Re: BUG #18280: logical decoding build wrong snapshot for subtransactions

Thank you for your attention.

> On Jan 23, 2024, at 19:42, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Wed, Jan 10, 2024 at 7:56 PM feichanghong <feichanghong(at)qq(dot)com> wrote:
>>
>>> SnapBuildXidSetCatalogChanges (introduced in 272248a) skipping the check for
>>> the sub-transactions when the parent transaction has been marked as
>>> containing catalog changes should be the root cause of the problem.
>>
>> My fix is to remove the ReorderBufferXidHasCatalogChanges condition from the SnapBuildXidSetCatalogChanges function. This approach has a false positive; the subtransactions that didn't change catalog to the snapshot are also added to the commit list. But that won't be a problem since we use snapshot built during decoding only to read system catalogs, as 272248a's commit message says.
>>
>
> Thanks, your analysis sounds correct to me. BTW, I think this should
> occur only in 15 and 14 because in prior branches we didn't check if
> the xact has catalog changes before marking its subxacts. From 16
> onwards, we already accurately serialize the xacts and subxacts that
> have made any catalog changes, so this problem shouldn't be there. Can
> you please once verify the same?
>
Yes, I verified versions 11 to 16 one by one, and this problem only occurs
in 14 and 15.

Best Regards,
Fei Changhong
Alibaba Cloud Computing Ltd.