On Fri, 11 Nov 2005, Josh Berkus wrote:
> Jaime,
>
> > why? seems that REPLACE only work if there are at least one row
> > matching...
>
> Scenario:
>
> session1: REPLACE .... 1
> session2: REPLACE ..... 1
> session1: check to see that "1" exists .... no
> session2: check to see that "1" exists .... no
> session1: INSERT 1
> session2: INSERT 1 .... ERROR
>
> Get the picture? The only way to avoid a race condition is to be able to
> do "predicate locking", that is to lock the table against any data write
> matching that predicate.
When it comes to predicate locking, I think we should defer to Peter's
comment at Open DB Con:
http://www.treehou.se/~swm/peter_merge.jpg
Gavin
