Re: Weirdness using Executor Hooks

Eric Ridge <eebbrr(at)gmail(dot)com> writes:
> On Thu, Jun 18, 2015 at 4:42 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> How does your _PG_init() actually look like?

> static ExecutorStart_hook_type prev_ExecutorStartHook = NULL;
> static ExecutorEnd_hook_type prev_ExecutorEndHook = NULL;

> void _PG_init(void)
> {
> prev_ExecutorStartHook = ExecutorStart_hook;
> prev_ExecutorEndHook = ExecutorEnd_hook;

> ExecutorStart_hook = my_executor_start_hook;
> ExecutorEnd_hook = my_executor_end_hook;

> RegisterXactCallback(my_xact_callback, NULL);
> }

If that's broken, then so are most of our contrib modules.
Certainly none of them have an extra check as suggested by Andres.

> As a data point, that might be interesting to know, but I'd still be
> scratching my head about how it happened. Postgres doesn't load an
> extension library more than once per backend session, does it?

It's not supposed to, and AFAICS internal_load_library() will treat
either an exact pathname match or an inode-number match as being
"already loaded". I wonder if you might be doing something that
confuses those checks. It does not look like we try terribly hard
to canonicalize library pathnames --- might you have some references
under different relative paths, for instance? The inode number
check would perhaps fail if you'd installed a new library version,
but it's unclear to me why the pathname check would fail.

regards, tom lane