On Thursday, October 14, 2021 11:21 AM Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote:
> At Mon, 11 Oct 2021 15:27:41 +0900, Masahiko Sawada
> <sawada.mshk@gmail.com> wrote in
> >
> > On Fri, Oct 8, 2021 at 4:50 PM Kyotaro Horiguchi
> > <horikyota.ntt@gmail.com> wrote:
> > > I came up with the third way. SnapBuildCommitTxn already properly
> > > handles the case where a ReorderBufferTXN with
> > > RBTXN_HAS_CATALOG_CHANGES. So this issue can be resolved by
> create
> > > such ReorderBufferTXNs in SnapBuildProcessRunningXacts.
> >
> > Thank you for the idea and patch!
> >
> > It's much simpler than mine. I think that creating an entry of a
> > catalog-changed transaction in the reorder buffer before
> > SunapBuildCommitTxn() is the right direction.
> >
> > After more thought, given DDLs are not likely to happen than DML in
> > practice, probably we can always mark both the top transaction and its
> > subtransactions as containing catalog changes if the commit record has
> > XACT_XINFO_HAS_INVALS? I believe this is not likely to lead to
> > overhead in practice. That way, the patch could be more simple and
> > doesn't need the change of AssertTXNLsnOrder().
> >
> > I've attached another PoC patch. Also, I've added the tests for this
> > issue in test_decoding.
>
> Thanks for the test script. (I did that with TAP framework but isolation tester
> version is simpler.)
>
> It adds a call to ReorderBufferAssignChild but usually subtransactions are
> assigned to top level elsewherae. Addition to that
> ReorderBufferCommitChild() called just later does the same thing. We are
> adding the third call to the same function, which looks a bit odd.
It can be odd. However, we
have a check at the top of ReorderBufferAssignChild
to judge if the sub transaction is already associated or not
and skip the processings if it is.
> And I'm not sure it is wise to mark all subtransactions as "catalog changed"
> always when the top transaction is XACT_XINFO_HAS_INVALS.
In order to avoid this,
can't we have a new flag (for example, in reorderbuffer struct) to check
if we start decoding from RUNNING_XACTS, which is similar to the first patch of [1]
and use it at DecodeCommit ? This still leads to some extra specific codes added
to DecodeCommit and this solution becomes a bit similar to other previous patches though.
[1] - https://www.postgresql.org/message-id/81D0D8B0-E7C4-4999-B616-1E5004DBDCD2%40amazon.com
Best Regards,
Takamichi Osumi