From: Tom Lane <tgl@sss.pgh.pa.us>
To: Aleksander Alekseev <aleksander@timescale.com>
cc: pgsql-hackers <pgsql-hackers@postgresql.org>,
        Marco Slot <marco.slot@gmail.com>, Noah Misch <noah@leadboat.com>,
        Alvaro Herrera <alvherre@alvh.no-ip.org>,
        Christoph Berg <myon@debian.org>,
        Pavan Deolasee <pavan.deolasee@gmail.com>
Subject: Re: Potential ABI breakage in upcoming minor releases
In-reply-to: <CAJ7c6TMCc85YoiSKex5Sztz6bEmV-0YqL7FY=_MxxcyoMGTDfQ@mail.gmail.com>
References: <1976928.1731614974@sss.pgh.pa.us> <202411142033.u6za5a6ylj2k@alvherre.pgsql> <20241114224108.d0.nmisch@google.com> <CAJ7c6TPcUJq_Bwo69f6ysRA1UbmSh_hOOEzJ2EvM0cW=3VEh5w@mail.gmail.com> <CAFMSG9Hy-2-8tfmmKy7noCbA3Yn1UY2SFUwYj7wHODTO8gDm8w@mail.gmail.com> <CAJ7c6TMCc85YoiSKex5Sztz6bEmV-0YqL7FY=_MxxcyoMGTDfQ@mail.gmail.com>
Comments: In-reply-to Aleksander Alekseev <aleksander@timescale.com>
	message dated "Fri, 15 Nov 2024 15:03:21 +0300"
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Date: Fri, 15 Nov 2024 10:09:54 -0500
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Aleksander Alekseev <aleksander@timescale.com> writes:
> Hi Macro,
>> 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.

Yeah, the array-stride problem seems extremely hard to work around,
because whichever size it is, you can't get code compiled with the
other size to work.  I believe ResultRelInfo is the only node type
we use arrays of, so this was a particularly unfortunate place
to break ABI, but there it is.

I'm starting to lean to the opinion that we need a re-wrap.
Given that padding holes exist, the code changes shouldn't
be big.

			regards, tom lane