Re: Block-level CRC checks

On Wed, Oct 1, 2008 at 10:27 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> 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.

I probably wouldn't compare checksumming *every* WAL record to a
single block-level checksum.

-- 
Jonah H. Harris, Senior DBA
myYearbook.com