Two tables. band , and song pointing at it with a foreign key. Four tracks to an EP, twenty million bands, a hundred million rows all told. The most ordinary shape in any schema you have ever worked on. You write the obvious loop, kick it off, go get a coffee. You come back. It's at 4%. Nothing is wrong . No lock. No missing index. No N+1 you can point at in review and feel clever about. The query plan is fine, the code does exactly what it looks like it does, and at the rate it's goin...