Thread

Re: Re: [BUG] Incorrect historic snapshot may be serialized to disk during fast-forwarding

Masahiko Sawada <sawada.mshk@gmail.com> — 2025-12-30T01:10:01Z

On Sat, Nov 22, 2025 at 10:33 PM ocean_li_996 <ocean_li_996@163.com> wrote:
>
> Hi ChangAo,
>
> At 2025-11-23 13:31:49, "cca5507" <cca5507@qq.com> wrote:
> >> The patch in attachment is better for me. What do you think?
> >
> >The v2-0001 LGTM.
> >
> >A small suggestion:
> >
> >We should move the 'break' out of the 'if', because we don't want it fall through to XLOG_HEAP2_REWRITE if we are fast-forwarding.
>
> Fair. The patch updated is provided in attachment.
>

While I agree with your analysis, I'm not sure what actual problems it
could lead to in practice. Have you had a chance to reproduce this
behavior by using DDLs instead of a user-catalog table? IIUC the
problem can occur if a transaction makes catalog changes and writes
only NEW_CID WAL records without INVALIDATION WAL records. However,
I'm not sure there are such transactions in practice. IIUC it would
not be a problem in terms of logical decoding even if we don't include
their XIDs to the snapshot if they change only user-catalog tables. It
might be more future proof to mark transactions as catalog-changed
even when fast-forwarding a NEW_CID record, as you proposed, but I'd
like to confirm the actual problems first.

Regards,

-- 
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com