Re: pg_upgrade code questions

Bruce Momjian <bruce(at)momjian(dot)us> writes:
> Takahiro Itagaki wrote:
>> ==== 2. extern PGDLLIMPORT ====
>> pg_upgrade has own definitions of
>> extern PGDLLIMPORT Oid binary_upgrade_next_xxx
>> in pg_upgrade_sysoids.c. But those variables are not declared as
>> PGDLLIMPORT in the core. Can we access unexported variables here?

> The issue here is that you use PGDLLIMPORT where you are importing the
> variable, not where it is defined. For example, look at
> 'seq_page_cost'. You can see PGDLLIMPORT used where it is imported with
> 'extern', but not where is it defined.

Right. Also we are intentionally not exposing those variables in any
backend .h file, because they are not meant for general use. So the
"extern PGDLLIMPORT" isn't going to be in the main backend and has to
be in pg_upgrade. This was discussed awhile ago when we put in those
variables, I believe.

regards, tom lane