The point about synthetic query generation is good. We found users had very poor queries, so we initially had the LLM generate synthetic queries. But then we found that the results could vary widely based on the specific synthetic query it generated, so we had it create three variants (all in one LLM call, so that you can prompt it to generate a wide variety, instead of getting three very similar ones back), do parallel search, and then use reciprocal rank fusion to combine the list into a set of broadly strong performers. For the searches we use hybrid dense + sparse bm25, since dense doesn't work well for technical words.
This, combined with a subsequent reranker, basically eliminated any of our issues on search.
> For the searches we use hybrid dense + sparse bm25, since dense doesn't work well for technical words.
One thing I’m always curious about is if you could simplify this and get good/better results using SPLADE. The v3 models look really good and seem to provide a good balance of semantic and lexical retrieval.
Boy, that should not be the concern of the end user (developer) but those implementing RAG solutions as a service at Amazon, Microsoft, Openai and so on.
At Microsoft, that's all baked into Azure AI Search - hybrid search does BM25, vector search, and re-ranking, just with setting booleans to true.
It also has a new Agentic retrieval feature that does the query rewriting and parallel search execution.
So few developers realize that you need more than just vector search, so I still spend many of my talks emphasizing the FULL retrieval stack for RAG.
It's also possible to do it on top of other DBs like Postgres, but takes more effort.
I am working on search but rather for text-to-image retrieval, nevertheless, I am curious if by that's all baked into Azure AI search you also meant synthetic query generation from the grandparent comment. If so, what's your latency for this? And do you extract structured data from the query? If so, do you use LLMs for that?
Moreover I am curious why you guys use bm25 over SPLADE?
Yes, AI Search has a new agentic retrieval feature that includes synthetic query generation: https://techcommunity.microsoft.com/blog/azure-ai-foundry-bl...
You can customize the model used and the max # of queries to generate, so latency depends on those factors, plus the length of the conversation history passed in. The model is usually gpt-4o or gpt-4.1 or the -mini of those, so it's the standard latency for those.
A more recent version of that feature also uses the LLM to dynamically decide which of several indices to query, and executes the searches in parallel.
That query generation approach does not extract structured data. I do maintain another RAG template for PostgreSQL that uses function calling to turn the query into a structured query, such that I can construct SQL filters dynamically.
Docs here:
https://github.com/Azure-Samples/rag-postgres-openai-python/...
AI Search team's been working with the Sharepoint team to offer more options, so that devs can get best of both worlds. Might have some stuff ready for Ignite (mid November).
I know :( But I think vector DBs and vector search got so hyped that people thought you could switch entirely over to them. Lots of APIs and frameworks also used "vector store" as the shorthand for "retrieval data source", which didn't help.
I believe that Azure AI Search currently uses lucene for BM25, hnswlib for vector search, and the Bing re-ranking model for semantic ranking. (So, no, it does not, though features are similar)
Yep- that's all best practice. I want to know if we could push performance further- routing the query to different embedding models or scoring strategies, or using multiple re-rankers- still feels like the process is missing something.
OP. The way you improve it is move away from single shot semantic/keyword search and have an agentic system that can evaluate results and do follow-up queries.
I must be missing something, this says it can be self-hosted. But the first page of the self-hosting docs say you need accounts with no less than 6 (!) other third-party hosted services.
We have very different ideas about the meaning of self-hosted.
> For example - if a "self hosted" service supports off-site backups is it self hosted or just well designed?
There is a big difference between communicating with external services (your example) vs REQUIRING external services (what parent is complaining about).
If in your example the system can run correctly with just local backups I would consider it self-hosted.
That was my observation as well. To be fair their business is to sell a hosted version, they’re under no obligation to release a truly self hosted version.
I’ve never worked in such a space where the deployed environment had unfettered internet access, no access at all actually.
I’ve probably missed a huge wave of programming technology because of this, and I’ve figured out a way to make it work for a consistent paycheck over these past 20 years.
I’m also not a great example, I think I’ve watched 7 whole hours of YouTube videos ever, and those were all for car repair help.
I shy away from tech that needs to be online/connected/whatever.
The big LLM-based rerankers (e.g. Qwen3-reranker) are what you always wanted your cross-encoder to be, and I highly recommend giving them a try. Unfortunately they're also quite computationally expensive.
Your metadata/tabular data often contains basic facts that a human takes for granted, but which aren't repeated in every text chunk - injecting it can help a lot in making the end model seem less clueless.
The point about queries that don't work with simple RAG (like "summarize the most recent twenty documents") is very important to keep in mind. We made our UI very search-oriented and deemphasized the chat, to try to communicate to users that search is what's happening under the hood - the model only sees what you see.
I agree completely with your point, especially the difficulty of developing the user's mental model for what's going on with context and the need to move away from chat UX. It's interesting that there are still few public examples of non-chat UIs that make context management explicit. It's possible that the big names tried this and decided it wasn't worth it -- but from comments here it seems like everyone that has built a production RAG system has come to the opposite conclusion. I'm guessing the real reason is otherwise: likely for the consumer apps controlling context (especially for free users) and inference time is one of the main levers for cost management at scale. Private RAGs, on the other hand, are more concerned with maximizing result quality and minimizing time spent by employee on a particular problem with cost per query much less of a concern --- that's been my experience at least.
I wish there was more info on the article about actual customer usage - particularly whether it improved process efficiency. It's great to focus on the technical aspects of system optimization but unless this translates to tangible business value it's all just hype.
Does anyone know how to do versioning for embeddings? Let’s say I want to update/upsert my data and deliver v6 of domain data instead of v1 or filter for data within a specified date range. I am thinking of exploring context prepending to chunks.
Your vector store should let you store the original text as well as metadata, where you can store the version. For e.g. turbopuffer lets you filter on attributes https://turbopuffer.com/docs/query#filtering
Not here to schlep for AWS but S3 Vectors is hands down the SOTA here. That combined with a Bedrock Knowledge Base to handle Discovery/Rebalance tasks makes for the simplest implementation on the Market.
Once Bedrock KB backed by S3 Vectors is released from Beta it'll eat everybody's lunch.
OP. We migrated to GPT-5 when it came out but found that it performs worse than 4.1 when you pass lots of context (up to 100K tokens in some cases). We found that it:
a) has worse instruction following; doesn't follow the system prompt
b) produces very long answers which resulted in a bad ux
c) has 125K context window so extreme cases resulted in an error
Again, these were only observed in RAG when you pass lots of chunks, GPT-5 is probably a better model for other taks.
Embedding based RAG will always just be OK at best. It is useful for little parts of a chain or tech demos, but in real life use it will always falter.
The difference is this feature explicitly isn't designed to do a whole lot, which is still the best way to build most LLM-based products and sandwich it between non-LLM stuff.
rag will be pronounced differently ad again and again. it has its use cases. we moved to agentic search having rag as a tool while other retrieval strategies we added use real time search in the sources. often skipping ingested and chunked soueces. large changes next windows allow for putting almost whole documents into one request.
Most of my ChatGPT queries use RAG (based on the query ChatGPT will decide if it needs to search the web) to get up to date information about the world. In reality life it's effective and it's why every large provider supports it.
OP here. We've been working on agentset.ai full-time for 2 months. The product now gets you something working quite well out of the box. Better than most people with no experience in RAG (I'd say so with confidence).
Ingestion + Agentic Search are two areas that we're focused on in the short term.
I'm not sure there is a chunker in this repo. The file you linked certainly doesn't seem to perform any chunking, it just defines a data model for chunks.
The only place I see that actually operates on chunks does so by fetching them from Redis, and AFAICT nothing in the repo actually writes to Redis, so I assume the chunker is elsewhere.
> Reranking: the highest value 5 lines of code you'll add. The chunk ranking shifted a lot. More than you'd expect. Reranking can many times make up for a bad setup if you pass in enough chunks. We found the ideal reranker set-up to be 50 chunk input -> 15 output.
What is re-ranking in the context of RAG? Why not just show the code if it’s only 5 lines?
OP. Reranking is a specialized LLM that takes the user query, and a list of candidate results, then re-sets the order based on which ones are more relevant to the query.
If you generate embeddings (of the query, and of the candidate documents) and compare them for similarity, you're essentially asking whether the documents "look like the question."
If you get an LLM to evaluate how well each candidate document follows from the query, you're asking whether the documents "look like an answer to the question."
An ideal candidate chunk/document from a cosine-similarity perspective, would be one that perfectly restates what the user said — whether or not that document actually helps the user. Which can be made to work, if you're e.g. indexing a knowledge base where every KB document is SEO-optimized to embed all pertinent questions a user might ask that "should lead" to that KB document. But for such documents, even matching the user's query text against a "dumb" tf-idf index will surface them. LLMs aren't gaining you any ground here. (As is evident by the fact that webpages SEO-optimized in this way could already be easily surfaced by old-school search engines if you typed such a query into them.)
An ideal candidate chunk/document from a re-ranking LLM's perspective, would be one that an instruction-following LLM (with the whole corpus in its context) would spit out as a response, if it were prompted with the user's query. E.g. if the user asks a question that could be answered with data, a document containing that data would rank highly. And that's exactly the kind of documents we'd like "semantic search" to surface.
I've been thinking about the problem of what to do if the answer to a question is very different to the question itself in embedding space. The KB method sounds interesting and not something I thought about, you sort work on the "document side" I guess. I've also heard of HYDE, the works on the query side, you generate hypothetical answers instead to the user query and look for documents that are similar to the answer, if I've understood it correctly.
The main point didn't get hit on by the responses. Re-ranking is just a mini-LLM (for latency/cost reasons) that does a double heck. Embedding model finds the closest M documents in R^N space. Re-ranker picks the top K documents from the M documents. In theory, if we just used Gemini 2.5 Pro or GPT 5 as the re-ranker, the performance would even be better than whatever small re-ranker people choose to use.
Great read.
But how do people land opportunities to work on exciting project as the author did? I've been trying to get into legal tech in LLM space but I've been unsuccessful.
Anyone here successfully transitioned into legal space? My gut always been legal to the space where LLM can really be useful, the first one is in programming.
Quite a decent hit. Local models don't perform very well in long contexts. We're planning to support a local-only offline set-up for people to host w/o additional dependencies
I find it interesting that so many services and tools were investigated except for embedding models. I would have thought that's one of the biggest levers.
But the model is like 18 months old. and recently we've seen big leaps on MTEB. Not sure how well those translate to reality, but I'm a little surpised this wasn't worth looking into.
we have been trying to make it so that people dont have to reinvent the wheel, over and over and over again, and have a very straight forward all batteries included that can scale to many millions of documents, combining the best of RAG with traditional search and parametric search,
https://docs.mindsdb.com/mindsdb_sql/knowledge_bases/overvie...
Would love your feedback.
I have a RAG setup that doesn't work on documents but other data points that we use for generation (the original data is call recordings but it is heavily processed to just a few text chunks).
Instead of a reranker model we do vector search and then simply ask GPT-5 in an extra call which of the results is the most relevant to the input question. Is there an advantage to actual reranker models rather than using a generic LLM?
I think you should do both in parallel, rather than sequentially. Main reason is vector scoring could cut off something that an LLM will score as relevant
Chunking strategy is a big issue. I found acceptable results by shoving large texts to to gemini flash and have it summarize and extract chunks instead of whatever text splitter I tried. I use the method published by Anthropic https://www.anthropic.com/engineering/contextual-retrieval i.e. include full summary along with chunks for each embedding.
I also created a tool to enable the LLM to do vector search on its own .
I do not use Langchain or python.. I use Clojure+ LLMs' REST APIs.
Really solid write-up — it’s rare to see someone break down the real tradeoffs of scaling RAG beyond the toy examples. The bit about reranking and chunking actually saving more than fancy LLM tricks hits home to me.
You typically add a lot of metadata with each chunk text to be able to filter it, and do to include in the citations. Injecting metadata means that you see what metadata adds helpful context to the LLM, and when you pass the results to the LLM you pass them in a format like this:
It's described in the remainder of the point - they use an LLM to generate additional search queries, either rephrasings of the user's query or bringing additional context from the chat history.
The article raises several interesting points, but I find its claim that Claude Code relies primarily on grep for code search unconvincing. It's clear that Claude Code can parse and reason about code structure, employing techniques far beyond simple regex matching. Since this assumption underpins much of the article's argument, it makes me question the overall reliability of its conclusions a bit.
Or am I completely misunderstanding how Claude Code works?