On Tue, 2008-06-03 at 16:48 -0500, Decibel! wrote:
> On May 30, 2008, at 9:51 AM, Simon Riggs wrote:
> > On Thu, 2008-05-29 at 19:18 -0500, Decibel! wrote:
> >> Is there a reason that we can't add a trigger to a table while a
> >> select is running? This is a serious pain when trying to setup
> >> londiste or slony.
> >
> > This is constrained by locking.
> >
> > There are a subset of DDL commands that might be able to be performed
> > with just an ExclusiveLock or ShareLock rather than an
> > Acces***clusiveLock. Nobody has studied which sub-statements this
> > might
> > apply to, but its do-able since CREATE INDEX already does this.
>
> Is there a good way to determine this other than depending on
> knowledge of the source code?
The source doesn't know yet. So just analysis and thinking.
The mechanism to hold less than an Acces***clusiveLock it doesn't exist
yet, but it never will unless we have a list of the things that might be
performed correctly with a lower level of lock.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Sup****t
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