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
Greetings from Membrane Framework team!
Check out our case study based on our latest projects at Software Mansion.
https://blog.swmansi...
New
Is Zig the Long Awaited C Replacement.
Comparison with previous C contenders such as C++, D, Java, C#, Go, Rust and Swift
https://erik...
New
I had a bit of a mini-adventure following Sobelow’s advice on adding a CSP to a Phoenix App. If you want to follow along, or want to add ...
New
Summary: I describe a simple interview problem (counting frequencies of unique words), solve it in various languages, and compare perform...
New
The perspective of an ignorant computer science undergrad
It’s likely that you read the title of this post and thought “what is this guy ...
New
I discovered Elixir and Go at about the same time (2019). I had pivoted almost eight years of working as a Java developer, and part of me...
New
This thread was posted by one of our members via one of our news source trackers.
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
I describe how we use Hot Reloading with Webpack to develop faster and show how to integrate Webpack 5, webpack-dev-server, and Phoenix f...
New
Other popular topics
Learn from the award-winning programming series that inspired the Elixir language, and go on a step-by-step journey through the most impo...
New
No chair. I have a standing desk.
This post was split into a dedicated thread from our thread about chairs :slight_smile:
New
I know that -t flag is used along with -i flag for getting an interactive shell. But I cannot digest what the man page for docker run com...
New
Small essay with thoughts on macOS vs. Linux:
I know @Exadra37 is just waiting around the corner to scream at me “I TOLD YOU SO!!!” but I...
New
Create efficient, elegant software tests in pytest, Python's most powerful testing framework.
Brian Okken @brianokken
Edited by Kat...
New
Author Spotlight
Dmitry Zinoviev
@aqsaqal
Today we’re putting our spotlight on Dmitry Zinoviev, author of Data Science Essentials in ...
New
Was just curious to see if any were around, found this one:
I got 51/100:
Not sure if it was meant to buy I am sure at times the b...
New
If you want a quick and easy way to block any website on your Mac using Little Snitch simply…
File > New Rule:
And select Deny, O...
New
zig/http.zig at 7cf2cbb33ef34c1d211135f56d30fe23b6cacd42 · ziglang/zig.
General-purpose programming language and toolchain for maintaini...
New
Author Spotlight:
Bruce Tate
@redrapids
Programming languages always emerge out of need, and if that’s not always true, they’re defin...
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /wasm
- /ruby
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /java
- /emacs
- /haskell
- /svelte
- /onivim
- /typescript
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /elm
- /flutter
- /vscode
- /ash
- /html
- /opensuse
- /zig
- /deepseek
- /centos
- /php
- /scala
- /react-native
- /lisp
- /sublime-text
- /textmate
- /nixos
- /debian
- /agda
- /django
- /deno
- /kubuntu
- /arch-linux
- /nodejs
- /revery
- /ubuntu
- /manjaro
- /spring
- /julia
- /lua
- /diversity
- /markdown
- /v









