Re: Skipping logical replication transactions on subscriber side

On Wed, Aug 18, 2021 at 3:33 PM houzj(dot)fnst(at)fujitsu(dot)com
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> On Tues, Aug 17, 2021 1:01 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > On Mon, Aug 16, 2021 at 3:59 PM houzj(dot)fnst(at)fujitsu(dot)com <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> > > 3)
> > > Do we need to invoke set_apply_error_context_xact() in the function
> > > apply_handle_stream_prepare() to save the xid and timestamp ?
> >
> > Yes. I think that v8-0001 patch already set xid and timestamp just after parsing
> > stream_prepare message. You meant it's not necessary?
>
> Sorry, I thought of something wrong, please ignore the above comment.
>
> >
> > I'll submit the updated patches soon.
>
> I was thinking about the place to set the errcallback.callback.
>
> apply_dispatch(StringInfo s)
> {
> LogicalRepMsgType action = pq_getmsgbyte(s);
> + ErrorContextCallback errcallback;
> + bool set_callback = false;
> +
> + /*
> + * Push apply error context callback if not yet. Other fields will be
> + * filled during applying the change. Since this function can be called
> + * recursively when applying spooled changes, we set the callback only
> + * once.
> + */
> + if (apply_error_callback_arg.command == 0)
> + {
> + errcallback.callback = apply_error_callback;
> + errcallback.previous = error_context_stack;
> + error_context_stack = &errcallback;
> + set_callback = true;
> + }
> ...
> + /* Pop the error context stack */
> + if (set_callback)
> + error_context_stack = errcallback.previous;
>
> It seems we can put the above code in the function LogicalRepApplyLoop()
> around invoking apply_dispatch(), and in that approach we don't need to worry
> about the recursively case. What do you think ?

Thank you for the comment!

I think you're right. Maybe we can set the callback before entering to
the main loop and pop it after breaking from it. It would also fix the
problem reported by Tang[1]. But one thing we need to note that since
we want to reset apply_error_callback_arg.command at the end of
apply_dispatch() (otherwise we could end up setting the apply error
context to an irrelevant error such as network error), when
apply_dispatch() is called recursively probably we need to save the
apply_error_callback_arg.command before setting the new command and
then revert back to the saved command. Is that right?

Regards,

[1] https://www.postgresql.org/message-id/OS0PR01MB6113E5BC24922A2D05D16051FBFE9%40OS0PR01MB6113.jpnprd01.prod.outlook.com

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