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stettix / things-i-believe.md
Last active April 18, 2026 10:27
Things I believe

Things I believe

This is a collection of the things I believe about software development. I have worked for years building backend and data processing systems, so read the below within that context.

Agree? Disagree? Feel free to let me know at @JanStette.

Fundamentals

Keep it simple, stupid. You ain't gonna need it.

Quick Tips for Fast Code on the JVM

I was talking to a coworker recently about general techniques that almost always form the core of any effort to write very fast, down-to-the-metal hot path code on the JVM, and they pointed out that there really isn't a particularly good place to go for this information. It occurred to me that, really, I had more or less picked up all of it by word of mouth and experience, and there just aren't any good reference sources on the topic. So… here's my word of mouth.

This is by no means a comprehensive gist. It's also important to understand that the techniques that I outline in here are not 100% absolute either. Performance on the JVM is an incredibly complicated subject, and while there are rules that almost always hold true, the "almost" remains very salient. Also, for many or even most applications, there will be other techniques that I'm not mentioning which will have a greater impact. JMH, Java Flight Recorder, and a good profiler are your very best friend! Mea

Thread Pools

Thread pools on the JVM should usually be divided into the following three categories:

  1. CPU-bound
  2. Blocking IO
  3. Non-blocking IO polling

Each of these categories has a different optimal configuration and usage pattern.

@SystemFw
SystemFw / Free conversation.md
Last active October 17, 2023 09:57
Explaining some of the mechanics of interpretation of Free programs

Balaji Sivaraman @balajisivaraman_twitter

Hi all, I need some help understanding a piece of Doobie code from the examples. It is the StreamingCopy one: (https://github.com/tpolecat/doobie/blob/series/0.4.x/yax/example/src/main/scala/example/StreamingCopy.scala). I am using a modified version of the fuseMap2 example from that file. Here’s how I’ve modified it for my requirements:

  def fuseMap[F[_]: Catchable: Monad, A, B](
      source: Process[ConnectionIO, A],
      sink: Vector[A] => ConnectionIO[B],
      delete: ConnectionIO[Unit]
  )(
 sourceXA: Transactor[F],