Six Pitfalls Implementing HNSW: A Debug Journal from 0% to 98%+ Recall
While implementing the HNSW algorithm for my vector database project vex (initial code AI-assisted, debugging and optimization done by hand), I ran my first Recall test — every single metric was 0%. Not 50%, not 30%. Zero. The HNSW results and BruteForce results had absolutely no overlap. This post documents the entire journey from 0% to 98%+ recall, cross-referencing each bug with the original HNSW paper.