Writes in postgres touch all indexes. When you index every column, you have to touch every column's index for every write. Writes in MySQL (using InnoDB) just

Writes in postgres touch all indexes. When you index every column, you have to touch every column's index for every write. Writes in MySQL (using InnoDB) just touch the pkey index, to which all other indexes point, or something like that. (Can someone who knows MySQL innards better — I avoid it like it's contagious — please confirm or clarify?)