c...@anastigmatix.net writes: > And also, isn't it the case that IMMUTABLE should mark a function, > not merely that "doesn't manipulate data", but whose return value > doesn't depend in any way on data (outside its own arguments)?
Right. We can't realistically enforce that either, so it's up to the user. > The practice among PLs of choosing an SPI readonly flag based on > the IMMUTABLE/STABLE/VOLATILE declaration seems to be a sort of > peculiar heuristic, not something inherent in what that declaration > means to the optimizer. (And also influences what snapshot the > function is looking at, and therefore what it can see, which has > also struck me more as a tacked-on effect than something inherent > in the declaration's meaning.) Well, it is a bit odd at first sight, but these properties play together well. See https://www.postgresql.org/docs/current/xfunc-volatility.html regards, tom lane
