Re: Page Checksums

On 2011-12-19 02:55, Greg Stark wrote:
> On Sun, Dec 18, 2011 at 7:51 PM, Jesper Krogh<jesper@krogh.cc>  wrote:
>> I dont know if it would be seen as a "half baked feature".. or similar,
>> and I dont know if the hint bit problem is solvable at all, but I could
>> easily imagine checksumming just "skipping" the hit bit entirely.
> That was one approach discussed. The problem is that the hint bits are
> currently in each heap tuple header which means the checksum code
> would have to know a fair bit about the structure of the page format.
> Also the closer people looked the more hint bits kept turning up
> because the coding pattern had been copied to other places (the page
> header has one, and index pointers have a hint bit indicating that the
> target tuple is deleted, etc). And to make matters worse skipping
> individual bits in varying places quickly becomes a big consumer of
> cpu time since it means injecting logic into each iteration of the
> checksum loop to mask out the bits.
I do know it is a valid and really relevant point (the cpu-time spend),
but here in late 2011 it is really a damn irritating limitation, since if
there any resources I have plenty available of in the production environment
then it is cpu-time, just not on the "single core currently serving the 
client".

Jesper
-- 
Jesper