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"?
(Happy to do the patch either way, but I'd like us to decide what we're doing
first. ;)
--
Jim Nasby, Data Architect, Blue Treble Consulting
Data in Trouble? Get it in Treble! http://BlueTreble.com
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