On 2011-12-19 02:55, Greg Stark wrote:
On Sun, Dec 18, 2011 at 7:51 PM, Jesper Krogh<jes...@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
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Jesper
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