Re: Potential ABI breakage in upcoming minor releases - Mailing list pgsql-hackers

Hi Macro,

> I looked a bit at this out of interest. I see an assert failure in the
> lines below when running tests with TimescaleDB compiled against 17.0
> with 17.1 installed. Without the assertion it would anyway segfault
> below.
>
>     /*
>      * Usually, mt_lastResultIndex matches the target rel.  If it happens not
>      * to, we can get the index the hard way with an integer division.
>      */
>     whichrel = mtstate->mt_lastResultIndex;
>     if (resultRelInfo != mtstate->resultRelInfo + whichrel)
>     {
>         whichrel = resultRelInfo - mtstate->resultRelInfo;
>         Assert(whichrel >= 0 && whichrel < mtstate->mt_nrels);
>     }
>
>     updateColnos = (List *) list_nth(node->updateColnosLists, whichrel);
>
> The problem here is that because TimescaleDB compiled against 17.0
> assumes a struct size of 376 (on my laptop) while PostgreSQL allocated
> the array with a struct size of 384, so the pointer math no longer
> holds and the whichrel value becomes nonsense. (1736263376 for
> whatever reason)

Thanks for reporting. Yes, the code assumed fixed
sizeof(ResultRelInfo) within a given PG major release branch which
turned out not to be the case. We will investigate whether it can be
easily fixed on TimescaleDB side.

-- 
Best regards,
Aleksander Alekseev