Re: Calling PrepareTempTablespaces in BufFileCreateTemp

On Wed, Apr 24, 2019 at 12:17 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> After a bit more thought it seemed like another answer would be to
> make all three of those functions assert that the caller did the
> right thing, as per attached. This addresses the layering-violation
> complaint, but might be more of a pain in the rear for developers.

In what sense is it not already a layering violation to call
PrepareTempTablespaces() as often as we do? PrepareTempTablespaces()
parses and validates the GUC variable and passes it to fd.c, but to me
that seems almost the same as calling the fd.c function
SetTempTablespaces() directly. PrepareTempTablespaces() allocates
memory that it won't free itself within TopTransactionContext. I'm not
seeing why the context that the PrepareTempTablespaces() catalog
access occurs in actually matters.

Like you, I find it hard to prefer one of the approaches over the
other, though I don't really know how to assess this layering
business. I'm glad that either approach will prevent oversights,
though.
--
Peter Geoghegan