Re: on_error table, saving error info to a table

Hi,

I tested the v10 patch series further on current PostgreSQL HEAD.

The patches applied successfully on my side, and the build/install
completed without issues. I initialized a fresh cluster and verified
that the built-in composite type copy_error_saving is created
correctly during initdb.
I re-tested the COPY functionality using malformed input data and
confirmed that valid rows continue loading successfully while invalid
rows are redirected into ERROR_TABLE with detailed metadata.
I also tried a few additional edge cases.
The self-reference protection works correctly. The following case
correctly errors out:

COPY err_tbl
FROM STDIN
WITH (
ON_ERROR table,
ERROR_TABLE err_tbl
);

with:
cannot use relation "err_tbl" for COPY error saving while copying data to it

I additionally tested ERROR_TABLE behavior with a BEFORE INSERT
trigger attached to err_tbl.
>From my testing, COPY still succeeds and malformed rows continue to be
inserted into err_tbl even when triggers are present on the
ERROR_TABLE. The trigger function also appears to execute normally
during error row insertion. For example, using a trigger function with
RAISE NOTICE produced:

NOTICE: trigger fired
for each malformed row redirected into err_tbl.
Since the patch comments mention restrictions around triggers for
ERROR_TABLE, I was not sure whether this current behavior is
intentional or whether the trigger restriction checks are still
incomplete.
Overall, the executor-based integration in v10 feels cleaner and
easier to follow compared to the earlier versions.

Regards,
Solaimurugan