Re: BUG #16122: segfault pg_detoast_datum (datum=0x0) at fmgr.c:1833 numrange query

Thank you Michael!  I know this is a late response but didn't want to
clutter the message stream until we had confirmation, but I applied this
patch to our server and could not replicate the bug.  So this patch is
working for us presently.

Thanks again Michael,
Adam


On Mon, Dec 9, 2019 at 9:38 PM Michael Paquier <michael@paquier.xyz> wrote:

> On Tue, Nov 19, 2019 at 08:40:56PM +0900, Michael Paquier wrote:
> > If you add an ANALYZE on the table natica_hdu_test after restoring, I
> > am rather sure that you would reproduce the crash more quickly because
> > the handling around the stats of the column are busted here.  Anyway,
> > taking my example of upthread, I have been also able to reproduce the
> > problem on REL_10_STABLE even with assertions enabled: the trick is
> > that you need to leave once the session after the analyze on the
> > table.  Then a SELECT within a new session is enough to crash the
> > server.
>
> So...  I have looked more at this one, and from my previous example it
> seems that we have a one-off error when looking up at the array
> holding the histograms for ranges (lower and upper bound).
>
> In my previous example, we get to build 101 RangeBounds when beginning
> to calculate the range operator selectivity in
> calc_hist_selectivity().  However, when we get to the point of
> calc_hist_selectivity_contained(), upper_index gets calculated at 100
> which is just at the limit of the indexed bounds, and the code would
> happily look at the last bound as well as the one-after-the-last bound
> as range_cmp_bounds() sees fit, but the latter just points to the
> void.  The code looks wrong since its introduction in 59d0bf9d and
> it seems that the changes done for free_attstatsslot() in 9aab83f make
> the issue more easily reproducible.
>
> A fix like the rough POC attached addresses the issue, but I think
> that's too naive to not count for the first bin in the ranges
> evaluated.  Tomas, you may be more familiar with this area of the code
> than I am.  What do you think?
> --
> Michael
>