About

This is my solution to the Redis Server coding challenge by John Crickett.

It is writen in C++23 using Clang and libstdc++ on Ubuntu. Due to some issues when using Asio with modules on msvc, I have not yet been able to make it compile on Windows, unfortunately. This is also the first time I build something more than a test program that uses modules.

State

The challenge is almost done, except for the extra commands in the second to last step. The code is a mess, but it runs well:

The following command

redis-benchmark -q -t SET,GET -k 1 -d 512 -n 100000 -c 50 -r 1000000

This server produces the following benchmark results:

SET: 49726.51 requests per second, p50=0.503 msec                   
GET: 46533.27 requests per second, p50=0.535 msec

Which is very similar to the 'real' redis server installed via apt-get on my computer:

SET: 50377.83 requests per second, p50=0.495 msec                   
GET: 47460.84 requests per second, p50=0.519 msec

TODO

Things that could (should) be improved if this was a real production application:

• Heavily refactor the RESP parser - currently it attempts to rely on the buffer allocated by the connection handler to avoid any allocations for as long as possible. Just before storing data in the database, it is "materialized" and storage for the entry is allocated. This works, but led to code duplication that should be refactored.

• Add support for varying request sizes in the buffer pool - for the challenge requests are assumed to be 1 kiB or less. In a real redis application requests can of course be much larger than that. The connection would need to check if there is still data in the buffer after reading a request, and if so allocate a larger buffer. Another approach would be to parse the RESP commands using a parser that can work incrementally.

• Currently, all data is stored as string in the database - not sure if this is a good idea or not.

• Add more tests! Unit tests and integration tests. Integration tests an be constructed using redis-cli. Stress tests could be constructed using redis-benchmark. All we need to make that work in a CI/CD pipeline is bash :)

Learning Outcomes

• Working with modules
• Technical tradeoffs (e.g., use multi- or single threading)
• Tradeoffs in project management (what to work on and what not to work on given the limited time of a side project)
• Combat scope creep

Disclaimer

Naming is hard. Despite the name of this project, I am not in any way affiliated with Redis. If you are affiliated with Redis and you think the name of this project needs to change, please contact me and I will make the change.

Requirements

The code has been verified to work with clang-19 on Ubuntu (24.04). On Windows there are compilation errors that are similar to this report. The ticket is still "under consideration" after almost three years, so it's anyone's guess when it can be resolved. If you know a workaround to this on Windows, PRs are always welcome :)

Running

  ./redis-server

To see available arguments, run

  ./redis-server -h

Dependencies

This project stands on the shoulders of the following giants:

• Asio: The stand-alone version of the popular networking library
• CLI11: A command line parsing library