| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
| Cc: | Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, Andres Freund <andres(at)anarazel(dot)de>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, David Steele <david(at)pgmasters(dot)net>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, "Ideriha, Takeshi" <ideriha(dot)takeshi(at)jp(dot)fujitsu(dot)com>, PostgreSQL-Dev <pgsql-hackers(at)postgresql(dot)org>, Kuntal Ghosh <kuntalghosh(dot)2007(at)gmail(dot)com> |
| Subject: | Re: GUC for cleanup indexes threshold. |
| Date: | 2017-09-19 23:55:38 |
| Message-ID: | CAH2-Wzn0-3zxGRp_qp1OaEXY7h1W0-W_VCFO0nDv0K_+kabyYQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Sep 19, 2017 at 4:47 PM, Claudio Freire <klaussfreire(at)gmail(dot)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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