Re: Bug with pg_basebackup and 'shared' tablespace

At Thu, 06 Apr 2017 00:59:49 +0200, Pierre Ducroquet <p(dot)psql(at)pinaraf(dot)info> wrote in <2008148(dot)rxBNyNRHPZ(at)peanuts2>
> But it all gets messy when we want to create a streaming standby server using
> pg_basebackup. When backuping Pg 9.5, there is no issue, but backuping Pg 9.6
> afterwards will say "directory "/mnt/ssd/postgres" exists but is not empty".

The documentation says as follows.

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.

This explicitly prohibits to share one tablespace directory among
multiple servers. The code is just missing the case of multiple
servers with different versions. I think the bug is rather that
Pg9.6 in the case allowed to create the tablespace.

The current naming rule of tablespace directory was introduced as
of 9.0 so that pg_upgrade (or pg_migrator at the time) can
perform in-place migration. It is not intended to share a
directory among multiple instances with different versions.

That being said, an additional trick in the attached file will
work for you.

regards,

--
Kyotaro Horiguchi
NTT Open Source Software Center