Re: jsonpath

On 02.03.2018 00:57, Alexander Korotkov wrote:

> On Fri, Mar 2, 2018 at 12:40 AM, Nikita Glukhov
> <n(dot)gluhov(at)postgrespro(dot)ru <mailto:n(dot)gluhov(at)postgrespro(dot)ru>> wrote:
>
> On 28.02.2018 06:55, Robert Haas wrote:
>
> On Mon, Feb 26, 2018 at 10:34 AM, Nikita Glukhov
> <n(dot)gluhov(at)postgrespro(dot)ru <mailto:n(dot)gluhov(at)postgrespro(dot)ru>> wrote:
>
> Attached 10th version of the jsonpath patches.
>
> 1. Fixed error handling in arithmetic operators.
>
>     Now run-time errors in arithmetic operators are
> catched (added
>     PG_TRY/PG_CATCH around operator's functions calls) and
> converted into
>     Unknown values in predicates as it is required by the
> standard:
>
> I think we really need to rename PG_TRY and PG_CATCH or
> rethink this
> whole interface so that people stop thinking they can use it to
> prevent errors from being thrown.
>
>
> I understand that it is unsafe to call arbitrary function inside
> PG_TRY without
> rethrowing of caught errors in PG_CATCH, but in jsonpath only the
> following
> numeric and datetime functions with known behavior are called
> inside PG_TRY
> and only errors of category ERRCODE_DATA_EXCEPTION are caught:
>
> numeric_add()
> numeric_mul()
> numeric_div()
> numeric_mod()
> numeric_float8()
> float8in()
> float8_numeric()
> to_datetime()
>
>
> That seems like a quite limited list of functions. What about
> reworking them
> providing a way of calling them without risk of exception?  For
> example, we can
> have numeric_add_internal() function which fill given data structure with
> error information instead of throwing the error. numeric_add() would be a
> wrapper over numeric_add_internal(), which throws an error if
> corresponding
> data structure is filled.  In jsonpath we can call
> numeric_add_internal() and
> interpret errors in another way.  That seems to be better than use of
> PG_TRY
> and PG_CATCH.

Attached 12th version of jsonpath patches.

I added the 7th patch where the following functions were extracted for
safe error handling in jsonpath:

numeric_add_internal()
numeric_sub_internal()
numeric_mul_internal()
numeric_div_internal()
numeric_mod_internal()
float8_numeric_internal()
numeric_float8_internal()
float8in_internal()

Errors are passed to caller with new ereport_safe() macro when
ErrorData **edata is not NULL:

+#define ereport_safe(edata, elevel, rest) \
+ do { \
+ if (edata) { \
+ errstart(elevel, __FILE__, __LINE__, PG_FUNCNAME_MACRO, TEXTDOMAIN); \
+ (rest); \
+ *(edata) = CopyErrorData(); \
+ FlushErrorState(); \
+ } else { \
+ ereport(elevel, rest); \
+ } \
+ } while (0)

But to_datetime() is still called in jsonpath inside PG_TRY/PG_CATCH block
because it needs too deep error propagation.

--
Nikita Glukhov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company