pg_relation_filepath returning NULL after converting a table back to unencrypted.

[jobinau]

Here is the test case

1. Create an encrypted table

   CREATE TABLE test_tde (id SERIAL, t VARCHAR(32), PRIMARY KEY(id)) USING pg_tde;

2. Insert couple of tuples

   INSERT INTO test_tde  (t) VALUES ('foobar'),('barfoo');

3. Check the details of the table

   postgres=# SELECT relname,relfilenode,pg_relation_filepath(relfilenode) FROM pg_class WHERE relname in ('test_enc','test_tde','test_basic');
   relname   | relfilenode | pg_relation_filepath 
   ------------+-------------+----------------------
   test_tde   |       16502 | base/5/16502
   test_enc   |       16488 | base/5/16488
   test_basic |       16495 | base/5/16495

4. Convert the table back to unencrypted

   ALTER TABLE test_tde SET ACCESS METHOD heap;

5. Check the table status again

   postgres=# SELECT relname,relfilenode,pg_relation_filepath(relfilenode) FROM pg_class WHERE relname in ('test_enc','test_tde','test_basic');
   relname   | relfilenode | pg_relation_filepath 
   ------------+-------------+----------------------
   test_tde   |       16508 | 
   test_enc   |       16488 | base/5/16488
   test_basic |       16495 | base/5/16495
   (3 rows)

   Observe the NULL string returned by the pg_relation_filepath

[ImTheKai]

Will be tracked here https://perconadev.atlassian.net/browse/PG-825