from Hacker News

Claim: the ideal PR is 50 lines long

by samscully on 2/7/24, 2:25 PM with 124 comments

• by appplication on 2/7/24, 3:03 PM

  I have found that teams who allow larger PR sizes without complaining about it can get a lot done a lot faster. Which is to say having 50 line PRs are not ubiquitously ideal, but are somewhere on the spectrum of acceptable but come with definitive tradeoffs. Reviewing and merging 10x60 line PRs is, in my experience, more time intensive than reviewing one 600 line PR.

  Most of the tests for and new functionality alone in any of our PRs well exceed 50 lines. Indeed we have 2-3x more test code than actual code. So should we be writing less tests? Merging the code first and later the tests? Merging the broken, codeless tests first and then the code?

  It’s all ridiculous. Just make PRs that represent unit change, whatever the means to you. The unit functionality is independent of lines of code. Sometimes that is 12 lines, sometimes it’s 800. Yeah large PRs are harder to understand but that’s why you have tests. Also XXL PRs aren’t usually happening every day. If they are, you have a very productive team and maybe you should count yourself lucky.

• by hugocbp on 2/7/24, 7:54 PM

  I'm probably in the minority here, but personally I'd much rather review a 300 line PR instead of 6 50-line ones if the change is a single context.

  I briefly worked with a hard line-count-limit for PRs and I thought it made everything much worse. It is fine for changes that are actually small, but when you need to go back and re-open 4, 5 merged PRs in different tabs to get the full context again, the time to review increases tenfold with tiny PRs that don't really make complete sense by themselves.

  I have worked with co-workers that have the complete opposite preference, though, and anything over a set amount of lines wouldn't even be reviewed.

  Interesting to see the numbers on the article, however. My anecdotal experience would make me guess the opposite. I feel like work slows to a crawl once the PRs are artificially limited and broekn up like that, specially in fast moving companies and startups.

• by ysavir on 2/7/24, 3:27 PM

  How reliable is reversion as a metric? In my experience, the problem with 50 line PRs (that aren't just making a quick adjustment to something, but actually trying to build new functionality in sets of 50 line PRs) is that each change is so isolated, that when everything has to be combined into an actual working feature, the small changes aren't coordinated with each other. The PR that adds the DB migration doesn't add the appropriate columns needed to actually store the information sent from the frontend, etc. All the small things that can't be planned for in advance and are only discovered during implementation.

  Those small PRs might not be reverted, but there are probably a fair number of 50 line PR follow ups that end up modifying the original implementation, and using up more total time and effort than if it was just a larger PR implementing the feature in its entirety.

  I wonder how many of the large PRs they say take longer to merge and get less comments are actually feature branches into which the smaller PRs are merged, and which we expect to hang open for long periods of time with little interaction.

  This analysis seems to take a set of data without much investigation into what the data actually represents and makes an immense effort to find some conclusions about the context-less data.

• by Zealotux on 2/7/24, 2:59 PM

  I’m reading this article on a break from reviewing a PR with more than 300 lines changed over 20+ files and I wonder if some people simply live in some sort of alternative wonderland universe.

  The “ideals” are almost never a thing I see in my daily job, and I’ve worked for countless companies as a contractor.

• by waffletower on 2/7/24, 4:10 PM

  I file this under the category of "needless rules created without sufficient context". The author's experience is not sufficient to generalize to the diversity of development environments where pull requests are utilized. Hopefully, OP is a good listener and can compromise when their strong opinions meet resistance from other developers at their organization.

• by tcmart14 on 2/7/24, 8:31 PM

  For me personally, it shouldn't be about line count. A PR should have scope of a single feature/piece of functionality. Or if it is a PR for a bug fix, 1 bug fix per PR. If its 1 line, 2 lines, 50 lines, 500 lines, I don't care. Each PR should address one single problem.

• by jitl on 2/7/24, 3:29 PM

  If I need make a new thing - for example, introduce an end-to-end benchmark suite for a service, it may take something like 2000 lines. If I split that up into 50 line PRs, it’s 40 PRs. I’ll also need to write a pre-read document explaining the overall design because PR descriptions for each change individually won’t be enough context for a reviewer to understand.

  If CI takes 15 minutes and I create PRs one by one, I’ll need to wait a total of 10 hours just for CI, which is impossible, I’ll need to use stacked PRs. If I’m using stacked PRs, that means I do all the work up front, and then try to painstakingly split up my final code into little 50 line chunks that build incrementally. I’m sure someone will say “oh just write incremental small commits to begin with”, but that never seems viable to me. Code and design evolve as I build in ways that would make the review of the first 50 lines I commit on the project pointless since none were retained in the final product. So not only do I have to build this feature, and write 40 PR descriptions, and write an overall meta-PR-description for the change in aggregate, I also need to cut my finished code up into puzzle pieces for reviewers to mentally re-assemble.

  Anyways, maybe for maintaining mostly-done features 50 lines is nice, but I’d much rather a new feature or larger change be a handful (1-3) of larger (500-2000 line) PRs possibly accompanied by pair-review/walkthrough discussion.

• by GravityLab on 2/7/24, 9:05 PM

  The correct PR is the one that solves the problem the best. The correct PR's size has nothing to do with the # of lines it is. Tracking time to merge is not that meaningful because merging code does not in itself say anything about the value of that code in production. That is the type of metric that may become a target for a scrum master or project manager despite it being fairly divorced from the reality of moving the right code into the production environment.

• by NickM on 2/7/24, 4:12 PM

  Lots of commenters seem to be arguing against straw men. The article doesn't say "you need to follow this exact rule on all your PRs"; it doesn't frame any of this as a hard limit or a "best practice", it's just saying that small PRs are easier to understand and review. This doesn't seem terribly controversial to me. The fact that the article actually includes data in support of this thesis is icing on the cake.

  Now, yes, it can be a bit more work to split up big PRs into smaller standalone changes that can be merged in isolation, but it seems plausible that the benefits might outweigh the extra work in many cases. The whole idea of a version control system is to create a useful history of changes over time; making each individual changeset simpler and easier to understand seems like an admirable goal.

• by lakpan on 2/7/24, 2:57 PM

  I wish. My small PRs die by a thousand bikesheds. My large refactors are followed by LGTMYOLO

• by distortionfield on 2/7/24, 7:51 PM

  In this thread: software engineers all of a sudden put some value on counting lines of code.

• by TomSwirly on 2/7/24, 2:59 PM

  > 50-line code changes are reviewed and merged ~40% faster than 250-line changes.

  Reviewing a 50-line code change in 60% of the time it takes to review a 250-line code change means the shorter code review takes _four times_ as long to review per line.

• by 3cats-in-a-coat on 2/7/24, 3:30 PM

  Just my comments are 50 lines, but thanks I'll never stop finding these "functions must be this long and classes must have that many properties, and PR should be so many lines" etc. rules hilarious.

  It cheers me up that people so naive exist.

  Size is contextual to the thing the PR regards. Maybe it's one char. Maybe it's 500 lines. Maybe it's 10k lines. Screw this.

• by lightbendover on 2/7/24, 3:43 PM

  If someone sends me an multi-thousand line CR, I'll review it and give them impactful feedback. I may miss some details, but I guarantee I'll miss close to all of the details if that is split over 40 CRs. I wouldn't want to work with someone who has time to review like that unless it's a very niche domain.

• by yurishimo on 2/8/24, 8:24 AM

  We merged a PR a few days ago that was 40,000 lines added and about 13k lines removed. Tbf, there was quite a bit of config and generated code in there, but the actual changes were at least half of that.

  It was tested in smaller chunks in a feature branch, then the larger feature was merged. There was some testing done on the huge feature branch, but not everything that was present in the smaller PRs.

  In our case, this new "feature" was a complete overhaul of our business logic engine. Over time, we had essentially developed 3 or 4 different API versions for various business tasks, with a lot of logic being duplicated between them. We want to bring it all under one umbrella, and after about 8 years, we think that we have a good idea of what sort of abstraction can work for the next 8 years.

  Now that the engine is merged, we need to start the grueling task of actually moving logic from the old APIs into it and removing them from our codebase. We spent about 6 months (between 2 devs) writing the engine and I suspect it will take 2 years to move all of the logic into the new engine.

  Idk where I was going with this comment anymore, but needless to say, I don't often see 50 line PRs at work!

• by binsquare on 2/7/24, 8:49 PM

  This is one of those cases of where we're focusing on the wrong metric for a very generic problem.

  There's too many facets to what makes a PR good that boiling it down to line count is silly.

  Ex. Small code changes are required if the solution requires it - forcing 5 lines change to 50 lines would be considered wildly bad idea. On the other hand a 500 line PR to solve one problem suddenly broken down to 10 PRs makes the review far harder depending on the context.

• by the1024 on 2/8/24, 12:19 AM

  We went through a relatively controversial process w.r.t. enforcing this at my last co. What it really came down to was intent vs. impact - the intent of the change was to enforce better development practices, especially across junior engineers that had shipped monster prs containing multiple bugs that were extremely hard to catch ("the easiest way to ship a one line change is in a thousand line pr").

  This worked reasonably well in terms of forcing junior engineers to reason harder about what an atomic change should look like, but also impacted senior folk that were making atomic changes that encompassed broad areas of the codebase. We eventually reverted the change and relied on implementing CODEOWNERs to enforce senior devs to request changes when PRs got out of hand.

  There's definitely nuance to enforcement of best practices across an entire organization; haven't really seen it done well although I've primarily worked at startups.

• by bvrmn on 2/7/24, 11:08 PM

  PR line count is such a silly metric. For example my recent PR +600/-900 lines. What you can deduct from that? Is it complex?

  Changes were quite simple. 600 common lines are about rearranging big module into multiple smaller modules. 300 removed lines are technically could be in a separate PR, but it's some cleanup aftermath related to rearrangement.

• by SAI_Peregrinus on 2/8/24, 3:56 AM

  If you change enough at once GitHub gives up and displays "infinity files changed". Likewise for lines. I've gotten such a PR merged in a finite amount of time. Thus, by GitHub math, infinitely large PRs merge faster per line changed than any other size.

• by Draiken on 2/7/24, 4:07 PM

  What a weird claim.

  PRs that are <50 lines are more often than not documentation, typos and small fixes in my experience.

  Most real value add PRs end up bigger due to tests, documentation changes, and the actual change.

  This for me is the typical claim that'll become an example of Goodhart's law when implemented. Random people that are not engineers will use this to claim "your PR should be 50 lines long" as some sort of absolute truth, when in reality the number of lines of code is absolutely irrelevant most of the time.

  Context and details matter. Sometimes multiple small PRs are better. Sometimes a larger PR is better. It always depends. These absolutist claims that "this is better" is what leads to atrocious management practices that always end up getting summarized to a number, losing all of its meaning in the process.

  Had we not we moved on from the lines of code metrics already decades ago? :facepalm:

• by karmakaze on 2/7/24, 5:35 PM

  Large and small PRs aren't the only options.

  For a large PR, I usually regroup my changes into smaller unit commits which can be reviewed commit by commit.

  For an even larger (or more complex) PR, I'll make a set of stacked PRs which can be reviewed in pieces, each with a good description of what/why/how stuff is happening in that piece. Once all PRs have been approved, the lot of them can be deployed together.

  I've at times had 3 PRs for a total of 3 line changes, because they were for a single table's schema migration picking new indexes and each had many factors to consider. The PR descriptions were of course much longer.

• by abroadwin on 2/7/24, 7:55 PM

  ITT: company that sells product for breaking PR into smaller PRs claims smaller PRs are better.

  Not saying the claim is necessarily wrong, but it's also exactly what I'd expect given the source.

• by da39a3ee on 2/8/24, 12:20 AM

  This all depends on whether you believe in merging unfinished work to master, or whether you believe features should be completed and tested before merging. Personally I'm in the latter camp, but some of the big tech companies seem to have a style of merging commits representing partial progress toward a feature.

• by avgcorrection on 2/7/24, 3:31 PM

  I personally mostly care about changes per commit. But Bitbucket is terrible about showing commit context to reviewers. And apparently GitHub is not any better.

  Showing some context per commit makes all the difference when I decide to do a first commit which fixes all formatting in the file that I’m visiting (for the real/substantive change).

• by tyleo on 2/7/24, 8:58 PM

  I'm seeing some pretty surprising claims in this thread about, "I prefer reviewing larger PRs," and, "Teams that make larger PRs go more quickly." That all seems like rubbish to me. I've seen data indicating smaller PRs having lower error rates and such and then we have this article with data recommending a 50 line PR size. I've *never* seen data show large PRs are better except for some developers saying, "I prefer it that way."

  Anyways, I don't so much care about the size of a PR as much as I care about how understandable it is. That generally ends up being a few rules of thumb like:

  1. If you change a common function name, change it everywhere but please don't do anything else in the same commit.

  2. If you need to make a change in code you are depending on to accomplish a goal in your own code, try to break the change to the dependency into another commit. There is a little bit of an art here to both understand how to break things up and to not break them up too small.

  3. Try to make your history meaningful rather than just having a bunch of random commits like "fix", "forgotten file", etc.

• by detinho on 2/7/24, 4:37 PM

  I always try to care about the reviewers. Not too large PRs so they don't LGTM it instantly. Not too small PRs so they don't have to switch contexts multiple times a day or search through many smaller PRs to get context why new PR changes specific lines.

• by sithlord on 2/7/24, 4:28 PM

  sounds like the ideal PR includes no testing

• by zer8k on 2/7/24, 3:27 PM

  This has never, and probably never will, be anything more than a theory. In my experience this is only true if:

  1. The "unit of work" is small enough to decompose into a 50 line PR. This is possible on larger codebases and less verbose languages. It can enforce over-DRY code which often leads to a lower universal ability to understand what is going on.

  2. The team responsible for reviewing is responsive. I have never worked at a company where PR reviews happened quickly. Everyone is busy, everyone is overworked, and often times PRs are a chore that can be put off until later. Of course you can make some labyrinthine chain of small PRs all merging into one big PR but the problem still exists. I'd personally rather review a 300 line complete PR written well than 6 PRs that I have to constantly recall context on.

  This advice follows the same logic as the asinine cyclomatic complexity rules. Yes, in theory they are sound. In practice, it's more of a flexible benchmark rather than a hard rule. But since someone inevitably writes YASL (yet another stupid linter) that enforces these types of things, an enterprising work-focused engineer will end up spending either more time fixing code to please the linter or more time exploiting loopholes in the rules.

  Just write Good Code (TM) - whatever that looks like.

• by awestroke on 2/7/24, 2:45 PM

  Forget about refactoring then

• by charcircuit on 2/7/24, 3:35 PM

  So if we fix a > that should have been >= we should add 49 lines of comments explaining this? Or perhaps the PR is doomed to never be ideal due to being short.

• by Miraltar on 2/7/24, 4:06 PM

  I think this might just highlight how simple changes are indeed simpler instead of showing that slicing one big PR into severall smaller ones is actually good.

• by mirekrusin on 2/7/24, 4:10 PM

  Making pasta is easy. Eat pasta 3 times a day, every day.

• by hyggetrold on 2/7/24, 10:11 PM

  Counterclaim: the ideal PR is the one that's never opened. Instead, have high test coverage and do trunk based development.

• by wredue on 2/7/24, 8:42 PM

  Claim: the ideal PR is exactly as long as it needs to be to achieve its goal.

  The same goes for functions

  Please stop listening to this garbage advice.

• by sebastianconcpt on 2/7/24, 4:13 PM

  Still valid disregarding the verbosity or lack of the computer language of that PR? Where is the proof of that?

• by User23 on 2/7/24, 7:20 PM

  This is a fine example of how misguided measuring for the sake of measuring really is.

• by xkcd-sucks on 2/7/24, 7:08 PM

  > If what you care about is maximizing the amount of engagement and feedback on your code over the long run, you’re best off writing as small of PRs as possible.

  > The highest volume coders and repositories have a median change size of only 40-80 lines.

  This claim is rational under the Facebook axioms, so to speak.

• by siva7 on 2/7/24, 9:12 PM

  It's times like these when i question the quality of HN or how can such shit get so many upvotes?

  > We flew down weekly to meet with IBM, but they thought the way to measure software was the amount of code we wrote, when really the better the software, the fewer lines of code.” — Bill Gates

• by agilob on 2/7/24, 4:25 PM

  Your ideal PR has no tests?

• by nhggfu on 2/7/24, 3:37 PM

  OP needs to discover the <acronym> html tag or define their acronyms imo. i thought they were talking about press releases. sheesh

• by stratigos on 2/7/24, 3:58 PM

  The response to seeing 10k lines of code in a PR is not to skim it, that is harming one's company. The response is to request the author to justify its size, and/or reject the PR and request that it be delivered in smaller sizes. If the author cannot, then the author needs their responsibilities reduced and to receive additional mentorship.

  Skimming a PR is pure cognitive dissonance, dont do this and complain when your app turns into a dumpster fire.

• by oglop on 2/8/24, 8:03 AM

  I would kill myself if I worked somewhere where they actually did this type of analysis. I cannot wait for AI to replace me and I become homeless but free from a horrible choice to get involved with computers many years ago. Damning me to these type of just asinine bullshit conversations and posts. I wish I had made different choices.

• by progrus on 2/7/24, 7:42 PM

  Agrees with gut check.

• by armatav on 2/7/24, 8:52 PM

  Just use your brain to PR a feature or some sub-piece of a feature instead of this arbitrary shit.

  Who wants to spend hours bothering with hardline process - you’re the programmer, you’re going to be the guy answering any questions on your pull; therefore you’re going to have to look at it yourself.

• by pestatije on 2/7/24, 4:59 PM

  PR - pull request

• by svaha1728 on 2/7/24, 7:19 PM

  These types of arbitrary rules are why projects end up depending on deprecated packages. Nobody can do it so everyone whistles around a slowly smoldering dumpster fire.

• by tehnub on 2/7/24, 8:58 PM

  Correlation is not causation. What if changes that are inherently more complex — which take longer to review, are more likely to have bugs, etc — typically require 250 lines or more?

• by physicsguy on 2/7/24, 2:48 PM

  ... or is constrained to doing a single logical thing (perhaps many times).

• by LudwigNagasena on 2/8/24, 12:19 AM

  Typical rookie stats mistake of confusing correlation with causation.