Re: Final Thoughts for 8.3 on LWLocking and Scalability

On Tue, 2007-09-11 at 10:21 -0400, Tom Lane wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
> > 1. The ProcArrayLock is acquired Exclusive-ly by only one remaining
> > operation: XidCacheRemoveRunningXids(). Reducing things to that level is
> > brilliant work, Florian and Tom.
> 
> It would be brilliant if it were true, but it isn't.  Better look again.

On the more detailed explanation, I say "in normal operation".

My analytical notes attached to the original post show ProcArrayLock is
acquired exclusively during backend start, exit and while making a
prepared (twophase) commit. So yes, it is locked Exclusively in other
places, but they happen rarely and they actually add/remove procs from
the array, so its unlikely anything can change there anyhow.

--  Simon Riggs 2ndQuadrant  http://www.2ndQuadrant.com