How would one go about reviewing a piece of code like this?
One of the things I'd typically do is peek at the commit history. Seeing what people worked on and how they did it tends to say a lot about a project. But with LLMs generating 7101 commits in less than a month that isn't feasible. Even looking at a single day is way too much [1]. It probably also doesn't make sense since the commits content won't tell you much anyway.
ps. How do you easily get to the first commit in a repo on GitHub? Browsing commit history feels rather tedious
I start to see a lot of these re-writes that depend on tests to state that its working. But the things that make software like Postgres and SQLite reliable are not mostly the test, but the real world production scars. That's where the reliability comes from, years and years of running in production.
> not mostly the test, but the real world production scars
Most extensive test suites are exactly production scars: every time you have a bug or a regression, you write a test that confirms correct behaviour.
SQLite is a good example to bring up because its extensive closed-source tests are what’s often cited as being what keeps people from forking it. (Turso did it, though, but it takes a company to deliver some guarantee of equivalent diligence.)
Sure, but behaviors that never have a bug or regression don't get a test. Software of this kind of complexity has all kinds of behavior that has never been broken, and doesn't have a specific test written for it.
Getting an extensive test suite passing is certainly orders of magnitude better than having no test suite at all, but it still doesn't tell you as much as you need to know. I would absolutely never trust an LLM Postgres rewrite (in any language) in production based on "only" Postgres's test suite passing.
I've also seen situations where a customer reports a bug, the fix breaks some regression, and the updated behavior to work around the fix breaking the regressions turns into an undocumented feature.
Or even a human rewrite merely because some language is the current fad. A rewrite in a different language should be done for very good reasons, to solve problems that are bigger than the costs of all the bugs that will be introduced.
This feels like the image of the plane that returns from battle with bullet holes, and the engineer being asked to path up where the holes to make it stronger. Only to be told to patch where there weren't holes as those planes didn't make it home.
While not an exact fit of an analogy, those tests patch what was a problem with Postgres in the wild. What it doesn't cover are the things that worked in Postgres without tests, but may fail in port and go undetected.
The maintainers that wrote those tests will have experience you won't get out of a rewrite.
I think this is also where the real work is. A rewrite is one thing, that you can show off with a flashy blogpost. The maintenance, for years to come, won't be of that nature yet it still requires as much work.
> Most extensive test suites are exactly production scars: every time you have a bug or a regression, you write a test that confirms correct behaviour.
If you can be 100% guaranteed that there indeed is a test for every occurred bug. Sometimes maintainers are not so strict about it.
And some programmers are so good that some issues are self-explanatory and they write good code to note a thing but don't write a test, because implementing the test is more expensive.
very naive. the runtime behavior of a rewrite should be significantly different in all kinds of unpredictable ways nobody see coming or might expect. It is a combination of language semantics, compiler behavior, operating system behavior, file system behavior, driver behavior, ..
So you get other bugs when rewriting in another language without existing tests, got it. This is why I hate all the announcements of "it is rewritten in rust so it is obviously better than the original since it passes all the tests". Edit: and it's an LLM rewrite. Add that to the pile of over hyped messaging.
Software like a Database should have an extensive test bench with concurrency tests, all corner cases etc.
I'm not here running the new version on production to tell the maintainer/devs that my 'production unit tests failed'.
What is this even for logic?
I mean there is balance when i write tests for my production software, but my software is used by me. If i would have a library, i would test everything.
And there was some blog post about another database system were they even virtualized the File access to test cases like when the disk controller stops working.
I agree. I also agree with the sibling reply that -
> every time you have a bug or a regression, you write a test that confirms correct behaviour.
What I fail to see in these rewrites however is - what about new bugs introduced by virtue of this rewrite? I mean it'll have to go through its own challenges in real-world scenarios, right?
And also the amount of people running it in thousands of scenarios. Not sure if these areas can be even tested for, but I guess time will tell (can observe Bun if it breaks somewhere as that’s afaik the first big AI rewrite which got into prod for masses).
A lot of the signal (github, forums, mailing lists, discord, etc.) can be turned into signal. Right now it's easy enough to collect. In future it will be easy enough to cluster and generate preferences, experience, etc.
Every bug report, code change as a result, PR / commit message, PR comment that steers preferences, etc. is solid signal to generate future tests.
The test suite is the result of these years of years of running in production. Every time you fix a bug, you add a non-regression test to ensure you don’t break it again.
In a project like PostgreSQL, those scars are reflected in unit tests demonstrating that they’re fixed. It’d be hard to pass its test suite and not be as robust as the original.
> It’d be hard to pass its test suite and not be as robust as the original.
This is not true, even in principle, even for Postgres itself. You'd be right to say that it'd be hard to pass the test suite and not be robust at all to some extent. But even in Postgres, I bet that you can quite easily introduce a change that will pass the whole test suite but reduce robustness compared to the latest release (for a somewhat silly example, add a call to `exit()` on a timer that's longer than the longest duration test in the suite - that will significantly reduce robustness while still passing the entire test suite).
Sure but these scars/tests are from the original implementation. Just because it doesn't have issues there doesn't mean it didn't bring its own set of issues
This is all well and good in theory, but the number of times I've seen tests that don't actually test what they say they're testing is hard to count. Yes even when you encourage the developers to ensure the test fails first and do TDD. Tests help you ship with confidence but there's usually at least a few that are just passing by pure luck.
So no, I wouldn't judge a rewrite as being equal just because it passes the tests. That said, I don't think that means you shouldn't do it. You just have to be pragmatic about it.
That's precisely what a regression test suite is for. There is a bug, you fix the bug, you add a regression test. So if the test suite is well maintained these real world production scars are reflected in the tests.
100% agree. And I am one of those people that (out of curiosity) am doing something similar. Yes, all tests pass today but tsz is nowhere near a complete project. For tsz it was rather easy to prove "passing all tests" ≠ "it is ready"
Why should a developer use this for anything beyond a pet project? Just because it is written in Rust?
All these "rewritten in rust" projects only reinforce the idea that a significant part of the rust community consists of software talibans and not of engineers who must deliver something that works and is reliable over time.
Well, this approach is more similar to imposing a dogma thank engineering.
Is managing memory safely important? YES
Is managing memory safely the solution to most of the problems? Absolutely not.
Advocating the language ignoring everything else (having as first and only argument that the code was rewritten in rust fully qualify for this case) is dogma and not engineering.
I think this shouldn't be taken too seriously, from what I understand it's an exploration of what's possible with today's LLMs.
You're right to talk about the trend though, because what it shows is how the cost of re-writing well covered project has completely crashed, so that in itself is a learning.
I have no issues recognizing that I had memory-related problems in production (I program embedded systems in C).
But most of my issues were related to concurrency and data sanification, especially when the other end of communication fails with unexpected behavior. These bugs are nastier than memory.
So, I have pointers, and I am not afraid to use them.
Not sure it’s so simple. I think close to 100% of new ambitious projects are going to leverage AI at least to some degree. I know a couple that have strict no-AI policies (e.g. Zig), but it’s a tiny minority i think.
So how much AI usage does it make it an “AI rewrite”?
Dunno. I got rather the impression that it's ambitious single-developer projects with no intention of maintenance which leverage those 'AI' code generators the most.
Who wants to contribute to an unmaintainable code base?
I agree but I think from Bun we learned that a project with really good tests and enough tokens can be converted from one language to another quite good!
It is more and more the future. No human would want to rewrite one technology to another because it is too marginal a gain. AI on the other hand does not give a shit.
Is there any measurable difference in quality between the two, or are you just going on "vibes"? Is there a correlation between the quality of the manually written code and AI generated code driven by the same dev?
Such crude takes only cause unnecessary friction. If you have a black box that spits out code, and you are unable to distinguish the quality between a top tier dev and an AI inside the black box, then the distinction is unnecessary. Most of the code on the internet is already a black box to you. What percentage of code running on your machines have you vetted by who wrote it and code quality?
AI coding isn't going anywhere and will likely end up generating most code going forward so instead of rejecting it outright or arbitrarily categorizing it we need to focus on solid quantitative and qualitative measures of code and functionality regardless of who wrote it.
> Is there a correlation between the quality of the manually written code and AI generated code driven by the same dev?
Aren't you making a strawman argument ? AFAIK this project is not made by an official PostgreSQL core developer, so the entire premise of your argument is invalid.
> Is there a correlation between the quality of the manually written code and AI generated code driven by the same dev?
If the dev doesn't vet the code, it doesn't matter how good quality a dev they would be if they wrote the code - they didn't. Sure, the dev would probably drive the initial architecture discussion better and some people are using AI in small batches with tests and vetting everything, but some previously great devs are throwing in PRs that touch hundreds of files at once with one commit.
A lot of people I previously considered great developers have become people I would not recommend for a job in the past 2-3 years.
> If you have a black box that spits out code, and you are unable to distinguish the quality between a top tier dev and an AI inside the black box, then the distinction is unnecessary.
Sure, but this is just begging the question. If nobody could tell, the term 'slop' wouldn't have become so popular.
How is the performance compared to regular PostgreSQL?
I know it says it is not performance optimized yet, but if this succeeds, will it only bring more "memory safety" or is there a serious performance gain as well?
You are now at 0.1%... now submit upstream in sensible chunks (function or maybe file/module), waiting for people to review (a few per week, maybe) and approve/merge.
Because Rust is what's cool these days. Don't you wanna be cool? Also Rust has memory safety things that C++ doesn't have, so there's a class of bugs that can't happen in the Rust version. That doesn't mean the Rust version is 100% bug free, but just that it's not vulnerable to that class of bugs. So it's a good thing for security reasons if you're running a database server somewhere that attackers could get at it. There might be performance benefits down the road if they choose to focus on that.
I think we will actually see some successful projects coming out of this. There are definitely people who want x old project in this new/better programming language and who are willing to put effort into maintaining it not just doing one off port.
I'm starting to get a bit of fatigue for these projects that boil down to just "I asked Claude to re-write this code into a new language that's in vogue right now!"
I really don't understand why this is needed outside of an opportunity to show how impressive LLMs can be when working within large codebases, but even then people in the comments are finding bizarre implementation choices that a human developer wouldn't make. I'll stick with Postgres and its - gasp - C implementation for now, thanks.
But that's the thing, without the decades of work, it wouldn't BE trivial.
Everyone is standing on the shoulders of those which came before. If LLMs allow us to combine the incredible decades of effort and knowledge and experiences that's gone into building something as great as Postgres, and take that and combine the experience and philosophy that has led to the creation of a language that potentially provides tangible benefits, and for far less human time and effort that it would have otherwise taken...surely something that should be celebrated as absolutely incredible?
I don't really understand how "written by AI" and "for learning purposes" can ever be compatible. What exactly does one learn from typing "Rewrite this in Rust, make no mistakes" into a terminal?
What would be interesting is if they found a memory unsafe bug. Postgres is a perfect case study of 30 years of C with a bit of CPP; if rewriting in a safer language didn't find anything...
Woah! AGPL? That's interesting. I think Postgres has shown an open source SQL server didn't need a copy-left license to develop sustainably, so I'm not entirely aure about that, but I do like the license in general.
When the software consists entirely of ~$1000 worth of Claude credits and ~40 hours of developer time prompting and curating it, literally what does it matter what license the resulting 100k LoC artifact is provided under?
Copyleft and the whole software licensing ecosystem only matter when producing that software actually requires serious human effort and dedication.
For my machine translation of SQLite to Go I added this to the README as to licencing:
Most of the code here is machine translated using wasm2go. As such, the original authors retain copyright and the original licenses remain in effect. Everything else is licensed under MIT-0.
The translator (wasm2go) has a licence chosen by, and a copyright notice from, me. Makes no sense for the translated code.
We had one for SQLite (which is SQL-ite btw, not SQ-Lite which doesn't make any sense) via Turso, no wonder we see the same for Postgres. Personally I do want to see libraries be in as much memory safe languages as possible.
What is the future of this? Code is not the same as a viable open-source project with a community, contributors, advocates, users and funding, even if it's perfect code.
Even though I'm sure it won't be easy to convince the Postgres project to switch to Rust, I do think that trying would be time better spent.
The return type in the rewrite is both some sort of Error tagged union that supports the Try machinery in Rust; but, it also contains a boolean that apparently must be checked; or something. It seems labyrinthical and possibly broken and terrible.
It is a feature in Rust, not a bug :-) (I know you didn't say it is a bug.)
The error-tagged union is PgResult<bool> - which means it contains bool as the result if things go well. (The other part in the union is of course the error.)
In the original function also, it is returning a boolean: "bool has_subclass".
So anyway you have to check for the boolean as part of the logic. That is what it is doing.
Yes, but the original boolean seems to have been used for error handling, and the tagged union is also used for error handling. Why have both simultaneously in the same function instead of just one of the two?
From what I skimmed manually, not that many, but the code itself seems labyrinthical. Like, why have both Rust Try-supporting Error-like tagged union, but also booleans, for error handling, in the same function?
One of the things I'd typically do is peek at the commit history. Seeing what people worked on and how they did it tends to say a lot about a project. But with LLMs generating 7101 commits in less than a month that isn't feasible. Even looking at a single day is way too much [1]. It probably also doesn't make sense since the commits content won't tell you much anyway.
ps. How do you easily get to the first commit in a repo on GitHub? Browsing commit history feels rather tedious
[1] - https://github.com/malisper/pgrust/commits/main/?since=2026-...
Most extensive test suites are exactly production scars: every time you have a bug or a regression, you write a test that confirms correct behaviour.
SQLite is a good example to bring up because its extensive closed-source tests are what’s often cited as being what keeps people from forking it. (Turso did it, though, but it takes a company to deliver some guarantee of equivalent diligence.)
And yes, years and years of running.
Getting an extensive test suite passing is certainly orders of magnitude better than having no test suite at all, but it still doesn't tell you as much as you need to know. I would absolutely never trust an LLM Postgres rewrite (in any language) in production based on "only" Postgres's test suite passing.
This space of things is astronomically larger than the space of things expressly covered by any test suite.
"Program testing can be used to show the presence of bugs, but never to show their absence." -Edsger W. Dijkstra
While not an exact fit of an analogy, those tests patch what was a problem with Postgres in the wild. What it doesn't cover are the things that worked in Postgres without tests, but may fail in port and go undetected.
I think this is also where the real work is. A rewrite is one thing, that you can show off with a flashy blogpost. The maintenance, for years to come, won't be of that nature yet it still requires as much work.
If you can be 100% guaranteed that there indeed is a test for every occurred bug. Sometimes maintainers are not so strict about it.
And some programmers are so good that some issues are self-explanatory and they write good code to note a thing but don't write a test, because implementing the test is more expensive.
They aren't the bugs you get when you write it in Rust.
The kind of bugs you get are usually a function of the problem, language, implementation approach.
Software like a Database should have an extensive test bench with concurrency tests, all corner cases etc.
I'm not here running the new version on production to tell the maintainer/devs that my 'production unit tests failed'.
What is this even for logic?
I mean there is balance when i write tests for my production software, but my software is used by me. If i would have a library, i would test everything.
And there was some blog post about another database system were they even virtualized the File access to test cases like when the disk controller stops working.
> every time you have a bug or a regression, you write a test that confirms correct behaviour.
What I fail to see in these rewrites however is - what about new bugs introduced by virtue of this rewrite? I mean it'll have to go through its own challenges in real-world scenarios, right?
Every bug report, code change as a result, PR / commit message, PR comment that steers preferences, etc. is solid signal to generate future tests.
This is not true, even in principle, even for Postgres itself. You'd be right to say that it'd be hard to pass the test suite and not be robust at all to some extent. But even in Postgres, I bet that you can quite easily introduce a change that will pass the whole test suite but reduce robustness compared to the latest release (for a somewhat silly example, add a call to `exit()` on a timer that's longer than the longest duration test in the suite - that will significantly reduce robustness while still passing the entire test suite).
So no, I wouldn't judge a rewrite as being equal just because it passes the tests. That said, I don't think that means you shouldn't do it. You just have to be pragmatic about it.
Even a 100% test coversge is far away from verifying all behaviour.
"Program testing can be used to show the presence of bugs, but never to show their absence!"
The biggest lie of software engineering is that everything can be testable with tests. That a 100% test coverage is an indicator of quality software.
https://github.com/tsz-org/tsz/
All these "rewritten in rust" projects only reinforce the idea that a significant part of the rust community consists of software talibans and not of engineers who must deliver something that works and is reliable over time.
Cue some story here on a bank or airline somewhere still relying on cobol backend servers.
These LLM conversions really seem to make modernization of large parts software layers possible!
I will note that, very funny
Is managing memory safely important? YES
Is managing memory safely the solution to most of the problems? Absolutely not.
Advocating the language ignoring everything else (having as first and only argument that the code was rewritten in rust fully qualify for this case) is dogma and not engineering.
You're right to talk about the trend though, because what it shows is how the cost of re-writing well covered project has completely crashed, so that in itself is a learning.
But most of my issues were related to concurrency and data sanification, especially when the other end of communication fails with unexpected behavior. These bugs are nastier than memory.
So, I have pointers, and I am not afraid to use them.
So how much AI usage does it make it an “AI rewrite”?
Who wants to contribute to an unmaintainable code base?
It’s mostly grunt work and LLMs are well suited for translation tasks (iirc transformers arch was originally invented for translation)
It was trained on all code the code that could be found.
Not just code written by genius programmers like Carmack and Bellard.
Given that it's average, I'd prefer a human coder above average :)
Then, by giving them context or by post-training, you can make them sample non-average parts of the distribution they learned.
How do you derive that something is "below average" or "average" or "above average"?
I've been programming a long time and considered myself among the top in my domain and AI agents using like GPT 5.5 etc. are much better than me.
Is the domain bullshiting?
Ex falso quodlibet
> I've been programming a long time and considered myself among the top in my domain
I am not trying to attack you, but you considered yourself that... I don't know whether you actually were and frankly I don't care.
Such crude takes only cause unnecessary friction. If you have a black box that spits out code, and you are unable to distinguish the quality between a top tier dev and an AI inside the black box, then the distinction is unnecessary. Most of the code on the internet is already a black box to you. What percentage of code running on your machines have you vetted by who wrote it and code quality?
AI coding isn't going anywhere and will likely end up generating most code going forward so instead of rejecting it outright or arbitrarily categorizing it we need to focus on solid quantitative and qualitative measures of code and functionality regardless of who wrote it.
Aren't you making a strawman argument ? AFAIK this project is not made by an official PostgreSQL core developer, so the entire premise of your argument is invalid.
If the dev doesn't vet the code, it doesn't matter how good quality a dev they would be if they wrote the code - they didn't. Sure, the dev would probably drive the initial architecture discussion better and some people are using AI in small batches with tests and vetting everything, but some previously great devs are throwing in PRs that touch hundreds of files at once with one commit.
A lot of people I previously considered great developers have become people I would not recommend for a job in the past 2-3 years.
> If you have a black box that spits out code, and you are unable to distinguish the quality between a top tier dev and an AI inside the black box, then the distinction is unnecessary.
Sure, but this is just begging the question. If nobody could tell, the term 'slop' wouldn't have become so popular.
I know it says it is not performance optimized yet, but if this succeeds, will it only bring more "memory safety" or is there a serious performance gain as well?
I really don't understand why this is needed outside of an opportunity to show how impressive LLMs can be when working within large codebases, but even then people in the comments are finding bizarre implementation choices that a human developer wouldn't make. I'll stick with Postgres and its - gasp - C implementation for now, thanks.
Everyone is standing on the shoulders of those which came before. If LLMs allow us to combine the incredible decades of effort and knowledge and experiences that's gone into building something as great as Postgres, and take that and combine the experience and philosophy that has led to the creation of a language that potentially provides tangible benefits, and for far less human time and effort that it would have otherwise taken...surely something that should be celebrated as absolutely incredible?
https://github.com/malisper/pgrust/blob/3646a73515a5e4ac7d0b...
https://github.com/malisper/pgrust/blob/3646a73515a5e4ac7d0b...
In fact from a porting effort this is the first blog post I would expect. Not that the hey we successfully did it.
Copyleft and the whole software licensing ecosystem only matter when producing that software actually requires serious human effort and dedication.
For my machine translation of SQLite to Go I added this to the README as to licencing:
Most of the code here is machine translated using wasm2go. As such, the original authors retain copyright and the original licenses remain in effect. Everything else is licensed under MIT-0.
The translator (wasm2go) has a licence chosen by, and a copyright notice from, me. Makes no sense for the translated code.
DST systems such as Antithesis can definitely help.
Even though I'm sure it won't be easy to convince the Postgres project to switch to Rust, I do think that trying would be time better spent.
Rust:
https://github.com/malisper/pgrust/blob/3646a73515a5e4ac7d0b...
Original:
https://github.com/postgres/postgres/blob/df293aed46e3133df3...
Usage:
https://github.com/malisper/pgrust/blob/3646a73515a5e4ac7d0b...
The return type in the rewrite is both some sort of Error tagged union that supports the Try machinery in Rust; but, it also contains a boolean that apparently must be checked; or something. It seems labyrinthical and possibly broken and terrible.
The error-tagged union is PgResult<bool> - which means it contains bool as the result if things go well. (The other part in the union is of course the error.)
In the original function also, it is returning a boolean: "bool has_subclass".
So anyway you have to check for the boolean as part of the logic. That is what it is doing.
I wonder how many "unsafe" blocks are in there...
https://github.com/malisper/pgrust/blob/3646a73515a5e4ac7d0b...
https://github.com/malisper/pgrust/blob/3646a73515a5e4ac7d0b...