On 2014-12-18 16:05:23 -0600, Jim Nasby wrote:
> On 12/18/14, 3:02 PM, Alvaro Herrera wrote:
> >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?
>
> I would prefer that we at least count if we initially don't get the lock;
> presumably that number is always low anyway and in that case I think we're
> done with this. If it turns out it is common to initially miss the pin then
> we could do something fancier.
>
> So how about if in the scan_all case we say something like "unable to
> initially acquire pin on %d buffers\n"?
I'd just do away with the difference between scan_all/!scan_all and
always say the above.
Greetings,
Andres Freund
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Andres Freund http://www.2ndQuadrant.com/
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