Re: [BUG]Update Toast data failure in logical replication

On Thu, Jul 22, 2021 at 4:11 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Thu, Jun 3, 2021 at 5:15 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> >
> > On Wed, Jun 2, 2021 at 7:23 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > >
> > > On Wed, Jun 2, 2021 at 7:20 PM Kuntal Ghosh <kuntalghosh.2007@gmail.com> wrote:
> > > >
> > > > On Wed, Jun 2, 2021 at 3:10 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > > > >
> > > > > Yes, you are right.  I will change it in the next version, along with
> > > > > the test case.
> > > > >
> > > > +    /*
> > > > +     * if the key hasn't changed and we're only logging the key, we're done.
> > > > +     * But if tuple has external data then we might have to detoast the key.
> > > > +     */
> > > > This doesn't really mention why we need to detoast the key even when
> > > > the key remains the same. I guess we can add some more details here.
> > >
> > > Noted, let's see what others have to say about fixing this, then I
> > > will fix this along with one other pending comment and I will also add
> > > the test case.  Thanks for looking into this.
> >
> > I have fixed all the pending issues, I see there is already a test
> > case for this so I have changed the output for that.
> >
>
> IIUC, this issue occurs because we don't log the actual key value for
> unchanged toast key. It is neither logged as part of old_key_tuple nor
> for new tuple due to which we are not able to find it in the
> apply-side when we searched it via FindReplTupleInLocalRel. Now, I
> think it will work if we LOG the entire unchanged toasted value as you
> have done in the patch but can we explore some other way to fix it. In
> the subscriber-side, can we detect that the key column has toasted
> value in the new tuple and try to first fetch it and then do the index
> search for the fetched toasted value? I am not sure about the
> feasibility of this but wanted to see if we can someway avoid logging
> unchanged toasted key value as that might save us from additional WAL.

Yeah if we can do this then it will be a better approach, I think as
you mentioned we can avoid logging unchanged toast key data.  I will
investigate this next week and update the thread.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com