Re: Weirdness using Executor Hooks

On Thu, Jun 18, 2015 at 5:30 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> If that's broken, then so are most of our contrib modules.
> Certainly none of them have an extra check as suggested by Andres.

I'm putting it in anyways, along with a guard in the actual hook
function to ERROR if prev_hook == my_hook.  At least that'll avoid the
endless loops until I can figure this out.

>
>> 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.

According to the docs, anything listed in 'local_preload_libraries'
has to be in $libdir/plugins (whereas extensions just go to $libdir),
so rather than duplicate the .so, the "copy" in $libdir/plugins is
just a symlink to ../my_extension.so.

Could that be confusing things?

eric