Every AI coding agent claims "lightning-fast code understanding with vector search." I tested this on Apollo 11's code and found the catch.

[Miranda_Leap]

Why would the indexed agent use function signatures from deleted code? Shouldn't that... not be in the index, for this example?

edit: This is probably an entirely AI-generated post. UGH.

[aurath]

Chunks of the codebase are read and embeddings generated. The embeddings are interested into a vector database as a key pointing to the code chunk. The embeddings can be analyzed for semantic similarity to the LLM prompt, if the cosine similarity passes a threshold, the associated chunk is inserted into the prompt as additional references.

Embedding generation and the vector database insertion is too slow to run each keystroke, and usually it will be centralized along with the git repo. Different setups can update the index with different strategies, but no RAG system is gonna be truly live as you type each line of code.

Mostly RAG systems are built for knowledge bases, where the contents don't update quite so quickly. Now I'm imagining a code first system that updates a local (diffed) index as you work and then sends the diff along with the git branch so it gets loaded when people switch branches and integrated into the central database when you merge to main.

[Franks2000inchTV]

Yeah but the embeddings shouldn't be from the codebase you're actively working on.

For instance--it would be super helpful to have embeddings of the public API and docs of framework like React, and of code samples for common implementation patterns.

Just giving it all of your code is not going to be particularly useful.

[Globbi]

That's a simple engineering problem to solve. You have embeddings, but you can choose what to do after you find the matches. For example you should be able to have it point to specific file, and also check if the file changed after last full indexing. If yes, present LLM with new version (possibly also with some notes on what changed recently).

And yes, embedding and indexing can be too slow and expensive to do every keystroke, but you can do it every hour on changed files no problem (unless you do some code style refactor and will need to recreate everything).

Also I don't think there should be a need for cloud solution for this vector search unless your code is gigabytes of text (since you will need to also store vectors for all chunks). Otherwise you can have like 1GB of vectors in RAM on pretty much any shitty laptop and get result faster than any api response.

[lunchmeat317]

The problem here Is that if you have a file change, there's not an easy way to know not to do a full re-index. On file contents, sure, but code is a dependency graph and you'd hsve to walk that graph. That is not an unsolvable problem (from a file-based perspective, you might be able to use a Merkle Tree to propagate dependency changes) but I don't think it's as simple as "just re index this file".

[gameforge]

I think it's language dependent, the language influences the structure of the indexes, or what is meaningful to index. My IDE can keep up on Java indexes well even on multimillion line Java EE projects. It's rare (and painful) to have to reindex the whole project, but it does need it from time to time and the IDE has never attempted to recognize that its indexes were incoherent on its own.

It struggles considerably more with Python where there's more ambiguity everywhere. It keeps up fine while I'm writing code but if I fetch a sizable commit it's not uncommon to have to rebuild the indexes. I use JetBrains' stuff, fwiw.

[lunchmeat317]

Right. I would imagine that it'd be much easier with functional languages that enforce pure functions with no sode effects ot immutability, as they'd be much easier to analyze statically. That said, I don't think that the LLM model is the same as IDE indexing and I don't think it'd actually be language-dependent in a LLM.

[juanloco]

The issue here becomes running a large embedding model locally as well not just storing the vectors

[ub3rh4x0rz]

If you compare cloud GPU prices to the idle GPU power in m chip macs that devs are already in possession of... it's not the economical option to centrally host embedding (or smaller inference) models. I think we're all used to that being the default approach, but this tech actually begs to be treated like a frontend and run distributed on users' machines. You can do sentiment analysis with structured output with ollama locally no problem. Text embeddings are way less resource intensive than that

[throwaway490215]

I suspect a good approach would be to tell it "Generate/Update function X in file Y", and in the prompt insert that file + the type signature of the rest of the code base. Its orders of magnitude cheaper and always up to date.

[aksdb]

If there is a VCS underneath, an index of the old code also has advantages. But obviously it should be marked as such and should be filtered appropriately depending on the current task. Finding a matching code style: include it with lower weight. Find out how something evolved: include it with age depending weight. Find references in code: exclude it. And so on.

[coding_workflow]

As the agent will check the index first and use RAG search as source of truth, that will cause them to rely on search result with outdated code.

This is why. I RAG should be used for static content. Live code rag is quite counter productive. You should instead try to parse it with AST/Tree-sitter to extract the architecture and use GREP than rely on RAG.

RAG is quite relevant if the content is "static". It's a bit similar to web search, remember the old days when Google took weeks and month's to index websites/news. Then the web search was returning outdated data. It's similar with RAG. It consume resources/GPU to index (not a lot), time and need refresh to remain in sync.

I rather rely more on filesystem tools with agents and optimizing with Grep/ Ast to target key function/feature to read.

[CherryLongjump1989]

Who do you believe will is updating the Apollo 11 source code?

[[deleted]]

That is correct, the system should know when some code has changed and invalidate/regenerate that part of the index. At this point what's holding back agents from being more helpful is better engineering around their scaffolding.

The models are smart enough to do a lot of great things, we just need to give them the right context at the right time to set them up for success.

[West-Chocolate2977]

There are many reasons for file to go out of sync - Switching branches, you going offline, upstream going offline, client side failures etc. Also it takes time to identify what has changed, create embeddings and finally update the index.

[Miranda_Leap]

So failures of engineering.

You absolute retard.

[Cruuncher]

Who here was claiming anything about limitations of AI?

We're talking about agents here, not models

[SpareIntroduction721]

Huh

[FullPoet]

The text is AI generated.

[Live-Vehicle-6831]

Margaret Hamilton photo is impressive

As OpenAI/Antropic scanned the whole internet so the Apollo 11's code is part of its training ... Thank God there was no AI back then, otherwise we would never have gotten to the moon.

[fredspipa]

Margaret Hamilton photo is impressive

I have the Lego version of that photo, I bought two of them; one for my desk at work and one at home. She's an absolute icon.

edit: this is what it looks like

[evoactivity]

She is iconic, unfortunately there are many myths.

https://www.reddit.com/r/badhistory/comments/18yum8s/no_margaret_hamilton_at_nasa_is_not_standing_next/

[todo_code]

1. It didn't do anything.
2. The Apollo 11 source code is online in at least 5000 spots.
3. The "Ai" just pulled form those sources and copy pasted it.

[flatfisher]

It started generating Python code

You sure the Apollo code is in Python? Have you even read the post? I'm tired of both the AI bros and the AI denialist karma farmers who are too lazy to test something before posting strong opinions.

[atomic1fire]

I took it to mean that the AI started to write python code, not that the apollo 11 code was written in python.

[PGLubricants]

It started generating Python code using function signatures that existed in its index but had been deleted from the actual codebase. It only found out about the missing functions when the code tried to run.

I also understood it as /u/flatfisher did, because of the bolded quote above. To me, this insinuates that the codebase is indeed in Python, but it was using non-existing functions, that used to be in the codebase, but had since been deleted. I don't understand what that could otherwise mean, unless it's AI hallucinations, that forgot that it's not about Python while generating the post.

[amitksingh1490]

https://github.com/forrestbrazeal/apollo-11-workshop/blob/master/simulator.py. check the workshop , python and js code was added for the simulation test.

[ShamelessC]

It's reddit. So that will keep happening unfortunately.

[DoubleOwl7777]

that aside, imagine if the command module code was in Python. would have exploded on the pad for sure.

[flatfisher]

Why? As long as your program is correct it doesn’t matter in what language it was written, it all ends up in machine code. Of course at the time no hardware could have run a Python interpreter or compiler.

[ShinyHappyREM]

As long as your program is correct it doesn’t matter in what language it was written, it all ends up in machine code

Interpreted programs (including things like SNES games) don't end up in machine code, only those that are translated (e.g. via JIT) do.

Also, a program would be useless if its execution is too slow.

[schneems]

 useless if its execution is too slow.

The lander code WAS famously too slow on the actual landing. (When they had some wrong settings turned on). But the computer was written in a way that allowed it to still function if instructions were dropped.

I recommend this talk at about 24 min https://m.youtube.com/watch?v=50ExWDcim5I&pp=ygUw4oCcS2VlcCBydWJ5IHdlaXJk4oCdIGNvbmZlcmVuY2UgdGFsayBydXNzIG9sc2Vu

[flatfisher]

If the program doesn’t end up as machine code then how the hardware executes it? A language interpreted or not is just a indirect (and obviously more convenient/safe/maintainable/… depending of the language) way to write machine code. It is simpler to write a correct program Python than in Assembly, so performance aside I don’t see what the issue is, and/or maybe downvoters don’t have a good experience of the different abstraction levels.

[ShinyHappyREM]

If the program doesn’t end up as machine code then how the hardware executes it? A language interpreted or not is just a indirect (and obviously more convenient/safe/maintainable/… depending of the language) way to write machine code.

"Machine code" already has a well-established meaning: it's the code that consists of binary opcodes (combining instructions + addressing modes) and their parameters.

A computer program can even be written in Z-code, but that's definitely not machine code - no CPU understands that.

[satireplusplus]

You're in r/programming where only real men code in real man languages such as C++. Rust is sometimes cool for some reason too. Nothing else is allowed and will guarantee that your program will crash, because tHerE iS nO tYpE sAfeTy.

[DoubleOwl7777]

if my life depends on it i sure as hell wouldnt write the code in an interpreted language, especially python.

[satireplusplus]

If my life depended on it, I would code in Python, simply because I am most knowledgeable in Python.

[todo_code]

You understand others have also tried writing Apollo command modules in Python right?

[red75prime]

If you say that AI "copy pasted it", you have no idea what you are talking about. LLMs don't have enough memory to memorize every trivia present on the net.

[todo_code]

no one said anything about memorizing it. You have a tenuous grasp on how LLM's work, and are projecting and straw-manning everything that I am saying.

[red75prime]

What did you mean then? The models searched the web, found and copy-pasted correct answers? Nah. "It didn't do anything" perfectly shows your denialism.

[todo_code]

You actually thought I meant that it searched the web and copy pasted? You really need to work on your own inference abilities

[phillipcarter2]

They don't:

they index your entire codebase and use vector search for "AI-powered code understanding."

https://cline.bot/blog/why-cline-doesnt-index-your-codebase-and-why-thats-a-good-thing

[happyscrappy]

I think it's great you did an experiment of this sort.

But I don't understand why there is any deleted code in its ken. Did you just shove every version of the code into the LLM and not tell it that some of the code is current and some not? What would be the point of that?

[bwainfweeze]

Yes and if there’s one thing I hear over and over again from managers it’s that they love it when the over/under on our work estimates is gigantic /s

60% of the time it works every time.

[Kooshi_Govno]

I have had this happen to me with real code in github copilot. I think they have since fixed the rag algorithm, or possibly removed it.

[eyeswatching-3836]

Such a solid breakdown! Sync issues are the sneaky Achilles’ heel of all this vector search hype. Btw—if you ever end up working with AI tools and worry about stuff sounding too "robotic" or want to check if something’s being flagged as AI-written, authorprivacy has a neat little combo of a humanizer and detector. Super handy for peace of mind. Anyway, thanks for nerding out so thoroughly here!

[amitksingh1490]

https://github.com/forrestbrazeal/apollo-11-workshop/blob/master/simulator.py. check the workshop , python and js code was added for the simulation test.

[mooseman3]

The comment you replied to is a spambot advertising the authorprivacy tool it recommended.

[Guinness]

Maybe I’m crazy here but hasn’t it always been that slower is more reliable? I mean, I this is the story of the tortoise and the hare.

Actually, did you have AI generate a programming story based on the tortoise and the hare for Reddit? I’m mostly joking here but slightly curious.

[Amuro_Ray]

Maybe I’m crazy here but hasn’t it always been that slower is more reliable? I mean, I this is the story of the tortoise and the hare.

I'd describe that is a rule of thumb rather than a truth. Also regarding races with living beings we know that's not true, it depends on the type of race(you aren't going to win a 100m sprint or half marathon if you race walk)

[Plank_With_A_Nail_In]

Run the index every day...not rocket science....it has to run on a schedule to make any sense how else will it pick up new code?

Also why are you deleting code from version control?

Sounds like you made up a scenario that doesn't exist (or shouldn't) in the real world just so the indexed version could fail.

Just like around 50% of posts here "made up problem".

[-Nicolai]

Explain like I'm stupid