Robert, Stephen, etc.:
Apparently you can create a tablespace in the tablespace directory:
josh=# create tablespace tbl location '/home/josh/pg94/data/pg_tblspc/';
CREATE TABLESPACE
josh=# create table test_tbl ( test text ) tablespace tbl;
CREATE TABLE
josh=# \q
josh@Radegast:~/pg94/data/pg_tblspc$ ls
17656 PG_9.4_201409291
josh@Radegast:~/pg94/data/pg_tblspc$ ls -l
total 4
lrwxrwxrwx 1 josh josh 30 Jan 30 13:02 17656 ->
/home/josh/pg94/data/pg_tblspc
drwx------ 3 josh josh 4096 Jan 30 13:02 PG_9.4_201409291
josh@Radegast:~/pg94/data/pg_tblspc$
In theory if I could guess the next OID, I could cause a failure there,
but that appears to be obscure enough to be not worth bothering about.
What is a real problem is that we don't block creating tablespaces
anywhere at all, including in obviously problematic places like the
transaction log directory:
josh=# create tablespace tbl2 location '/home/josh/pg94/data/pg_xlog/';
CREATE TABLESPACE
It really seems like we ought to block *THAT*. Of course, if we block
tablespace creation in PGDATA generally, then that's covered.
--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com