Re: Block-level CRC checks

pgsql@mohawksoft.com writes:
>> 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).

Your optimism is showing ;-).  XLogInsert routinely shows up as a major
CPU hog in any update-intensive test, and AFAICT that's mostly from the
CRC calculation for WAL records.

We could possibly use something cheaper than a real CRC, though.  A
word-wide XOR (ie, effectively a parity calculation) would be sufficient
to detect most problems.
        regards, tom lane