Thread: on_error table, saving error info to a table

Hi.
I previously did some work in COPY FROM save error information to a table.
still based on this suggestion:
https://www.postgresql.org/message-id/752672.1699474336%40sss.pgh.pa.us
Now I refactored it.

the syntax:
ON_ERROR 'table', TABLE 'error_saving_tbl'

if ON_ERROR is not specified with 'table', TABLE is specified, then error.
if ON_ERROR is specified with 'table', TABLE is not specified or
error_saving_tbl does not exist, then error.

In BeginCopyFrom, we check the data definition of error_saving_table,
we also check if the user has INSERT privilege to error_saving_table
(all the columns).
We also did a preliminary check of the lock condition of error_saving_table.

if it does not meet these conditions, we quickly error out.
error_saving_table will be the same schema as the copy from table.

Because "table" is a keyword, I have to add the following changes to gram.y.
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -3420,6 +3420,10 @@ copy_opt_item:
  {
  $$ = makeDefElem("null", (Node *) makeString($3), @1);
  }
+ | TABLE opt_as Sconst
+ {
+ $$ = makeDefElem("table", (Node *) makeString($3), @1);
+ }

since "table" is already a keyword, so there is no influence on the
parsing speed?

demo:

create table err_tbl(
    userid oid, -- the user oid while copy generated this entry
    copy_tbl oid, --copy table
    filename text,
    lineno  int8,
    line    text,
    colname text,
    raw_field_value text,
    err_message text,
    err_detail text,
    errorcode text
);
create table t_copy_tbl(a int, b int, c int);
COPY t_copy_tbl FROM STDIN WITH (delimiter ',', on_error 'table',
table err_tbl);
1,2,a
\.

table err_tbl \gx
-[ RECORD 1 ]---+-------------------------------------------
userid          | 10
copy_tbl        | 17920
filename        | STDIN
lineno          | 1
line            | 1,2,a
colname         | c
raw_field_value | a
err_message     | invalid input syntax for type integer: "a"
err_detail      |
errorcode       | 22P02

On Mon, Jul 15, 2024 at 1:42 PM Nishant Sharma
<nishant.sharma@enterprisedb.com> wrote:
>
> Thanks for the patch!
>
> I was not able to understand why we need a special error table for COPY?
> Can't we just log it in a new log error file for COPY in a proper format? Like
> using table approach, PG would be unnecessarily be utilising its resources like
> extra CPU to format the data in pages to store in its table format, writing and
> keeping the table in its store (which may or may not be required), the user
> would be required to make sure it creates the error table with proper columns
> to be used in COPY, etc..
>
>
> Meanwhile, please find some quick review comments:-
>
> 1) Patch needs re-base.
>
> 2) If the columns of the error table are fixed, then why not create it internally using
> some function or something instead of making the user create the table correctly
> with all the columns?

I'll think about it more.
previously, i tried to use SPI to create tables, but at that time, i
thought that's kind of excessive.
you need to create the table, check whether the table name is unique,
check the privilege.
now we quickly error out if the error saving table definition does not
meet. I guess that's less work to do.


> 3) I think, error messages can be improved, which looks big to me.
>
> 4) I think no need of below pstrdup, As CStringGetTextDatum creates a text copy for
> the same:-
> err_code = pstrdup(unpack_sql_state(cstate->escontext->error_data->sqlerrcode));
>
> t_values[9] = CStringGetTextDatum(err_code);
>
> 5) Should 'on_error_rel' as not NULL be checked along with below, as I can see it is
> passed as NULL from two locations?
> +               if (cstate->opts.on_error == COPY_ON_ERROR_TABLE)
> +               {
>
> 6) Below declarations can be shifted to the if block, where they are used. Instead of
> keeping them as global in function?
> +   HeapTuple   on_error_tup;
> +   TupleDesc   on_error_tupDesc;
>
> +               if (cstate->opts.on_error == COPY_ON_ERROR_TABLE)
> +               {
>
> 7) Below comment going beyond 80 char width:-
> * if on_error is specified with 'table', then on_error_rel is the error saving table
>
> 8) Need space after 'false'
> err_detail ? false: true;
>
> 9) Below call can fit in a single line. No need to keep the 2nd and 3rd parameter in
> nextlines.
> +                   on_error_tup = heap_form_tuple(on_error_tupDesc,
> +                                                   t_values,
> +                                                   t_isnull);
>
> 10) Variable declarations Tab Spacing issue at multiple places.
>
> 11) Comments in the patch are not matched to PG comment style.
>
>
> Kindly note I have not tested the patch properly yet. Only checked it with a positive test
> case. As I will wait for a conclusion on my opinion of the proposed patch.
>
almost all these issues have been addressed.
The error messages are still not so good. I need to polish it.