Duplicate usage of tablespace location?

Hello,

I noticed by the following report, PostgreSQL can share the same
directory as tablespaces of two servers with different
pg-versions.

https://www.postgresql.org/message-id/2008148.rxBNyNRHPZ@peanuts2

8.4 checked that the tablespace location is empty, but from 9.0,
the check is replaced with creating a PG_PGVER_CATVER
subdirectory. This works for multiple servers with the same
version, but don't for servers with different versions.

This is apparently a bug but doesn't cause any other problem
immediately. If we choose not to do this, the documentaion needs
to be edited instead.

https://www.postgresql.org/docs/9.6/static/manage-ag-tablespaces.html

| The location must be an existing, empty directory that is owned
| by the PostgreSQL operating system user.

regards,

-
Kyotaro Horiguchi
NTT Open Source Software Center