Re: SPI: Correct way to rollback a subtransaction?

"Marko Kreen" <markokr@gmail.com> writes:
>     BeginInternalSubTransaction(NULL);
>     res = SPI_connect();
>     if (res < 0)
>         elog(ERROR, "cannot connect to SPI");

>     PG_TRY();
>     {
>         res = SPI_execute("update one row", false, 0);
>         SPI_finish();
>         ReleaseCurrentSubTransaction();
>     }
>     PG_CATCH();
>     {
>         SPI_finish();
>         RollbackAndReleaseCurrentSubTransaction();
>         FlushErrorState();
>         res = -1; /* remember failure */
>     }
>     PG_END_TRY();


This seems like a pretty bad idea: if the SPI_connect fails you lose
control without having unwound the subtransaction.  That's unlikely,
but still wrong.  I think you could do this as
BeginInternalSubTransaction(NULL);PG_TRY();{    res = SPI_connect();    if (res < 0)        elog(ERROR, "cannot connect
toSPI");    res = SPI_execute("update one row", false, 0);    SPI_finish();
ReleaseCurrentSubTransaction();}PG_CATCH();{   /* we expect rollback to clean up inner SPI call */
RollbackAndReleaseCurrentSubTransaction();   FlushErrorState();    res = -1; /* remember failure */}PG_END_TRY();
 

Check the abort-subtrans path but I think it gets you out of the nested
SPI call.  (Because pl_exec.c wants to preserve an already-opened SPI
call, it has to go out of its way to undo this via SPI_restore_connection.
I *think* you don't need that here but am too lazy to check for sure.
Anyway it'll be good practice for you to figure it out for yourself ;-))
        regards, tom lane