Worked at a company which did nightly data imports. Things worked until 'companyx' became a cEient, and the imports were huge. They would take 18-20 hours. Then longer. eventually they were touching the 24 hour mark - unacceptable. Client's data would be more than a day behind. Granted it was a moderate amount of data, but shouldn't take that long.
I was 'new' there - only started a month before - and the rest of the team who'd put this together had been there a year or more. I reviewed what was in place, took a couple of days, and got it down to an hour. Then worked with the existing team and we got it down to under 30 minutes with some tweaking.
I do see some eyes rolling when I tell that, as I know it can sound terribly self-aggrandizing. However, I had a decade of experience at this point, and the rest of the team was just out of college; they'd never faced this problem before. I basically just took the data and imported in small chunks in to in-memory tables (to avoid hitting the disk), and copied those to disk every X rows, and dropped indexes until everything was done. It wasn't rocket science, but did take someone who had a deeper understanding of DB mechanics.
As I'm telling this, I always realize they have no way of verifying this, and essentially I'm just another bullshitter. The more believable I sound, there's an equally high chance I'm either really good, or just a really good bullshitter, and nearly every time, the person I'm talking to has no idea how to tell the difference. It's worse as you get older, because the younger folks just think you're waxing nostaligic about the 'good old days'.
You can't just say "I did X in Y by using Z": you need to begin by explaining that once upon a time there used to be a thing called Y, and on that thing it used to be very hard to achieve X, but in those ancient days there was also a tool called Z, etc.
CBI is a fairly effective technique for general interviewing, because you uncover how people actually behave rather than how they like to think they behave. Most of the gold is in the follow up digging questions, which should separate the bullshit answer from a real one.