Consistent Hashing and why it might not be the correct answer to your system design interview

I’ve conducted many system design interviews in the past. Whenever I brought up the topic of database sharding, the candidates almost always shout out “Yes, yes I know! Consistent hashing!”. If you probe them further, they will draw this classic ring diagram on the whiteboard.

WikiLinuz, CC BY-SA 4.0, via Wikimedia Commons

But if you have read Martin Kleppmann’s great book Designing Data-Intensive Applications, you might notice a sidenote:

…, this particular approach (Consistent hashing, as defined by Karger et al.) actually doesn’t work very well for databases, so it’s rarely used in practice (the documentation of some databases still refers to consistent hashing, but it is often inaccurate).

Then why is every system design interview study guide tell you otherwise? Let’s dive into this topic in this post.

Generating a notification sound in command-line

You want to play a notification sound in a Linux shell script, but don’t want to download any sound files (e.g. MP3, WAV, MIDI). Here is a script that generates the sound on-the-fly:

First install SoX, the Swiss Army knife of sound processing programs.

sudo apt-get install sox

Then:

play -n synth 0.3 pluck A3 vol -20dB repeat 2

• play: the player command from SoX.
• -n: Play a “null file”.
• synth 0.3 pluck A3: Play the A3 (220.00 Hz) sound for 0.3 seconds, with a waveform that simulates a guitar string pluck.
• vol -20dB: The default is too loud, reduce the volume by -20dB.
• repeat 2: Repeat twice (i.e., total 3 times).

How to import serde's custom derive macors properly?

TL;DR Follow the official documentation

Caveats in Terraforming WAF V2 for CloudFront

If you want to add a WAF V2 (aws_wafv2_web_acl) to a CloudFront distribution (aws_cloudfront_distribution) using Terraform, there are a few caveats:

Check MongoDB index usage statistics

Run this command to get the usage of each index: