| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Simon Riggs <simon(dot)riggs(at)2ndquadrant(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Simon Riggs <simon(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Peter Eisentraut <peter_e(at)gmx(dot)net> |
| Subject: | Re: Turning off HOT/Cleanup sometimes |
| Date: | 2015-04-22 16:16:43 |
| Message-ID: | 20150422161643.GB13362@momjian.us |
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| Lists: | pgsql-hackers |
On Tue, Apr 21, 2015 at 04:36:53PM -0400, Robert Haas wrote:
> > Keep in mind there's a disconnect between dirtying a page and writing it
> > to storage. A page could remain dirty for a long time in the buffer
> > cache. This writing of sequential pages would occur at checkpoint time
> > only, which seems the wrong thing to optimize. If some other process
> > needs to evict pages to make room to read some other page in, surely
> > it's going to try one page at a time, not write "many sequential dirty
> > pages."
>
> Well, for a big sequential scan, we use a ring buffer, so we will
> typically be evicting the pages that we ourselves read in moments
> before. So in this case we would do a lot of sequential writes of
> dirty pages.
Ah, yes, this again supports the prune-then-skip approach, rather than
doing the first X% pruneable pages seen.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ Everyone has their own god. +
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