Ask HN: How to be productive with big existing code base

I think it's always important to lead with an attitude of service and compassion for the labor of others before you and yourself now. Get upside down on that and it makes it really hard to be impactful.

It's easy to get mad at code when you first show up and just apply Chesterton's Fence and move forward. Personally, with legacy systems (and what isn't really?) when I show up to a new project I do my best to grok the internal knowledge and test it. With official tests but also building out an environment around it so I can test conclusions. I document what people tell me, what docs and scripts they link me to, and what my results are. Almost without fail, the institutional knowledge is cargo cult.

People rarely break out of their mold for what works for the thing they need to work on. This isn't a problem that they need to fix, but legacy systems always need someone to take the time to make more clarity. So as a new person I focus on building up dev and deploy environment from zero, over and over. It's kind of an ops process. For me it's about finding multiple/duplicate configuration points, processes, improving VM or container environments, profiling, making sure that if external services are being leveraged that they can be bootstrapped to local dev or at least faked, and confirm tests harnesses if they exist.

With a "big existing code base" I have found that almost universally, the full stack can't be bootstrapped on the devs computers. They rely on tricks to run parts and cloud services and undocumented scripts. It's never because it's impossible and as a new person, I am uniquely qualified to solve that. Once I have a smooth rebuild process I move inward and refactor for clarity and tests, being careful to not disrupt other people's working strategy.

So in my experience, the first 4 weeks are asking questions and documenting the lies while repeated bootstrap. Second 4 weeks is environment cleanup. After that it's learning the system from the outside in by making the entire environment single command bootstrappable. I keep a daily journal of my experience and try to build out docs/readmes to consolidate and correct the practices that were relayed to me in the first 4 weeks as well as new clean up that I'm working on.

Being a new person on a large legacy code base is powerful. You don't have the entrenched survival problems other people have. Clean up and document to explore and try to be an exponential productivity add while you do it. One of my favorite tricks is "adding" features by removing things that people did not remember they have put into production. At my current job, my first three months was -7000 and +500 lines to our master repo. My negative -7000 was more impactful than some people that pushed 100k+/- in commit. Also I find it's useful to wildly speculate about how things work and be willing to be VERY wrong early and often. People are more likely to tell you about how they think something works when they are correcting you than when you ask directly for help. No clue why that's a thing, but it is.

After you get done cleaning things up you can make your own horrible lore and mistakes and start the process all over!

Sometimes the initial design truly was a mistake.

I'd also add here that hindsight is 20/20. You don't really know what you're creating until it's created. Do it again a second time when you know exactly what you're getting at the end, alongside the challenges you'll face in the process of such, and you'd be able to do it faster, cleaner, and just overall better.

First, get your tooling set up, especially a code search tool with go-to-definition and find references. A good code search tool will make you much faster and better at understanding code, finding correct usages, debugging problems, etc.

It also makes it easy to get a URL to any line/region in a code file to paste into email/Slack to ask/answer questions. (Of course, GitHub has URLs, too, but you probably aren't browsing code on GitHub already because it lacks code navigation/intelligence features, so getting the GitHub URL would add an extra clunky step.)

Here is a study of Google's internal code search tool with some example use cases and interesting stats: https://research.google.com/pubs/archive/43835.pdf. Most(?) engineers at companies with large codebases use code search frequently if they've ever tried a good code search tool (i.e., it's hard to give it up once you've used it).

(Disclaimer: I work on a tool that does this, but I'm omitting the name/URL because the advice is general.)

The point is "doing better" is pointless unless it serves a specific business value. Beauty is not a sufficient reason to refactor a code base in production - because refactor always has risks, and those risks should be offset always by some tangible expected reward.