Postgres is an academic experiment and every time I've seen someone attempt to scale it, it ends in tears.  Salty, salty tears, and massive amounts of un-necessary hardware deployed in an attempt to stop the mysterious bleeding out of its performance under a high rate of queries.  Maybe postgres Jesus will join the org and save it somehow, but he never does.  Anyway, MySQL is better, and lmdb seems best for what nostr is doing (serving notes directly from a memory mapped cache).