I found this unhelpful, sorry. "Faster vector calculations" sounds like a faster way to add or multiply vectors, which TTBOMK k-means doesn't help with at all. There are hundreds of types of things called an "index"; I'm familiar with ordinary RDBMS indices but haven't heard of ivfflat or prism indices. Gemini tells me PostgreSQL uses them to support approximate nearest neighbour queries on geometric data -- e.g., finding the nearest train station to your current position.