Re: free space map and visibility map

On Fri, Mar 17, 2017 at 9:37 PM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> With some intensive crash-recovery testing, I've run into a situation where
> I get some bad table bloat. There will be large swaths of the table which
> are empty (all results from heap_page_items other than lp are either zero or
> NULL), but have zero available space in the fsm, and are marked as
> all-visible and all-frozen in the vm.
>
> I guess it is a result of a crash causing updates to the fsm to be lost.
> Then due to the (crash-recovered) visibility map showing them as all visible
> and all frozen, vacuum never touches the pages again, so the fsm never gets
> corrected.

I guess that this happens only if heap_xlog_clean applies FPI. Right?
Updating fsm can be lost but fsm is updated by replaying HEAP2_CLEAN
record during crash recovery.

>
> 'VACUUM (DISABLE_PAGE_SKIPPING) foo;' does fix it, but that seems to be
> the only thing that will.

If the above is correct, another one option is to allow
heap_xlog_clean to update fsm even when appling FPI.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center