Systems & CLI · Advanced
Build a Database
Build a small relational database with a SQL REPL, a paged storage engine, and a B-tree index that persists rows to disk.
You build a miniature relational database in C, following the architecture of SQLite: a REPL that accepts SQL-like commands, a tokenizer and compiler that turn them into bytecode, a virtual machine that executes them, and a pager that reads and writes fixed-size pages to a file on disk. You implement a B-tree so that rows stay sorted and lookups, inserts, and splits are logarithmic rather than linear scans. It is worth building because databases are usually treated as black boxes, and implementing one teaches you exactly how indexes, on-disk layout, and durability actually work. Understanding pages, cursors, and B-tree node splits is rare, transferable knowledge that pays off whenever you reason about query performance or storage.
What you build
- Interactive REPL with meta-commands and SQL-style statements
- Tokenizer and compiler that produce an internal statement form
- Fixed-size page layout serialized to a database file
- Pager that caches pages and flushes them on commit
- B-tree index supporting ordered insert and search
- Node splitting when a leaf or internal page fills
- Cursors for scanning rows in key order
What it teaches
- B-tree structure, search, and node splitting
- On-disk page layout and serialization
- Pager and buffer-cache design
- REPL parsing and a compile-then-execute pipeline
- Cursors and ordered iteration
- Durability and how databases persist data
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Take it further
- Add a WHERE clause and basic query filtering.
- Support deletes with B-tree node merging or rebalancing.
- Add a write-ahead log for crash recovery.
