[johnnygood]

So, I encounter a lot of programmers that have read a little and consider themselves to really know what they're talking about. However, they can't explain how an index works - not even in simple terms. Like, if I'm looking for someone with the username 'johnnygood', why would indexing the username column make that lookup faster? Even a very simplistic answer like, "an index orders the information so that the database server can jump to that record binary-search style rather than looking through every row" would be wonderful.

In that light, I think that programmers should know the basics of computer science: what references are; how a linked list works; a little about tree data structures; stacks, queues; basic sorting and searching stuff; etc. I'm not saying that you need to be able to talk about everything off the top of your head. I just think a familiarity with the theoretical concepts is good.

On the other end, I see a lot of people who know that PHP interprets strings using single quotes faster than double quotes, but have no idea why NoSQL might scale better (and might actively think it's because of the SQL language).

I want someone to say "a lot of the NoSQL technologies work by having you pre-compute data so that your data structures have the information you want to display together stored together in a structure that can be read more quickly like a hash." It isn't magic.

[mixmax]

I somewhat disagree with this - it depends entirely on what you're doing. If you're writing a 3D gaming engine you're absolutely right, but if you're writing simple webapps, which most people are nowadays, you don't really need to know what a linked list is. Your programming language of choice will abstract it away.

These are certainly good things to know, but for most people not really essential or even important.

[tbrownaw]

if you're writing simple webapps, which most people are nowadays, you don't really need to know what a linked list is. Your programming language of choice will abstract it away.

You still need to understand it at least well enough to know that you really shouldn't try to access random list elements. Just like you need to understand arrays well enough to not try to insert things into the middle of them.

[rikthevik]

I think Yegge was right about compilers. Without understanding low-level languages and how high-level languages get transformed, a programmer can never really understand the language he's working with.