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Re: Question about ALTER TABLE SET TABLESPACE locing

From: Hannu Krosing <hannu(at)skype(dot)net>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Question about ALTER TABLE SET TABLESPACE locing
Date: 2006-02-02 12:26:47
Message-ID: 1138883208.3868.7.camel@localhost.localdomain (view raw or flat)
Thread:
Lists: pgsql-hackers
Ühel kenal päeval, K, 2006-02-01 kell 18:08, kirjutas Tom Lane:
> Hannu Krosing <hannu(at)skype(dot)net> writes:
> > Does ALTER TABLE SET TABLESPACE lock the table
> 
> It had better ... see nearby discussion about relaxing locking for
> TRUNCATE.  

Is it some recent disussion ?

> Exactly the same problem that at commit we'd be cutting
> the ground out from under any concurrent query.

Can't we just keep READ locks and reopen the datafile from its new
location before releasing it ?

Does our shared memory page cache implementation track logical or
physical pages ? If it's just logical pages, then moving the physical
storage around below should not affect it. 

Of course there are problems with WAL/PITR which *have* to deal with
physical storage, but this should be mostly unrelated.

--------------
Hannu



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