On Tue, Dec 26, 2006 at 12:04:40PM -0500, D'Arcy J.M. Cain wrote:
> I have been testing this statement and find that it seems not quite
> true. Although ctid changes on update, VACUUM FULL does not change it.
> What it does do is make lower areas available again so an update after a
> VACUUM FULL can reuse lower numbers rather than higher ones before.
A VACUUM FULL will try to compact a table. Thus if there's a lot of
free space at the beginning, it will move tuples near the end to the
beginning.
> Now it certainly seems to me that it should behave as described given
> the definition of VACUUM FULL so I am a little confused by my tests.
> My test table only has two entries in it. Is that the issue? In fact,
> I find the same behaviour if I do a simple VACUUM on the table.
On a table with two entries, VACUUM FULL is going to do nothing of
interest. Moving tuples within a page is useless, generally.
Have a nice day,
--
Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.