Re: Read Uncommitted

On Mon, 2008-05-26 at 20:01 +0900, ITAGAKI Takahiro wrote:
> Simon Riggs <simon@2ndquadrant.com> wrote:
> 
> > The use of this is clear though: allowing long running transactions
> > against unchanging data to not interfere with other activities. It will
> > also have importance in a Hot Standby mode.
> 
> I have an use of the dirty read -- pg_start_backup().
> In 8.3, pg_start_backup takes long time, that is typically
> { checkpoint_timeout * checkpoint_completion_target }.
> 
> If we have some updating transaction during pg_start_backup,
> updated tables cannot be vacuumed well. READ UNCOMMITTED mode
> could help us in such a situation.
> 
>   BEGIN;
>   SET TRANSACTION READ UNCOMMITTED;
>   SELECT pg_start_backup(timeofday());
>   END;
> 

OK, point noted, thanks. Not sure what is possible there yet, but I will
think some more.

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Training, Services and Support