Re: [BUG] Logical replication failure "ERROR: could not map filenode "base/13237/442428" to relation OID" with catalog modifying txns

On Wed, Jul 27, 2022 at 8:33 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Mon, Jul 25, 2022 at 11:26 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > On Mon, Jul 25, 2022 at 10:45 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > I've attached the patch for REl15 that I forgot.
> >
>
> I feel the place to remember running xacts information in
> SnapBuildProcessRunningXacts is not appropriate. Because in cases
> where there are no running xacts or when xl_running_xact is old enough
> that we can't use it, we don't need that information. I feel we need
> it only when we have to reuse the already serialized snapshot, so,
> won't it be better to initialize at that place in
> SnapBuildFindSnapshot()?

Good point, agreed.

> I have changed accordingly in the attached
> and apart from that slightly modified the comments and commit message.
> Do let me know what you think of the attached?

It would be better to remember the initial running xacts after
SnapBuildRestore() returns true? Because otherwise, we could end up
allocating InitialRunningXacts multiple times while leaking the old
ones if there are no serialized snapshots that we are interested in.

---
+ if (builder->state == SNAPBUILD_START)
+ {
+ int nxacts =
running->subxcnt + running->xcnt;
+ Size sz = sizeof(TransactionId) * nxacts;
+
+ NInitialRunningXacts = nxacts;
+ InitialRunningXacts =
MemoryContextAlloc(builder->context, sz);
+ memcpy(InitialRunningXacts, running->xids, sz);
+ qsort(InitialRunningXacts, nxacts,
sizeof(TransactionId), xidComparator);
+ }

We should allocate the memory for InitialRunningXacts only when
(running->subxcnt + running->xcnt) > 0.

Regards,

--
Masahiko Sawada
EDB: https://www.enterprisedb.com/