I want to learn how lexers, parsers, interpreters are built. I also want to learn about how DBs work under the hood. The best way to learn about both? Build your own DB with custom SQL-like query language.

Also, some good blog posts will come out of this, hopefully.

Language topics:

• backtracking parsers
• symbol tables
• AST visitor interpreters
• stack or register based VMs
  • memory allocation and deallocation

DB topics:

• file systems
• fast data fetching (b-trees)
• I don't know anything about this section, that's the point

There's enough work for 5-10 years here.