Message-ID: <54CBBB61.1090207@pgmasters.net>
Date: Fri, 30 Jan 2015 12:12:01 -0500
From: David Steele <david@pgmasters.net>
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To: pgsql-hackers@postgresql.org
Subject: Re: tablespaces inside $PGDATA considered harmful
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 <20150130161928.GB20744@momjian.us> <54CBB4AB.1090805@commandprompt.com>
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On 1/30/15 11:43 AM, Joshua D. Drake wrote:
> On 01/30/2015 08:19 AM, Bruce Momjian wrote:
>>
>> On Fri, Jan 30, 2015 at 11:12:43AM -0500, Robert Haas wrote:
>>> I think everyone who has read this mailing list for a while is
>>> probably already aware of this problem.  When you create a tablespace=

>>> somewhere inside the data directory, weird things happen. If you
>>> pg_upgrade and then incautiously run the delete_old_cluster.sh script=

>>> thus created, you will blow away large chunks of your data.[1]  If yo=
u
>>
>> pg_upgrade doesn't create the deletion script in this case, and warns
>> the user:
>>
>>          Could not create a script to delete the old cluster's data
>>          files because user-defined tablespaces exist in the old clust=
er
>>          directory.  The old cluster's contents must be deleted
>> manually.
>>
>>> In the short term, I favor just adding a warning, so that people get
>>> some clue that they are doing something that might be a bad idea.  In=

>>> the long term, we might want to do more.  Thoughts?
>>
>> Yes, good idea.
>
> Uhm, wouldn't it be a rather simple patch to say:
>
> if tablespace_create() in $PGDATA:
>   ERROR!
>
> ?
>
> I mean yes a warning is good but it is after the fact, the tablespace
> is already created. We know that tablespaces in $PGDATA are a bad
> idea, why not protect the user?

I would be in favor of an error.  It would then be OK for basebackup,
pg_upgrade, and friends to error when a tablespace lives in $PGDATA,
rather than trying to deal with the situation in strange ways.

If the user really wants tablespaces in $PGDATA they can always change
the links manually in the filesystem and deal with any consequences on
their own.=20

--=20
- David Steele
david@pgmasters.net


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