brentjanderson
Zero downtime Postgres upgrades | Knock
We recently performed a zero downtime Postgres upgrade at Knock. This blog post goes into details about the Postgres considerations, although the BEAM & Elixir ecosystem were invaluable in managing the cutover process.
Some Elixir-related bits:
- We used
DynamicSupervisorto start/stop Oban during the cutover. Without going into too much detail, Oban needs aNotifierto coordinate global state, and we rely on the default Postgres notifier (Although there is a new PubSub notifier that we have our eyes on). This Notifier establishes a persistent Postgres connection that is managed outside of your Ecto Repo, and the easiest way to move Oban over to the new instance was to stop and restart it with a new configuration usingDynamicSupervisor - Metaprogramming made it easier to build facade interfaces to our Ecto Repos so that database requests could be routed to the old or new database instance, based on the state of a launch darkly flag. Internally, LD uses ETS and a persistent websocket connection, which helps lookups be fast and up to date. ETS is still not quite fast enough for the volume of DB queries in our system, and so we also used
:persistent_termto set the flag that determined what state we were in during the cutover process. Benchee helped us verify that we weren’t going to have a performance regression. - We looked at Ecto Repo’s
get_dynamic_repofunction, but determined that using a facade was a better fit for our use case. It’s worth knowing what’s available, though, since Ecto comes with a lot of extensibility out of the box. - The concurrency model of the BEAM makes it so much easier to reason about all of the stuff involved in a migration like this. Although you can take a similar approach with most languages, the BEAM didn’t get in the way of reasoning through the specifics of the cutover, especially around how we maintain uptime and data consistency during a cutover like this.
We may do a full post on the BEAM-related details of this upgrade in the future.
Popular Backend topics
Understanding Partial Moves in Rust.
Partial moves are an interesting but often misunderstood feature of Rust. However, with the right ...
New
Django 3.2 is just around the corner and it’s packed with new features. Django versions are usually not that exciting (it’s a good thing!...
New
Post on using UDP multicasting with Elixir to broadcast presence, and listen for peers, on a local network. I have found this approach us...
New
At Grammarly, the foundation of our business, our core grammar engine, is written in Common Lisp. It currently processes more than a thou...
New
Functional programming is an increasing popular programming paradigm with many languages building or already supporting it. Go already su...
New
PHP 8.1 is already taking shape quite well, yet there’s one feature I’d love to see added, that’s still being discussed: multi-line short...
New
We take a deeper dive with Nathan Long into IOLists in Elixir. We cover what they are, how they work, the power they have when concatenat...
New
Louis Pilfold is the creator of the Gleam programming language. He explains what Gleam is and tells us where it came from.
He then dives...
New
When DoorDash approached the limits of what our Django-based monolithic codebase could support, we needed to design a new stack that woul...
New
Episode 244 of Thinking Elixir. News includes the release of Elixir 1.18.2 with various enhancements and bug fixes, a new experimental SQ...
New
Other popular topics
Thanks to @foxtrottwist’s and @Tomas’s posts in this thread: Poll: Which code editor do you use? I bought Onivim! :nerd_face:
https://on...
New
I ended up cancelling my Moonlander order as I think it’s just going to be a bit too bulky for me.
I think the Planck and the Preonic (o...
New
If you are experiencing Rails console using 100% CPU on your dev machine, then updating your development and test gems might fix the issu...
New
The V Programming Language
Simple language for building maintainable programs
V is already mentioned couple of times in the forum, but I...
New
Continuing the discussion from Thinking about learning Crystal, let’s discuss - I was wondering which languages don’t GC - maybe we can c...
New
Think Again 50% Off Sale »
The theme of this sale is new perspectives on familiar topics.
Enter coupon code ThinkAgain2021 at checkout t...
New
Biggest jackpot ever apparently! :upside_down_face:
I don’t (usually) gamble/play the lottery, but working on a program to predict the...
New
A few weeks ago I started using Warp a terminal written in rust. Though in it’s current state of development there are a few caveats (tab...
New
We’ve talked about his book briefly here but it is quickly becoming obsolete - so he’s decided to create a series of 7 podcasts, the firs...
New
Develop, deploy, and debug BEAM applications using BEAMOps: a new paradigm that focuses on scalability, fault tolerance, and owning each ...
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /ruby
- /wasm
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /emacs
- /java
- /haskell
- /svelte
- /onivim
- /typescript
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /elm
- /flutter
- /vscode
- /ash
- /html
- /opensuse
- /zig
- /centos
- /deepseek
- /php
- /scala
- /lisp
- /react-native
- /textmate
- /sublime-text
- /nixos
- /debian
- /agda
- /django
- /kubuntu
- /deno
- /arch-linux
- /nodejs
- /revery
- /ubuntu
- /spring
- /manjaro
- /lua
- /diversity
- /julia
- /markdown
- /c








