Re: Wrong results from Parallel Hash Full Join

Hi,

On 2023-04-12 10:57:17 -0400, Melanie Plageman wrote:
> HeapTupleHeaderHasMatch() checks if HEAP_TUPLE_HAS_MATCH is set.
>
> In htup_details.h, you will see that HEAP_TUPLE_HAS_MATCH is defined as
> HEAP_ONLY_TUPLE
> /*
> * HEAP_TUPLE_HAS_MATCH is a temporary flag used during hash joins. It is
> * only used in tuples that are in the hash table, and those don't need
> * any visibility information, so we can overlay it on a visibility flag
> * instead of using up a dedicated bit.
> */
> #define HEAP_TUPLE_HAS_MATCH HEAP_ONLY_TUPLE /* tuple has a join match */
>
> If you redefine HEAP_TUPLE_HAS_MATCH as something that isn't already
> used, say 0x1800, the query returns correct results.
> [...]
> The question is, why does this only happen for a parallel full hash join?

I'd guess that PHJ code is missing a HeapTupleHeaderClearMatch() somewhere,
but the non-parallel case isn't.

Greetings,

Andres Freund