Re: Block-level CRC checks

On Wednesday 01 October 2008 10:27:52 Tom Lane wrote:
> pgsql(at)mohawksoft(dot)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.
>

Yeah... for those who run on filesystems that do checksumming for you, I'd bet
they'd much rather see time spent in turning that off rather than
checksumming everything else. (just guessing)

--
Robert Treat
Build A Brighter LAMP :: Linux Apache {middleware} PostgreSQL