EXPLAIN shows gross problems. There are plenty of things well under an order of magnitude that won’t necessarily show up. It’s a very coarse grained yardstick. If you think it’s the only yardstick that matters, then you and I probably disagree about a great number of other things too.
EXPLAIN shows you how the query is being executed.
It won't always give you a recipe for a solution but it's always useful for an experienced Postgres developer to look at to understand why it isn't performing like you expect.
I still don't understand why the two queries runs faster than a single query. There might be good reasons for that and they might not be able to be fixed but at the same time there might be ways to fix it. EXPLAIN gives you clues.
Comments
EXPLAIN shows gross problems. There are plenty of things well under an order of magnitude that won’t necessarily show up. It’s a very coarse grained yardstick. If you think it’s the only yardstick that matters, then you and I probably disagree about a great number of other things too.
EXPLAIN shows you how the query is being executed.
It won't always give you a recipe for a solution but it's always useful for an experienced Postgres developer to look at to understand why it isn't performing like you expect.
I still don't understand why the two queries runs faster than a single query. There might be good reasons for that and they might not be able to be fixed but at the same time there might be ways to fix it. EXPLAIN gives you clues.