# Valentyn Kit

> I build the Rust core of a self-custody wallet and rebuild the layer underneath from scratch — databases, TCP servers, storage engines — to understand how the real ones work. This is where I write it down.

Distributed-systems and platform engineer. I lead the Rust core of a
self-custody wallet that moves money for 200,000 people, and on nights and
weekends I rebuild the layer underneath from scratch (a database, a TCP
server, a Solana indexer) to learn how the real ones work. The writing is
first-principles and no-hype: one level below and one level above.

## Writing
- [What Linux actually does when you read a file](https://valentynkit.com/blog/what-linux-actually-does-when-you-read-a-file/): I asked for one 4 KiB page and got four back. The same read one page over gave me one.
- [You don't understand a system until you've rebuilt it](https://valentynkit.com/blog/you-dont-understand-a-system-until-youve-rebuilt-it/): Using a system teaches its interface and reading its source teaches its mechanics, but only rebuilding a worse version teaches the constraints, which is where understanding actually lives. Why reconstruction works, and how to build a toy that teaches you something instead of lying to you.
- [Rust's compile errors are other languages' production bugs](https://valentynkit.com/blog/rust-compile-errors-are-production-bugs/): Four Rust compiler refusals, each traced to the silent bug it prevents in Python, JavaScript, or C: float sorting, string indexing, integer overflow, lazy iterators. Plus the one place Rust stays quiet.
- [From one blocking accept() to epoll: a C TCP server up the I/O ladder, measured](https://valentynkit.com/blog/from-blocking-accept-to-epoll/): Building a TCP echo server in C seven times, from blocking through select, poll, kqueue, and epoll, with the cost of each wall measured: a 1.5 second stall, a pegged core, the FD_SETSIZE ceiling, and O(ready) dispatch.
- [Framework knowledge evaporates. Low-level knowledge compounds.](https://valentynkit.com/blog/framework-knowledge-evaporates/): I learned async three times before it clicked. Building a TCP echo server from blocking sockets up through kqueue and epoll in C, seven times, is what finally fixed it.

## Pages
- [About](https://valentynkit.com/about/): who I am, the work, and where I am headed.
- [Open source](https://valentynkit.com/open-source/): side projects in C and Rust built from scratch, and merged contributions to rust-lang, Solana/agave, and other upstreams.
- [Experience](https://valentynkit.com/experience/): work history and skills.
- [Library](https://valentynkit.com/library/): books, papers and talks that shaped how I think, with a candid take on each.

## Optional
- [Full text of all essays](https://valentynkit.com/llms-full.txt): every post concatenated as markdown.
- [RSS feed](https://valentynkit.com/rss.xml)