RE: Rework LogicalOutputPluginWriterUpdateProgress

On Friday, March 3, 2023 8:18 AM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> On Wed, Mar 1, 2023 at 9:16 PM wangw(dot)fnst(at)fujitsu(dot)com
> <wangw(dot)fnst(at)fujitsu(dot)com> wrote:
> >
> > On Tues, Feb 28, 2023 at 9:12 AM Peter Smith <smithpb2250(at)gmail(dot)com>
> wrote:
> > > Here are some comments for the v2-0001 patch.
> > >
> > > (I haven't looked at the v3 that was posted overnight; maybe some of
> > > my comments have already been addressed.)
> >
> > Thanks for your comments.
> >
> > > ======
> > > General
> > >
> > > 1. (Info from the commit message)
> > > Since we can know whether the change is an end of transaction change
> > > in the common code, we removed the
> LogicalDecodingContext->end_xact
> > > introduced in commit f95d53e.
> > >
> > > ~
> > >
> > > TBH, it was not clear to me that this change was an improvement.
> > > IIUC, it removes the "unnecessary" member, but only does that by
> > > replacing it everywhere with a boolean parameter passed to
> > > update_progress_and_keepalive(). So the end result seems no less
> > > code, but it is less readable code now because you need to know what
> > > the true/false parameter means. I wonder if it would have been
> > > better just to leave this how it was.
> >
> > Since I think we can know the meaning of the input based on the
> > parameter name of the function, I think both approaches are fine. But
> > the approach in the current patch can reduce a member of the
> > structure, so I think this modification looks good to me.
> >
>
...
>
> Anyway, I think this exposes another problem. If you still want the patch to pass
> the 'finshed_xact' parameter separately then AFAICT the first parameter (ctx)
> now becomes unused/redundant in the WalSndUpdateProgressAndKeepalive
> function, so it ought to be removed.
>

I am not sure about this. The first parameter (ctx) has been introduced since
the Lag tracking feature. I think this is to make it consistent with other
LogicalOutputPluginWriter callbacks. In addition, this is a public callback
function and user can implement their own logic in this callbacks based on
interface, removing this existing parameter doesn't look great to me. Although
this patch also removes the existing skipped_xact, but it's because we decide
to use another parameter did_write which can play a similar role.

Best Regards,
Hou zj