On Thu, Jul 28, 2022 at 7:18 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Wed, Jul 27, 2022 at 8:33 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
>
> > 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.
>
Right, this makes sense. But note that you can no longer have a check
(builder->state == SNAPBUILD_START) which I believe is not required.
We need to do this after restore, in whichever state snapshot was as
any state other than SNAPBUILD_CONSISTENT can have commits without all
their changes.
Accordingly, I think the comment: "Remember the transactions and
subtransactions that were running when xl_running_xacts record that we
decoded first was written." needs to be slightly modified to something
like: "Remember the transactions and subtransactions that were running
when xl_running_xacts record that we decoded was written.". Change
this if it is used at any other place in the patch.
> ---
> + 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.
>
There is no harm in doing that but ideally, that case would have been
covered by an earlier check "if (running->oldestRunningXid ==
running->nextXid)" which suggests "No transactions were running, so we
can jump to consistent."
Kindly make the required changes and submit the back branch patches again.
--
With Regards,
Amit Kapila.