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    3. Dan Luu‏ @danluu May 26
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      This doesn't mean you have to be a deep domain expert, in the two most extreme cases, it was something I came to pretty soon after starting work in a new (to me) field. But it was still after much more time than you get in a design interview.

      2 replies 1 retweet 13 likes
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    4. Dan Luu‏ @danluu May 26
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      Interviewers sometimes try to get around this by saying you should questions assumptions, etc., but I don't think this would have worked in either case. In one case, the solution resolved something that had been an open problem in IR for decades, that's not interview material.

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    5. Dan Luu‏ @danluu May 26
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      In the other case, the solution was to relax an unnecessary constraint. I think it would've been v. difficult to successfully challenge such a fundamental assumption in an interview, it's probably faster to just build the thing (which is what I did), but not feasible in interview

      2 replies 0 retweets 13 likes
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    6. Dan Luu‏ @danluu May 26
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      For my most recent design interview my answers to "how would you scale M up to limit A?" were, in descending order of preference (the interviewers thankfully didn't fail me for this): 1. Buy a solution from N that's known to scale up to 100x A

      1 reply 2 retweets 31 likes
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    7. Dan Luu‏ @danluu May 26
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      2. Talk to expert O, who has solved this problem before, ask for other experts to talk to and see what they have to say 3. Read the relevant bits on LWN and LKML, understand how the open source implementation of M by company P works 4. Run experiments, profile, read code, etc.

      1 reply 0 retweets 28 likes
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    8. Dan Luu‏ @danluu May 26
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      5. The usual design interview nonsense, boxes and arrows, Fermi estimates, say "pubsub" a few times, etc. The interviewers very patiently explained to me that solutions 1-4 were invalid and kindly didn't fail me for those (I think most would've), but what's the point of this?

      3 replies 0 retweets 13 likes
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    9. Dan Luu‏ @danluu May 26
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      I see a lot of systems that look like they were designed by skipping straight to step (5). Of course I can't prove a causal link from design interviews, but it seems plausible that design interviews train people to design real systems without understanding the problem domain.

      3 replies 3 retweets 38 likes
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    10. Dan Luu‏ @danluu May 26
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      People say these interviews "measure how you think", but @hillelogram has looked into the history for other kinds of interview questions, he found "how you think" was a post hoc rationalization for questions that were originally asked for other reasons. Likely same here.

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      Dan Luu‏ @danluu May 26
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      But even without looking at the historical record, "how you think" seems bogus To answer a Fermi estimation question, you just need to know how to play the Fermi estimation game. Make up numbers, multiply them together, and then you pass. Basically ditto for design interviews.pic.twitter.com/zoOU85g5ac

      On the hiring side, we found that brainteasers are a complete waste of time. How many golf balls can you fit into an airplane? How many gas stations in Manhattan? A complete waste of time. They don’t predict anything. They serve primarily to make the interviewer feel smart.
…
Fun fact: in business school, I got asked that exact brain teaser by some company (I can't remember who). "Can I take a minute?" I asked.
"Sure," said the interviewer. After a moment, I said, "nineteen". He looked confused.
"How did you get that answer?" he asked. I looked confused.
"I counted."
Presumably he hadn't been expecting to interview someone who grew up in Manhattan, went to school in the Bronx, and spent a lot of time driving around New York with her dad.
I didn't get the job. Apparently, they were looking for people who used some process other than arithmetic to figure out how many gas stations there were in Manhattan.
      7:44 PM - 26 May 2020
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      6 replies 14 retweets 85 likes
        1. Tim Fox‏ @timfox May 27
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          Replying to @danluu

          I extend this to all technical interviews - they're an elaborate charade that adds nothing. May as well just filter applicants by resume+experience, randomly sample them and have one F-F interview (non technical) to check they're not impossible to work with.

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        1. Hillel‏ @hillelogram May 27
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          Replying to @danluu

          Hillel Retweeted Hillel

          Also a lot of Fermi Estimate questions about domains are also brokenhttps://twitter.com/hillelogram/status/1145135796464357377 …

          Hillel added,

          Hillel @hillelogram
          Okay, here's a much more serious problem: "1 in 20 households have a regularly-tuned piano" is a _severe_ overestimate. 1. The only estimates I could find suggest that only 1 in 20 Americans know how to play piano, period. Not every single one will have their own piano.
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        2. Jesse Myers‏ @jbmsf May 26
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          Replying to @danluu

          I'd love to get your answers 1-N. In the past, I've tried to make "design" problems that omit key details so that a "right" answer must ask for more information and challenge the problem. No idea if it works, but I'd like to think that your answers are a core part of design.

          1 reply 0 retweets 0 likes
        3. 「sharpobject」‏ @_sharpobject_ May 26
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          Replying to @jbmsf @danluu

          I think problems that omit key details may be tough to communicate well to other interviewers. Occasionally I end up in exchanges like "So you're asking me how this service should handle the situation where this service is not working?" "Yes."

          2 replies 0 retweets 0 likes
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        1. brian‏ @misterbwong May 26
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          Replying to @danluu

          Agree with this but isn’t the real problem the fact that they threw out answers 1-4 not that they asked the wrong question? Build vs buy is a real thing and ignoring it makes the question leading and contrived.

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        2. Kevin Cantú‏ @killerswan May 26
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          Replying to @danluu

          I do think it’s essential to have a discussion like the one you describe (your 1-4, too) where collectively you exercise listening and high-level technical communication to scope something out at some appropriate level of interesting conversation

          1 reply 0 retweets 0 likes
        3. Kevin Cantú‏ @killerswan May 26
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          Replying to @killerswan @danluu

          it’s hard to deal with an engineer who failed such a test eager to bring on this new open source solution and that vendor and this thing — and more credentialed than most of the team — but totally unable to get down to brass tacks and describe something fully or ship it

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        1. Kornilios Kourtis‏ @kkourt May 27
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          Replying to @danluu

          For me, there is little association between design interviews and actual design. The goal of the interview is establishing expertise. I wouldn't approach design interviews the same way as I approach design, and vice versa. (Ditto for programming.)

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