Re: Moving pg_xlog

"Keith Worthington" <keithw@narrowpathinc.com> writes:
> I have been reading about increasing PostgreSQL performance by relocating the
> pg_xlog to a disk other than the one where the database resides.  I have the
> following pg_xlogs on my system.

> /raid02/databases/pg_xlog
> /raid02/rhdb_databases/pg_xlog
> /raid02/databases-8.0.0/pg_xlog
> /var/lib/pgsql/data/pg_xlog

> I have no idea why the forth entry is there.  It is in the PostgreSQL
> installation directory.

It's there because the RPM sets up a database under /var/lib/pgsql/data.

> 1) stop the postmaster
> 2) rm -rf /var/lib/pgsql/data/pg_xlog
> 3) mv /raid02/databases/pg_xlog /var/lib/pgsql/data/pg_xlog
> 4) ln -s /var/lib/pgsql/data/pg_xlog /raid02/databases/pg_xlog
> 5) start postmaster

Put the xlog anywhere BUT there!!!!!!!!!

> If I can do that and place the pg_xlog in the installation directory will I
> create any installation issues the next time I upgrade PostgreSQL?

Oh, the installation will be just fine ... but your database will not
be after the upgrade wipes out your WAL.  Put the xlog under some
non-system-defined directory.

            regards, tom lane