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
New
This article was written by @rvirding …over a decade ago! Posting here in case anyone else finds it of interest and adding it to our Erla...
New
It’s easy to view yourself as “not a real programmer.” There are programs out there that everyone uses, and it’s easy to put their develo...
New
Following up on the previous post on using UDP multicasting to broadcast and detect peers on a network, I create a registry of those peer...
New
This post is a spiritual successor to Loris Cro’s Go cross-compilation.
The encounter
During a recent stage 2 meeting Jakub Konka wanted...
New
I’ve been more serious about learning Rust recently, after dragging on with passive learning for a while. My first real programming langu...
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
Tej Pochiraju joins the mix to discuss Progressive Web Apps and how you can support them using Elixir and Phoenix to control IoT devices....
New
In episode 78 of Thinking Elixir, we talk with Chase Granberry about Logflare. We learn why Chase started the company, what Logflare does...
New
Ruby’s Struct is one of several powerful core classes which is often overlooked and under utilized compared to the more popular Hash clas...
New
Other popular topics
Hello Devtalk World!
Please let us know a little about who you are and where you’re from :nerd_face:
New
Ruby, Io, Prolog, Scala, Erlang, Clojure, Haskell. With Seven Languages in Seven Weeks, by Bruce A. Tate, you’ll go beyond the syntax—and...
New
New
Hello everyone! This thread is to tell you about what authors from The Pragmatic Bookshelf are writing on Medium.
New
Create efficient, elegant software tests in pytest, Python's most powerful testing framework.
Brian Okken @brianokken
Edited by Kat...
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
I am trying to crate a game for the Nintendo switch, I wanted to use Java as I am comfortable with that programming language. Can you use...
New
Author Spotlight
Erin Dees
@undees
Welcome to our new author spotlight! We had the pleasure of chatting with Erin Dees, co-author of ...
New
Inside our android webview app, we are trying to paste the copied content from another app eg (notes) using navigator.clipboard.readtext ...
New
Programming Ruby is the most complete book on Ruby, covering both the language itself and the standard library as well as commonly used t...
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /wasm
- /ruby
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /emacs
- /haskell
- /java
- /svelte
- /onivim
- /typescript
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /flutter
- /elm
- /vscode
- /ash
- /html
- /opensuse
- /zig
- /centos
- /deepseek
- /php
- /scala
- /react-native
- /lisp
- /textmate
- /sublime-text
- /nixos
- /debian
- /agda
- /django
- /kubuntu
- /deno
- /arch-linux
- /nodejs
- /ubuntu
- /revery
- /manjaro
- /spring
- /lua
- /diversity
- /julia
- /markdown
- /slackware








