Meta Software Engineer interview questions

I was contacted via email by HR saying that my friend had recommended I be interviewed for a spot at the company. I was pretty surprised by this, but have found that this is how Facebook often goes about doing things. We scheduled an interview for a few days later, which I thought was going to be a technical interview. When I got on the phone with the interview he asked me about what I've been working on recently, and so I got into this whole thing about my research project which I probably took a good 10 - 15 minutes describing. He basically just verbally nodded through the whole thing. He then asked me about what positions I was interested in interviewing for at Facebook. In my push to prepare for what I was expecting to be a technical interview, I somehow neglected to actually figure out what specifically I could work on at Facebook. I mentioned doing something with the large data sets they work on, since my research focused somewhat loosely on large-scale data analysis. Should have prepped for that one, but no problem. He then told me that he'd be happy to set me up for a phone interview with an engineer as soon as possible and I was like "whaa?! I thought you were one!". Not actually, but I did say that I'd be happy to interview with an engineer and so he got that set up for me. I'll come back and post once I've had my *actual* technical interview (instead of just an HR sanity check)

I had 2 telephonic interviews and the questions are below. Recruiters are pretty cool in facebook. 1. General Resume stuff. 2. Merge Sort - Write code for it. Complexity. 3. SQL - self join: Asked me to write a query, don't remember the exact question. 4. Advantage of B Trees - Used in databases for indexing. Adv. Less number of memory lookups because of less hierarchy. Large fanout.