Advanced RAG Techniques Aren't Better. They're Better Sometimes.

Advanced RAG techniques are not free upgrades. They are tools with trade-offs.

I added five retrieval techniques to a RAG pipeline to test them. The most important result was the technique that failed.

I expected HyDE to improve retrieval. Instead, it backfired on certain queries. Recall dropped from 0.80 to 0.17. The technique did not just fail to help. It actively pulled the wrong data into the results.

Every advanced technique I tested works like this:

  • Hybrid search (BM25 + dense): Great for exact terms. Use it when your query relies on specific parameters.
  • HyDE: Great for casual questions that do not match document vocabulary. It fails when the query already matches the corpus well.
  • Reranking: Great when the right chunk is in the results but sits too low in the list.
  • Contextual retrieval: Great for short chunks that lack context. It adds cost because you must use an LLM for every chunk.

I built this pipeline using Anthropic documentation. I used Postgres with pgvector and an HNSW index. I treated this like a backend engineer. I did not ask if a technique was state of the art. I asked if it earned its complexity.

Every component you add is something you must operate, debug, and pay for.

Before adding complex tools, I measured a baseline using plain dense retrieval.

The results showed two different metrics:

  • Faithfulness: 0.96
  • Context precision: 0.60

This data changed my entire approach. Most techniques target retrieval. My retrieval was the failing part. If faithfulness was low, I would have tuned prompts. Since retrieval was low, I had to tune the search.

I also learned a lesson about evaluation tools. I tried using Ragas, but it was too slow. It would retry failed calls and take hours. I built my own async harness instead. I ran the same metrics in 221 seconds instead of 11 hours.

The takeaway is simple:

Do not apply techniques blindly. Use a query router to pick the right mode for the right question. Measure your data first. Then pick the tool that solves your specific failure mode.

The model is new. The engineering discipline is not.

Source: https://dev.to/yogesh23012001/advanced-rag-techniques-arent-better-theyre-better-sometimes-4m2o