On Tue, Sep 21, 2021 at 9:42 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
> On Tue, Sep 21, 2021 at 4:29 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > Some more comments,
> >
> > In pgoutput_row_filter_update(), first, we are deforming the tuple in
> > local datum, then modifying the tuple, and then reforming the tuple.
> > I think we can surely do better here. Currently, you are reforming
> > the tuple so that you can store it in the scan slot by calling
> > ExecStoreHeapTuple which will be used for expression evaluation.
> > Instead of that what you need to do is to deform the tuple using
> > tts_values of the scan slot and later call ExecStoreVirtualTuple(), so
> > advantages are 1) you don't need to reform the tuple 2) the expression
> > evaluation machinery doesn't need to deform again for fetching the
> > value of the attribute, instead it can directly get from the value
> > from the virtual tuple.
> >
>
> I have one more question, while looking into the
> ExtractReplicaIdentity() function, it seems that if any of the "rep
> ident key" fields is changed then we will write all the key fields in
> the WAL as part of the old tuple, not just the changed fields. That
> means either the old tuple will be NULL or it will be having all the
> key attributes. So if we are supporting filter only on the "rep ident
> key fields" then is there any need to copy the fields from the new
> tuple to the old tuple?
>
Yes, I just figured this out while testing. So we don't need to copy fields
from the new tuple to the old tuple.
But there is still the case of your fix for the unchanged toasted RI
key fields in the new tuple
which needs to be copied from the old tuple to the new tuple. This
particular case
seems to violate both rules that an old tuple will be present only
when there are changed
RI key fields and that if there is an old tuple it will contain all RI
key fields. I think we
still need to deform both old tuple and new tuple, just to handle this case.
There is currently logic in ReorderBufferToastReplace() which already
deforms the new tuple
to detoast changed toasted fields in the new tuple. I think if we can
enhance this logic for our
purpose, then we can avoid an extra deform of the new tuple.
But I think you had earlier indicated that having untoasted unchanged
values in the new tuple
can be bothersome.
Any suggestions?
regards,
Ajin Cherian
Fujitsu Australia
regards,
Ajin Cherian
Fujitsu Australia