> maintenance_work_mem begs to differ.

HNSW indices are big. Let's suppose I have an HNSW index which fits in a few hundred gigabytes of memory, or perhaps a few terabytes. How do I reasonably rebuild this using maintenance_work_mem? Double the size of my database for a week? What about the knock-on impacts on the performance for the rest of my database-stuff - presumably I'm relying on this memory for shared_buffers and caching? This seems like the type of workload that is being discussed here, not a toy 20GB index or something.

> You use REINDEX CONCURRENTLY.

Even with a bunch of worker processes, how do I do this within a reasonable timeframe?

> How do you think a B+tree gets updated?

Sure, the computational complexity of insertion into an HNSW index is sublinear, the constant factors are significant and do actually add up. That being said, I do find this the weakest of the author's arguments.