| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
| Cc: | ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, Gregory Stark <stark(at)enterprisedb(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Peter Eisentraut <peter_e(at)gmx(dot)net>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> |
| Subject: | Re: Visibility map and freezing |
| Date: | 2009-01-20 18:09:18 |
| Message-ID: | 1232474958.2327.200.camel@ebony.2ndQuadrant |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
On Tue, 2009-01-20 at 11:03 +0200, Heikki Linnakangas wrote:
> > - Are there some conditions where whole-table-scanning vacuum is
> more
> > effective than vacuums using visibility map? If so, we should
> switch
> > to full-scan *automatically*, without relying on user
> configurations.
>
> Hmm, the only downside I can see is that skipping a page here and
> there could defeat the OS read-ahead. Perhaps we should call
> posix_fadvise(SEQUENTIAL) to compensate. Or, we could modify the logic
> to only skip pages when there's at least N consecutive pages that can
> be skipped.
I would rather we didn't skip any pages at all unless the gains are
significant. Skipping the odd page makes no difference from a
performance perspective but may have a robustness impact.
"Significant gains" should take into account the size of both heap and
indexes, and recognise that we still scan whole indexes in either case.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Tom Lane | 2009-01-20 18:52:50 | Re: Column-Level Privileges |
| Previous Message | Hiroshi Inoue | 2009-01-20 18:08:38 | Re: Re: [COMMITTERS] pgsql: Explicitly bind gettext() to the UTF8 locale when in use. |