rkochanowski
Joined 4 months ago
Joined 4 months ago
To give more context, the current version is already an optimized one I considered good enough and didn't spend more time on it. In the first attempt, I used a vector database with indexes, trying to query for similar vectors. This was uselessly slow even in medium-sized repos. The brute-force NumPy solution is a significant improvement, making it faster than other calculations like clustering.
"vectors are not loaded into memory at once" is not true, I had in mind splitting computation into blocks.
One possible simple optimization is to use 16-bit floats in vector instead of 32-bit. I used this in a different project (halfvec in pgvector) without affecting results.
1536-dim embeddings from your case also can be reduced. This large vector usually doesn't give much benefit compared to smaller ones. And this is something I will compare in my own tests.
* cluster-01.md has the highest similarity, and jscpd probably will detect this too.
* cluster-10.md has the lowest similarity still above the threshold, and I don't think jscpd will detect this as clones. Because they are not clones, this is a false positive that needs to be discarded. But in other cases this kind of similar code may be worth acting on.
I didn't compare with jscpd because I don't consider it a competition. Embedding-based duplication detection works differently, gives different results and has its own trade-offs.
The goal of the tool is to also detect code that is similar and behaves differently. There are not ideal duplicates, but still a code that can be refactored, abstracted, or fixed (because the variance may be the result of bug).
Embedding calculation is also outsourced externally: it's only a simple API call with a LiteLLM wrapper.
"brute-force similarity search" and O(n^2) may sound scary, but it works fine and this is not a bottleneck. For large projects, other parts are much slower, which has room for improvement. [1] is an implementation you probably saw. It uses NumPy, spreads work across all CPU cores and there is also a split into blocks (block_size = 1000). In larger sets, all vectors are not loaded into memory at once. Where I need to be honest, I didn't measure actual memory usage. I just tested this on large repos, so I'm aware of bottlenecks.
From my perspective, this is the easiest part. Code extraction, chunking, applying boost, clustering, generating report and designing everything as a single user-friendly tool is a real challenge. Architectural and product decisions are more difficult than implementation and solving performance issues.
[1] https://github.com/rafal-qa/slopo/blob/v0.3.0/src/slopo/anal...
jscpd is advertised as "Copy/paste detector", Slopo is advertised as "non-exact code duplication".
Slopo also detects copy/pasted code, but this is not the main goal and the report focuses more on similar code units.
Deduplication backend is the easiest part of the tool and it doesn't need any additional libraries. Just calculate embeddings and find close pairs. The complexity is everything around.
Using local models is worth considering and the tool already uses the LiteLLM wrapper, allowing it to configure different models, including local. I left this part for the user.
1. The tool uses only cosine similarity plus boost depending on distance in the codebase.
2. Classification with LLM. This can be done by coding agent used with project giving better results than integrating this pass in the tool. LLMs used for coding are pretty good.
I assumed that this is not a problem I need to solve inside the tool. I'm aware this is not deterministic, but this is by design.
Regarding information about raw similarity: currently, the score (raw similarity + boost) is visible in the report, so this value can be configured based on data. The raw similarity threshold can also be configured, but it's not displayed. I will think about how to handle this.
But I plan to do my own analysis of different embedding models in the context of code similarity detection. Including BM25 in the comparison is a very good idea.
Skipping the extraction of conditional branches was my decision to not overcomplicate the first versions, which was intended to validate the idea. I will add this in future versions because I agree it's needed for large functions.
I don't think it needs configurable granularity. In the current version, there is an analogous mechanism: when functions are nested, both outer and inner are embedded separately. When both are similar to each other, this pair is excluded. Inner or outer functions can appear in results depending on similarity to other units.
Regarding comments, they are removed and I will think about handling them. The challenge is not with extraction, but with how to present this in a report. This may be a nice addition because coding agents often add comments.
Thanks for the feedback.
The code-specialized model I recommended based on the provider's benchmark turned out to be one of the worst-performing in this use case. But their general-purpose model showed very good results.
Data confirmed that small specialized models can outperform big providers. It showed that the same model variant with a size of 3x more parameters has no practical difference. The dimension of a vector can indeed be reduced several times without any noticeable loss of quality.
All code snippets used in the benchmark are available on https://github.com/rafal-qa/embedding-benchmark