What's better/faster? MySql or FileSystem? Let's imagine a web site that is a directory of people. For each person there may be a profile photo and a biography.

I'll admit my SQL queries could be better but in general what would be faster and use less processing power.

To check if a file exists and then open it
 or

check against MySql to see if a bio exists and display it.

I'm pretty sure in the above case the filesystem will smoke the mysql database.

What if I make the database a read only delimited txt file?

What's faster in this case?

Is there a certain point where if the txt file has too many records it's better to use MySql?
The file system is useful if you are looking for a particular file, as operating systems maintain a sort of index. However, the contents of a txt file won't be indexed, which is one of the main advantages of a database. Another is understanding the relational model, so that data doesn't need to be repeated over and over. Another is understanding types. If you have a txt file, you'll need to parse numbers, dates, etc.

So - the file system might work for you in some cases, but certainly not all.