Обсуждение: BUG #19073: there are meaningless code in _SPI_execute_plan() when canSetTag is true

The following bug has been logged on the website:

Bug reference:      19073
Logged by:          Webbo Han
Email address:      webbohan@qq.com
PostgreSQL version: 18.0
Operating system:   all
Description:

In function _SPI_execute_plan(), `my_tuptable` is local variable and
initialized as NULL.
If plan is canSetTag subqueries, `SPI_freetuptable(my_tuptable)` is
meaningless, because `my_tuptable` is NULL.
We'd better remove this code.

On Sat, Oct 4, 2025, at 11:29 PM, PG Bug reporting form wrote:
> In function _SPI_execute_plan(), `my_tuptable` is local variable and
> initialized as NULL.
> If plan is canSetTag subqueries, `SPI_freetuptable(my_tuptable)` is
> meaningless, because `my_tuptable` is NULL.
> We'd better remove this code.
>

There could be multiple statements. The first case will call SPI_freetuptable()
and it is a noop. The code path you are referring to is inside a foreach loop
and a previous statement might set my_tuptable and needs to be freed before
reusing it. That's exactly what the comment says.

            /*
             * The last canSetTag query sets the status values returned to the
             * caller.  Be careful to free any tuptables not returned, to
             * avoid intra-transaction memory leak.
             */
            if (canSetTag)
            {
                my_processed = _SPI_current->processed;
                SPI_freetuptable(my_tuptable);
                my_tuptable = _SPI_current->tuptable;
                my_res = res; 
            }


-- 
Euler Taveira
EDB   https://www.enterprisedb.com/

"Euler Taveira" <euler@eulerto.com> writes:
> On Sat, Oct 4, 2025, at 11:29 PM, PG Bug reporting form wrote:
>> If plan is canSetTag subqueries, `SPI_freetuptable(my_tuptable)` is
>> meaningless, because `my_tuptable` is NULL.

> There could be multiple statements. The first case will call SPI_freetuptable()
> and it is a noop. The code path you are referring to is inside a foreach loop
> and a previous statement might set my_tuptable and needs to be freed before
> reusing it. That's exactly what the comment says.

Yeah.  You'd only reach this case if there were multiple SQL
statements in the string given to SPI_execute() or similar,
but that's perfectly legal.

            regards, tom lane