freeze cannot be finished

Hello!

Could anyone review patch suggested by Jeff Janes ?

Initial thread
http://www.postgresql.org/message-id/flat/1384356585.995240612@f50.i.mail.ru#1384356585.995240612@f50.i.mail.ru

Thanks in advance!

>
> On Wed, Nov 13, 2013 at 3:53 PM, Sergey Burladyan  < eshkinkot@gmail.com > wrote:
> >Jeff Janes < jeff.janes@gmail.com > writes:
> >
> >If I not mistaken, looks like lazy_scan_heap() called from lazy_vacuum_rel()
> >(see [1]) skip pages, even if it run with scan_all == true, lazy_scan_heap()
> >does not increment scanned_pages if lazy_check_needs_freeze() return false, so
> >if this occurred at wraparound vacuum it cannot update pg_class, because
> >pg_class updated via this code:
> >
> >    new_frozen_xid = FreezeLimit;
> >    if (vacrelstats->scanned_pages < vacrelstats->rel_pages)
> >        new_frozen_xid = InvalidTransactionId;
> >
> >    vac_update_relstats(onerel,
> >                        new_rel_pages,
> >                        new_rel_tuples,
> >                        new_rel_allvisible,
> >                        vacrelstats->hasindex,
> >                        new_frozen_xid);
> >
> >so i think in our prevent wraparound vacuum vacrelstats->scanned_pages always
> >less than vacrelstats->rel_pages and pg_class relfrozenxid never updated.
>
> Yeah, I think that that is a bug.  If the clean-up lock is unavailable but the page is inspected without it and found
notto need freezing, then the page needs to be counted as scanned, but is not so counted. 
>
> commit bbb6e559c4ea0fb4c346beda76736451dc24eb4e
> Date:   Mon Nov 7 21:39:40 2011 -0500
>
> But this was introduced in 9.2.0, so unless the OP didn't upgrade to 9.2 until recently, I don't know why it just
startedhappening. 
>
> It looks like a simple fix (to HEAD attached), but I don't know how to test it.
>
> Also, it seem like it might be worth issuing a warning if scan_all is true but all was not scanned.
>
> Cheers,
>
> Jeff
>
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