> Hannu Krosing <hannu@2ndQuadrant.com> writes:
>> So I don't think that this is a space issue.
>
> No, it's all about time penalties and loss of concurrency.
I don't think that the amount of time it would take to calculate and test
the sum is even important. It may be in older CPUs, but these days CPUs
are so fast in RAM and a block is very small. On x86 systems, depending on
page alignment, we are talking about two or three pages that will be "in
memory" (They were used to read the block from disk or previously
accessed).