Thread: SQL/PostgreSQL - Error observed in the QUERY not caught by the “EXCEPTION” block in the stored procedure

Eduardo Lúcio Amorim Costa <eduardolucioac@gmail.com> writes:
> my_database=# SELECT file INTO my_file_now FROM public.my_datatable WHERE
> my_id='2fdf5297-8d4a-38bc-bb26-b8a4b7ba47ec';
> ERROR:  missing chunk number 0 for toast value 3483039 in pg_toast_3473493

We've fixed a few bugs over the years that manifest in that type of
problem --- are you up to date on minor releases?  It's also possible
that reindexing that toast table would fix it.

> Based on the above behavior I created the following stored procedure:
> ...
>     my_file_now BYTEA;
> ...
>         SELECT file
>             INTO my_file_now
>             FROM public.my_datatable WHERE my_id=my_id_now;

> QUESTION: Why is the error observed in the query not caught by the
> "EXCEPTION" block in the stored procedure?

I think that plpgsql will not bother to dereference a TOAST pointer
when storing it into a local variable (although this statement is
very possibly version-dependent, and you didn't say what PG version
you are using).

A more reliable way to trigger the problem is to do some computation
that requires the value of the field, perhaps along the lines of

        PERFORM md5(file) FROM public.my_datatable WHERE my_id=my_id_now;


>         EXCEPTION
>             WHEN OTHERS THEN
>             RAISE NOTICE 'CORRUPTED MY_ID - % ', my_id_now;
>             DELETE FROM public.my_datatable WHERE my_id=my_id_now;

I don't know that I'd give a procedure like this license to delete my
entire table :-(.  If you really don't care how much data survives,
why not just TRUNCATE the table and be done with it?  Otherwise,
printing the list of troublesome rows for manual review seems way
more prudent.

                        regards, tom lane

On Sat, Jan 25, 2020 at 5:32 PM Eduardo Lúcio Amorim Costa <eduardolucioac@gmail.com> wrote:

Thanks for the suggestions! I found it a bit strange "pgsql" not to "understand" as an exception the "ERROR:  missing chunk number 0 for toast value 3483039 in pg_toast_3473493"

Please inline or bottom-post here.

I think Tom's point is that the function you wrote never actually attempted to print out the value of the field so the error never got triggered in the function.  You need to actually attempt to manipulate the data to get an error.  If you did get the function to actually encounter the error it should (haven't tested myself) be caught in the exception handler; i.e., "A more reliable way to trigger the problem is to do some computation

that requires the value of the field, perhaps along the lines of [query to try]".

David J.