Re: What is an 'unused item pointer'

On Sun, Sep 25, 2005 at 12:09:24AM -0400, Tom Lane wrote:
> "Jim C. Nasby" <jnasby@pervasive.com> writes:
> > On Sat, Sep 24, 2005 at 07:19:10PM -0400, Tom Lane wrote:
> >> Currently, when a tuple is reclaimed by VACUUM, we just mark its item
> >> pointer as unused (and hence recyclable).  I think it might be safe to
> >> decrease pd_lower if there are unused pointers at the end of the page's
> >> pointer array, but we don't currently do that.
>
> > Sounds like a good newbie TODO?
>
> Uh, no, because the $64 question is whether it actually *is* safe, or
> perhaps would be safe with more locking than we do now.  I'm not sure of
> the answer myself, and would have zero confidence in a newbie's answer.
>
> Decreasing pd_lower would definitely be a win if we can do it free or
> cheaply.  If it requires significant additional locking overhead, then
> maybe not.

Ok, sounds like a non-newbie TODO then. :)
--
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
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