Re: [HACKERS] GUC for cleanup indexes threshold.

On Tue, Sep 19, 2017 at 4:47 PM, Claudio Freire <klaussfreire@gmail.com> wrote:
> Maybe this is looking at the problem from the wrong direction.
>
> Why can't the page be added to the FSM immediately and the check be
> done at runtime when looking for a reusable page?
>
> Index FSMs currently store only 0 or 255, couldn't they store 128 for
> half-recyclable pages and make the caller re-check reusability before
> using it?

No, because it's impossible for them to know whether or not the page
that their index scan just landed on recycled just a second ago, or
was like this since before their xact began/snapshot was acquired.

For your reference, this RecentGlobalXmin interlock stuff is what
Lanin & Shasha call "The Drain Technique" within "2.5 Freeing Empty
Nodes". Seems pretty hard to do it any other way.

-- 
Peter Geoghegan


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