Re: Visibility map and hint bits

Merlin Moncure wrote:
> On Thu, May 5, 2011 at 11:59 AM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > There has been a lot of recent discussion about the visibility map (for
> > index-only scans) and hint bits (trying to avoid double-writing a
> > table).
>
> I still think a small tqual.c maintained cache of hint bits will
> effectively eliminate hint bit i/o issues surrounding bulk loads. Tom
> fired a shot across the bow regarding the general worthiness of that
> technique though (see:
> http://postgresql.1045698.n5.nabble.com/Process-local-hint-bit-cache-td4270229.html)
> :(. I can rig up a cleaned up version of the patch pretty
> easily...it's a local change and fairly simple.
>
> I don't think there is any way to remove the hint bits without
> suffering some other problem.

Was that the idea that the pages had to fit in the cache and be updated
with hint bits before being written to disk? Restricting that to the
size of the buffer cache seemed very limiting.

One 8k visibilty map page can hold bits for 1/2 gig of heap pages so I
thought that would be a better all-visible indictor and avoid many
all-visible page writes in bulk load cases.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +