Re: tablespaces inside $PGDATA considered harmful

On 01/30/2015 09:19 AM, Stephen Frost wrote:
> * Robert Haas (robertmhaas@gmail.com) wrote:
>> Given all this, it seems like a good idea to at least give a warning
>> if somebody tries to create a tablespace instead the data directory.
> 
> A warning seems like a good idea.  I actually thought we *did* prevent
> it..
> 
>> Arguably, we should prohibit it altogether, but there are obviously
>> people that want to do it, and there could even be somewhat valid
>> reasons for that, like wanting to set per-tablespace settings
>> differently for different tablespaces.  Possibly we should prohibit it
>> anyway, or maybe there should be an option to create a tablespace
>> whose directory is a real directory, not a symlink.  So then:
>>
>> CREATE TABLESPACE foo LOCATION '/home/rhaas/pgdata/pg_tblspc/foo';
>>
>> ...would fail, but if you really want a separate tablespace inside the
>> data directory, we could allow:
>>
>> CREATE TABLESPACE foo NO LOCATION;
>>
>> ...which would just create a bare directory where the symlink would normally go.
> 
> I actually really like this 'NO LOCATION' idea.  Are there reasons why
> that would be difficult or ill-advised to do?
> 
> I could see the NO LOCATION approach being useful for migrating between
> systems, in particular, or a way to have pg_basebackup work that doesn't
> involve having to actually map all the tablespaces...

I like this idea too.  And it would make tablespaces more manageable for
people who are using them for reasons other than putting them on
different disks.

-- 
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com