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Dev.to
Dev.to
6/27/2026
The original title is "Building a RAG System from Scratch — Design Decisions Explained"

The original title is "Building a RAG System from Scratch — Design Decisions Explained"

Original: Building a RAG System from Scratch — Design Decisions Explained

Short summary

Explains key RAG architecture decisions: pgvector + PostgreSQL is cost-effective for most use cases, 768-dimensional embeddings balance quality and cost, asymmetric task types improve retrieval accuracy, and HNSW indexing handles production scale. Includes four-phase scaling strategy and guidance on when to upgrade embedding vs. generation models.

  • pgvector integrates with PostgreSQL, scales to millions of documents, cheaper than purpose-built vector DBs for most teams
  • 768-dimension embeddings are the production sweet spot—full quality with faster index builds and lower storage costs
  • Use different task types for ingestion and querying to leverage asymmetric model training and improve accuracy

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