Fair point. I was unfamiliar with B-Trees because most of my time is spent as DevOps/Networking/Sysadmin. It took me 15 minutes to learn and understand what they are and how they work.

http://slady.net/java/bt/view.php?w=800&h=600 http://en.wikipedia.org/wiki/B-tree http://en.wikipedia.org/wiki/B%2B_tree http://guide.couchdb.org/draft/btree.html

Now if you make understanding B-trees a prerequisite for the job, I can at least learn it ahead of time for the position.

how often does a normal software developer find himself in a situation where he has to know about B-Trees in depth?

Basic computer science problems creep up often enough (about once a month) at my mostly normal job. We had to implement a prefix trie (specifically a modified radix trie with extra caching) to solve an interesting problem.

If you don't know about these data structures or algorithms, you won't even know where to look.

When he works for the company that this whole conversation is stemming from.

Database indexes are very frequently btrees; understanding how a btree works can inform how you structure and query data, resulting in substantially better software. They're also a generalization of the binary search pattern, which every programmer should be able to describe and utilize.