Re: row filtering for logical replication

On Mon, Jan 24, 2022 at 2:47 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> > (3) pgoutput_row_filter_exec_expr
> > pgoutput_row_filter_exec_expr() returns false if "isnull" is true,
> > otherwise (if "isnull" is false) returns the value of "ret"
> > (true/false).
> > So the following elog needs to be changed (Peter Smith previously
> > pointed this out, but it didn't get completely changed):
> >
> > BEFORE:
> > + elog(DEBUG3, "row filter evaluates to %s (isnull: %s)",
> > + DatumGetBool(ret) ? "true" : "false",
> > + isnull ? "true" : "false");
> > AFTER:
> > + elog(DEBUG3, "row filter evaluates to %s (isnull: %s)",
> > + isnull ? "false" : DatumGetBool(ret) ? "true" : "false",
> > + isnull ? "true" : "false");
> >
>
> Do you see any problem with the current? I find the current one easy
> to understand.
>

Yes, I see a problem. The logging doesn't match what the function code
actually returns when "isnull" is true.
When "isnull" is true, the function always returns false, not the
value of "ret".
For the current logging code to be correct, and match the function
return value, we should be able to change:

  if (isnull)
    return false;

to:

  if (isnull)
    return ret;

But regression tests fail when that code change is made (indicating
that there are cases when "isnull" is true but the function returns
true instead of false).
So the current logging code is NOT correct, and needs to be updated as
I indicated.


Regards,
Greg Nancarrow
Fujitsu Australia