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Jefferson Gonçalves
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Viperlith

🐍⚡🚀 Viperlith: the Hypermedia-Based Monolith for Python built with Datastar

#🐍⚡🚀 Viperlith: the Hypermedia-Based Monolith for Python

Powered by Datastar GIF

#Introduction

A demo application to illustrate how Datastar works.

datastar.js is a lightweight (11kB) hypermedia framework similar to HTMX (but not).

Starcord screenshot

A Discord-like chat sample application is currently implemented with real-time chat rooms, creating/removing channels and setting nicknames.

🔴 Live demo: https://starcord.fastserial.com

#Benchmarks

This benchmark measures requests per second (RPS) under different workloads in the context of a hypermedia application. To serve a read request, the server must issue 3 separate DB queries touching all 4 tables. The queries perform several joins and require at least 500 completely (pseudo-)random pages from the database. This data is then used to render a ~190 kB HTML template (using Jinja), which must then be Brotli-compressed and returned to the client.

#4 GB Dataset

hypermedia_web_server_throughput_4gb

#40 GB Dataset

hypermedia_web_server_throughput_40gb

#Benchmark Results

Ths exact application was also built using FastAPI and Postgres 🐘. Check it out here.

To see all benchmark results or to replicate them yourself, see the benchmark respository.

#The Stack

Viperlith consists of the following components:

  1. Datastar hypermedia framework.
  2. Litestar ASGI framework: Uses up to 10x less memory as compared to FastAPI.
  3. uvicorn: Popular ASGI web server.
  4. MsgSpec: Provides the same validation capabilities as Pydantic while serializing an order of magnitude faster.
  5. SQLite through APSW: Local SQLite offers minimal operational overhead, and when properly tuned, significantly outperforms Postgres & MySQL for most workloads. APSW provides better control, features and error handling compared to Python's builtin sqlite3 module.
  6. Jinja templates: Templating engine used to render HTML templates.
  7. Tailwind CSS: For declarative styling directly inside the markup.
  8. Brotli compression: Used in Litestar's CompressionConfig to minimize bandwidth for streaming HTML over the wire.
  9. spsc-ring-threadsafe: A ring buffer C extension for inter-process communication on shared memory, up to 100x faster than the standard library's multiprocessing.Queue. Used to queue commands to the single-writer process with exclusive write access to SQLite.

#Architecture

#HTML Streaming

Hypermedia-driven applications (HDA), unlike SPA frameworks (e.g. React, Vue, Angular), eliminate state and logic on the client side. Instead, interactive logic is moved to the backend and page updates are streamed to the client as server-rendered templates over a Server-Sent Events stream and morphed into the local DOM. This is a bit like streaming a movie, except the movie is HTML and you receive new content from updates and UI interactions. The client's browser is effectively reduced to a rendering viewport only capable of displaying raw HTML.

See docs/HTML_STREAMING.md for an introduction to the concept of HTML streaming.

Also see: the Tao of Datastar and Datastar: Why another framework?.

#Quick Start

#1. Copy .env.example and name it .env

cp .env.example .env

Generate a SESSION_KEY with openssl rand -hex 16 and change configurations if necessary.

#2: Create directory for database file in /var/lib

sudo mkdir -p /var/lib/viperlith
sudo chown $USER /var/lib/viperlith

#3: (Optional) Enable launch script permissions

sudo chmod +x ./launch.sh

#4: Run the launch script

./launch.sh

This will launch the application in debug mode with hot reload.

Alternatively, it is possible to launch in production mode with multiple workers:

DEBUG=0 ./launch.sh

#Deploy

Before running compose, make sure environment variables such as SESSION_KEY are present in the shell environment by configuring them in CI. These will take precedence before the defaults inside .env.example.

docker compose --env-file .env.example up --build

By default, the application will bind to localhost on 127.0.0.1:8000. The application will only be accessible from the internet if you have a reverse proxy with an appropriate proxy_pass pointed there. If you have a different setup, edit the compose config as needed.

See .gitea/workflows/deploy.yml for an actual CI deploy job example.

#Tuning

#Disable block device readahead

Block device readahead makes it so when any page is read from disk, the next N sectors are also read automatically (256 by default). This triggers excess page faults and can significantly worsen performance for larger-than-RAM databases.

Readahead can be disabled by setting it to zero like so:

sudo blockdev --setra 0 /dev/sda1

Unfortunately, this setting will not persist across reboots. To make the it persist, a series of steps are required:

#1. Check block devices with lsblk:

$ lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sda       8:0    0   75G  0 disk 
|-sda1    8:1    0 74.9G  0 part /
|-sda14   8:14   0    3M  0 part 
`-sda15   8:15   0  124M  0 part /boot/efi

Pick your primary storage disk, in this case sda1.

#2. Create a systemd service to apply the setting at startup

sudo nano /etc/systemd/system/sda1-readahead-disable.service

#3. Paste the configuration (replace sda1 with your block device)

[Unit]
Description=Disable readahead on sda1
Requires=dev-sda1.device
After=dev-sda1.device

[Service]
Type=oneshot
ExecStart=/usr/sbin/blockdev --setra 0 /dev/sda1

[Install]
WantedBy=multi-user.target

Save and quit the file.

#4. Reload and enable the service

sudo systemctl daemon-reload
sudo systemctl enable --now sda1-readahead-disable.service

#5. Verify that readahead is set to zero

sudo blockdev --getra /dev/sda1

You should see:

0

#Credits

Inspired by Anders Murphy's Hyperlith.

Nova versão disponível.