Re: logical streaming of xacts via test_decoding is broken

On Mon, Nov 9, 2020 at 11:21 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Mon, Nov 9, 2020 at 11:04 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> >
> > On Mon, Nov 9, 2020 at 11:00 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > > Michael reported a BF failure [1] related to one of the logical
> > > streaming test case and I've analyzed the issue. As responded on
> > > pgsql-committers [2], the issue here is that the streaming
> > > transactions can be interleaved and because we are maintaining whether
> > > xact_wrote_changes at the LogicalDecodingContext level, one of later
> > > transaction can overwrite the flag for previously streaming
> > > transaction. I think it is logical to have this flag at each
> > > transaction level (aka in ReorderBufferTxn), however till now it was
> > > fine because the changes of each transaction are decoded at one-shot
> > > which will be no longer true. We can keep a output_plugin_private data
> > > pointer in ReorderBufferTxn which will be used by test_decoding module
> > > to keep this and any other such flags in future. We need to set this
> > > flag at begin_cb and stream_start_cb APIs and then reset/remove it at
> > > stream_commit_cb, stream_abort_cb and stream_stop_cb APIs.
>
> So IIUC, we need to keep 'output_plugin_private' in
> LogicalDecodingContext as well as in ReorderBufferTxn, So the
> output_plugin_private in the ReorderBufferTxn will currently just keep
> one flag xact_wrote_changes and the remaining things will still be
> maintained in output_plugin_private of the LogicalDecodingContext. Is
> my understanding correct?
>

Yes. But keep it as void * so that we can add more things later if required.

--
With Regards,
Amit Kapila.