Re: SPI refactoring

pá 8. 11. 2019 v 0:39 odesílatel Mark Dilger <hornschnorter(at)gmail(dot)com>
napsal:

> Hackers,
>
> As discussed with Tom in [1] and again with Pavel and Alvaro in [2],
> here is a partial WIP refactoring of the SPI interface. The goal is to
> remove as many of the SPI_ERROR_xxx codes as possible from the
> interface, replacing them with elog(ERROR), without removing the ability
> of callers to check meaningful return codes and make their own decisions
> about what to do next. The crucial point here is that many of the error
> codes in SPI are "can't happen" or "you made a programmatic mistake"
> type errors that don't require run time remediation, but rather require
> fixing the C code and recompiling. Those seem better handled as an
> elog(ERROR) to avoid the need for tests against such error codes
> sprinkled throughout the system.
>
> One upshot of the refactoring is that some of the SPI functions that
> previously returned an error code can be changed to return void. Tom
> suggested a nice way to use macros to provide backward compatibility
> with older third-party software, and I used his suggestion.
>
> I need guidance with SPI_ERROR_ARGUMENT because it is used by functions
> that don't return an integer error code, but rather return a SPIPlanPtr,
> such as SPI_prepare. Those functions return NULL and set a global
> variable named SPI_result to the error code. I'd be happy to just
> convert this to throwing an error, too, but it is a greater API break
> than anything implemented in the attached patches so far. How do others
> feel about it?
>
> If more places like this can be converted to use elog(ERROR), it may be
> possible to convert more functions to return void.
>
>
> [1] https://www.postgresql.org/message-id/13404.1558558354%40sss.pgh.pa.us
>
> [2]
>
> https://www.postgresql.org/message-id/20191106151112.GA12251%40alvherre.pgsql

Generally lot of API used by extensions are changing - SPI is not
different, and I don't see too much benefit of compatibility API. When you
need to define BACKWARDS_COMPATIBLE_SPI_CALLS, then you can clean code.

It looks for me needlessly. If we change internal API, then should be clean
signal so code should be fixed, so I don't like

-#define SPI_ERROR_PARAM (-7)
+#define SPI_ERROR_PARAM (-7) /* not used anymore */

It should be removed.

I am maybe too aggressive - but because any extension should be compiled
for any postgres release, I don't think so we should to hold some internal
obsolete API. BACKWARDS_COMPATIBLE.. is not used else where, and I would
not to introduce this concept here. It can helps in short perspective, but
it can be trap in long perspective.

Regards

Pavel

> --
> Mark Dilger
>