Field Notes
Reading an explain plan with the product owner in the room
Why we invite non-engineers into query reviews, and which parts of an explain plan they actually need to see.
Explain plans intimidate people who do not write SQL daily. That is fine. Product owners still need to understand why a screen feels slow and what trade-offs a rewrite creates. In our query performance reviews we translate three ideas only: which table is scanned, which join multiplies rows, and which filter arrives too late.
We avoid dumping the entire plan on a projector. Instead we sketch the hot path on a whiteboard, mark the expensive node, and ask the product owner whether the business rule that forces that join still holds. Often the “performance problem” is a rule that should have been denormalized into a read model months earlier.
Bring the person who owns the deadline into the first review hour. The second hour can stay with engineers for index syntax. The shared hour is where budgets get decided without another week of private debate.