Alvaro Herrera wrote:
> On Wed, Mar 23, 2005 at 10:42:01AM +0800, Christopher Kings-Lynne wrote:
> > >>If you want to be my friend forever, then fix CLUSTER so that it uses
> > >>sharerowexclusive as well :D
> > >
> > >I don't think it's as easy as that, because you have to move tuples
> > >around in the cluster operation. Same sort of issue as vacuum full I
> > >would suggest.
> >
> > Cluster doesn't move rows...
> >
> > I didn't say it was easy. It would involve changing how cluster works.
> > It would keep the old table around while building the new, then grab
> > an exclusive lock to swap the two.
>
> Huh, cluster already does that.
>
> I don't remember what the rationale was for locking the table, leaving
> even simple SELECTs out. (In fact, IIRC the decision wasn't made by me,
> and it wasn't discussed at all.)
>
The issue is that we would have to escalate the shared lock to exclusive
to swap out the files, and lock escallation could lead to
deadlock/starvation.
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