| From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Proposal: Log inability to lock pages during vacuum |
| Date: | 2014-12-18 21:02:54 |
| Message-ID: | 20141218210254.GQ1768@alvh.no-ip.org |
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| Thread: | |
| Lists: | pgsql-hackers |
Andres Freund wrote:
> On 2014-12-18 16:41:04 -0300, Alvaro Herrera wrote:
> > + if (scan_all)
> > + appendStringInfo(&buf, _("waited for %d buffer pins\n"),
> > + vacrelstats->pinned_pages);
> > + else
> > + appendStringInfo(&buf,
> > + _("skipped %d pages due to buffer pins\n"),
> > + vacrelstats->pinned_pages);
>
> Unless I miss something this is, as mentioned before, not
> correct. scan_all doesn't imply at all that we waited for buffer
> pins. We only do so if lazy_check_needs_freeze(buf). Which usually won't
> be true for a *significant* number of pages.
Ah, interesting, I didn't remember we had that. I guess one possible
tweak is to discount the pages we skip from pinned_pages; or we could
keep a separate count of pages waited for. Jim, up for a patch?
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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