| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Final Thoughts for 8.3 on LWLocking and Scalability |
| Date: | 2007-09-11 14:44:00 |
| Message-ID: | 1189521840.4281.480.camel@ebony.site |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers pgsql-patches |
On Tue, 2007-09-11 at 10:21 -0400, Tom Lane wrote:
> Simon Riggs <simon(at)2ndquadrant(dot)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
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