A uuid primary key: 172 seconds against 59
16 bytes against 8 is 40 percent more index. Arrival order adds another 23 percent on top of that, plus 3 times the insert time once the index outgrows shared_buffers.
Writing
Money in a double: 4.35 * 100 comes out 434
4 prices in every 100 are exact doubles. Across a million amounts the wrong kopeck only ever turned up on an exact half: 3656 of them at 18 percent, none at 20.
Reading UTF-8 as 1251: "Привет"
Mojibake is deterministic. 6 letters, 12 bytes and 5 code pages, plus a byte table that tells you which pair of encodings collided.