BitMask Fields

This blog post is in response to one of the questions that we got from our reader. Here is the question:

“I’d like to hear your opinions on bitmask fields. I have found a lot of flames on using bitmask fields into RDBMS and most of them look a lot like the cons of EAV models, which I do agree (I just learned it the hard way, after using this design in a system which later became real hell), but what are the cons in bitmask fields when we just need an “open” set of boolean flags? Apart from indexing (which I believe would be impossible to be done) would it be better to add a new bit field for every new flag to your existing databases than using a bitmask field?”