Re: BUG #16784: Server crash in ExecReScanAgg()

Thank you for the report, Alexander!

On Mon, 2020-12-21 at 14:26 -0500, Tom Lane wrote:
> /* there could be residual pergroup pointers; clear them */
> for (int setoff = 0;
> setoff < aggstate->maxsets + aggstate->num_hashes;
> setoff++)
> aggstate->all_pergroups[setoff] = NULL;
>
> I suspect this is clearing the wrong subset of the all_pergroups
> pointers, but the code is so underdocumented that I'm not very
> sure.

That's correct, but there was a (bad) reason it was done that way that
I had to fix first. A null pergroup was used as a signal not to advance
a group that has spilled, but that's only a good solution for the
hashed grouping sets, not the sorted grouping sets (which is what
caused this bug).

Instead, I solved it by simply not compiling the expressions for the
sorted grouping sets, so that agg_refill_hash_table() can leave those
pergroups alone.

Regards,
Jeff Davis