Eero Helenius eerohele

PostgreSQL is Enough

See the new site: https://postgresisenough.dev

Thoughts on yada

Frameworks

Let’s define a framework as any library that contains one or more functions that accept callbacks.

Web frameworks are great for beginner developers who need to get stuff done. But they ultimately force you into a corner. In most applications, experienced developers need to retain control. Libraries are better.

Building a blockchain, assisted by Clojure spec

In an effort to gain at least a superficial understanding of the technical implementation of cryptocurrencies, I recently worked my way through "Learn Blockchains by Building One" using Clojure.

This was a good chance to experiment with using spec in new ways. At work, we primarily use spec to validate our global re-frame state and to validate data at system boundaries. For this project, I experimented with using instrumentation much more pervasively than I had done elsewhere.

This is not a guide to spec (there are already many excellent resources for this). Rather, it's an experience report exploring what went well, what is still missing, and quite a few unanswered questions for future research. If you have solutions for any of the problems I've presented, please let me know!

You don't need to know or care about blockchains to understand the code be

Thread Pools

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

CPU-bound
Blocking IO
Non-blocking IO polling

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

About YUV formats

First of all: YUV pixel formats and Recommended 8-Bit YUV Formats for Video Rendering. Chromium's source code contains good documentation about those formats too: chromium/src/media/base/video_types.h and chromium/src/media/base/video_frame.cc (search for RequiresEvenSizeAllocation(), NumPlanes() and those kinds of functions).

YUV?

You can think of an image as a superposition of several planes (or layers in a more natural language). YUV formats have three planes: Y, U, and V.

Y is the luma plane, and can be seen as the image as grayscale. U and V are reffered to as the chroma planes, which are basically the colours. All the YUV formats have these three planes, and differ by the different orderings of them.

	(require '[clojure.core.async :as async]
	'[clojure.core.async.flow :as flow]
	'[clojure.pprint :as pp])

	;; Monitoring function to show the built-in reporting and error handling
	;; This showcases the centralized monitoring capabilities of the flow system
	(defn monitoring [{:keys [report-chan error-chan]}]
	(prn "========= monitoring start")
	(async/thread
	(loop []

	;;=============== play with flow ==============
	(require '[clojure.core.async :as async]
	'[clojure.core.async.flow :as flow]
	'[clojure.pprint :as pp]
	'[clojure.datafy :as d])

	(set! warn-on-reflection true)

	(defn monitoring [{:keys [report-chan error-chan]}]
	(prn "========= monitoring start")

	"Encode and decode integers (such as database identifiers) using Knuth's multiplicative hashing
	algorithm. Based on https://github.com/jenssegers/optimus."

	;; Permission is hereby granted, free of charge, to any person obtaining a copy
	;; of this software and associated documentation files (the "Software"), to deal
	;; in the Software without restriction, including without limitation the rights
	;; to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	;; copies of the Software, and to permit persons to whom the Software is
	;; furnished to do so, subject to the following conditions:
	;;

	;;; Clojure Macro-writing Macros step by step.
	(ns my.macros)
	;; => nil

	;;;;;;;; ns and vars
	ns
	;; => #namespace[my.macros]

	(def x 3)
	;; => #'my.macros/x

	{:paths ["."]
	:deps {clansi/clansi {:mvn/version "1.0.0"}}}