Re: Calling PrepareTempTablespaces in BufFileCreateTemp

On Fri, Apr 26, 2019 at 8:05 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> The version that I posted left it to GetNextTempTableSpace to assert
> that. That seemed cleaner to me than an Assert that has to depend
> on interXact.
>
> Running `make check` with [1] applied and one of the calls to
PrepareTempTablespaces commented out, I felt like I deserved more as a
developer than the assertion in this case.

Assertions are especially good to protect against regressions, but, in this
case, I'm just trying to use an API that is being provided.

Assertions don't give me a nice, easy-to-understand test failure. I see that
there was a crash halfway through make check and now I have to figure out
why.

If that is the default way for developers to find out that they are missing
something when using the API, it would be nice if it gave me some sort of
understandable diff or error message.

I also think that if there is a step that a caller should always take before
calling a function, then there needs to be a very compelling reason not to
move
that step into the function itself.

So, just to make sure I understand this case:

PrepareTempTablespaces should not be called in BufFileCreateTemp because it
is
not concerned with temp tablespaces.

OpenTemporaryFile is concerned with temp tablespaces, so any reference to
those
should be there.

However, PrepareTempTablespaces should not be called in OpenTemporaryFile
because it is in fd.c and no functions that make up part of the file
descriptor
API should do catalog lookups.
Is this correct?

[1] https://www.postgresql.org/message-id/11777.1556133426%40sss.pgh.pa.us

--
Melanie Plageman