Re: Parallel Append subplan order instability on aye-aye

Hi,

On 2019-07-15 21:12:32 -0400, Tom Lane wrote:
> But I bet that these tables forming
> an inheritance hierarchy (with multiple inheritance even) does
> have something to do with it somehow, because if this were a
> generic VACUUM bug surely we'd be seeing it elsewhere.

It's possible that it's hidden in other cases, because of

void
table_block_relation_estimate_size(Relation rel, int32 *attr_widths,
BlockNumber *pages, double *tuples,
double *allvisfrac,
Size overhead_bytes_per_tuple,
Size usable_bytes_per_page)
...
* If the table has inheritance children, we don't apply this heuristic.
* Totally empty parent tables are quite common, so we should be willing
* to believe that they are empty.
*/
if (curpages < 10 &&
relpages == 0 &&
!rel->rd_rel->relhassubclass)
curpages = 10;

which'd not make us actually take a relpages=0 into account for tables
without inheritance. A lot of these tables never get 10+ pages long, so
the heuristic would always apply...

Greetings,

Andres Freund