BUG #14522: plpythonu, missed filenode

The following bug has been logged on the website:

Bug reference: 14522
Logged by: Matteo Pasquini
Email address: pasquini(dot)matteo(at)gmail(dot)com
PostgreSQL version: 9.6.1
Operating system: linux x64, debian8
Description:

got: [...] "base/23417/2659":no such file or directory
sqlcode : 58P01
while using plpython functions, usually after 2nd call of a plpython
function.

I've this big python app that cannot be translated entirely in plpython, so
i've managed to
- give to postgres execution of python app (/var/lib/postgresql/pyapp)
- with plpythonu add the path of the app to be able to make import in all
pther functions.

$$
from sys import path
pyapp = '/var/lib/postgresql/pyapp'
if not pyapp in path:
path.append(pyapp)
path = set(path)
$$

- Then, call another plpython function that produce data.
that function convert a file from filesystem and give back a list of values,
it works as expected.

The file "base/23417/2659" is there
-rw------ 1 postgres postgres 80K Feb 1 17:25 base/23417/2659

and both

select * from pg_dabase where oid = 23417;
select * from pg_class where relfilenode = 2659;

returns as expected.

haven't find similar issues around for version 9.6.x

After some tries the error becomes permanent.

Thanks.